1
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Toulme E, Murach J, Bärfuss S, Kroll J, Malsam J, Trimbuch T, Herman MA, Söllner TH, Rosenmund C. Mutations of Single Residues in the Complexin N-terminus Exhibit Distinct Phenotypes in Synaptic Vesicle Fusion. J Neurosci 2024; 44:e0076242024. [PMID: 38951039 PMCID: PMC11293444 DOI: 10.1523/jneurosci.0076-24.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2024] [Revised: 04/11/2024] [Accepted: 06/07/2024] [Indexed: 07/03/2024] Open
Abstract
The release of neurotransmitters (NTs) at central synapses is dependent on a cascade of protein interactions, specific to the presynaptic compartment. Among those dedicated molecules, the cytosolic complexins play an incompletely defined role as synaptic transmission regulators. Complexins are multidomain proteins that bind soluble N-ethylmaleimide sensitive factor attachment protein receptor complexes, conferring both inhibitory and stimulatory functions. Using systematic mutagenesis and comparing reconstituted in vitro membrane fusion assays with electrophysiology in cultured neurons from mice of either sex, we deciphered the function of the N-terminus of complexin (Cpx) II. The N-terminus (amino acid 1-27) starts with a region enriched in hydrophobic amino acids (1-12), which binds lipids. Mutants maintaining this hydrophobic character retained the stimulatory function of Cpx, whereas exchanges introducing charged residues perturbed both spontaneous and evoked exocytosis. Mutants in the more distal region of the N-terminal domain (amino acid 11-18) showed a spectrum of effects. On the one hand, mutation of residue A12 increased spontaneous release without affecting evoked release. On the other hand, replacing D15 with amino acids of different shapes or hydrophobic properties (but not charge) not only increased spontaneous release but also impaired evoked release. Most surprising, this substitution reduced the size of the readily releasable pool, a novel function for Cpx at mammalian synapses. Thus, the exact amino acid composition of the Cpx N-terminus fine-tunes the degree of spontaneous and evoked NT release.
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Affiliation(s)
- Estelle Toulme
- Charite - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Neurophysiology, 10117 Berlin, Germany
| | - Jacqueline Murach
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany
| | - Simon Bärfuss
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany
| | - Jana Kroll
- Charite - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Neurophysiology, 10117 Berlin, Germany
| | - Jörg Malsam
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany
| | - Thorsten Trimbuch
- Charite - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Neurophysiology, 10117 Berlin, Germany
| | - Melissa A Herman
- Charite - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Neurophysiology, 10117 Berlin, Germany
| | - Thomas H Söllner
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany
| | - Christian Rosenmund
- Charite - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Neurophysiology, 10117 Berlin, Germany
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2
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Bhaskar BR, Yadav L, Sriram M, Sanghrajka K, Gupta M, V BK, Nellikka RK, Das D. Differential SNARE chaperoning by Munc13-1 and Munc18-1 dictates fusion pore fate at the release site. Nat Commun 2024; 15:4132. [PMID: 38755165 PMCID: PMC11099066 DOI: 10.1038/s41467-024-46965-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Accepted: 03/14/2024] [Indexed: 05/18/2024] Open
Abstract
The regulated release of chemical messengers is crucial for cell-to-cell communication; abnormalities in which impact coordinated human body function. During vesicular secretion, multiple SNARE complexes assemble at the release site, leading to fusion pore opening. How membrane fusion regulators act on heterogeneous SNARE populations to assemble fusion pores in a timely and synchronized manner, is unknown. Here, we demonstrate the role of SNARE chaperones Munc13-1 and Munc18-1 in rescuing individual nascent fusion pores from their diacylglycerol lipid-mediated inhibitory states. At the onset of membrane fusion, Munc13-1 clusters multiple SNARE complexes at the release site and synchronizes release events, while Munc18-1 stoichiometrically interacts with trans-SNARE complexes to enhance N- to C-terminal zippering. When both Munc proteins are present simultaneously, they differentially access dynamic trans-SNARE complexes to regulate pore properties. Overall, Munc proteins' direct action on fusion pore assembly indicates their role in controlling quantal size during vesicular secretion.
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Affiliation(s)
- Bhavya R Bhaskar
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Laxmi Yadav
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Malavika Sriram
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Kinjal Sanghrajka
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Mayank Gupta
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Boby K V
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Rohith K Nellikka
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Debasis Das
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India.
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3
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Xu J, Esser V, Gołębiowska-Mendroch K, Bolembach AA, Rizo J. Control of Munc13-1 Activity by Autoinhibitory Interactions Involving the Variable N-terminal Region. J Mol Biol 2024; 436:168502. [PMID: 38417672 PMCID: PMC11384659 DOI: 10.1016/j.jmb.2024.168502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2023] [Revised: 02/17/2024] [Accepted: 02/20/2024] [Indexed: 03/01/2024]
Abstract
Regulation of neurotransmitter release during presynaptic plasticity underlies varied forms of information processing in the brain. Munc13s play essential roles in release via their conserved C-terminal region, which contains a MUN domain involved in SNARE complex assembly, and controls multiple presynaptic plasticity processes. Munc13s also have a variable N-terminal region, which in Munc13-1 includes a calmodulin binding (CaMb) domain involved in short-term plasticity and a C2A domain that forms an inhibitory homodimer. The C2A domain is activated by forming a heterodimer with the zinc-finger domain of αRIMs, providing a link to αRIM-dependent short- and long-term plasticity. However, it is unknown how the functions of the N- and C-terminal regions are integrated, in part because of the difficulty of purifying Munc13-1 fragments containing both regions. We describe for the first time the purification of a Munc13-1 fragment spanning its entire sequence except for a flexible region between the C2A and CaMb domains. We show that this fragment is much less active than the Munc13-1 C-terminal region in liposome fusion assays and that its activity is strongly enhanced by the RIM2α zinc-finger domain together with calmodulin. NMR experiments show that the C2A and CaMb domains bind to the MUN domain and that these interactions are relieved by the RIM2α ZF domain and calmodulin, respectively. These results suggest a model whereby Munc13-1 activity in promoting SNARE complex assembly and neurotransmitter release are inhibited by interactions of the C2A and CaMb domains with the MUN domain that are relieved by αRIMs and calmodulin.
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Affiliation(s)
- Junjie Xu
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Victoria Esser
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Katarzyna Gołębiowska-Mendroch
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Agnieszka A Bolembach
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Josep Rizo
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
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4
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Meijer M, Öttl M, Yang J, Subkhangulova A, Kumar A, Feng Z, van Voorst TW, Groffen AJ, van Weering JRT, Zhang Y, Verhage M. Tomosyns attenuate SNARE assembly and synaptic depression by binding to VAMP2-containing template complexes. Nat Commun 2024; 15:2652. [PMID: 38531902 PMCID: PMC10965968 DOI: 10.1038/s41467-024-46828-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2023] [Accepted: 03/12/2024] [Indexed: 03/28/2024] Open
Abstract
Tomosyns are widely thought to attenuate membrane fusion by competing with synaptobrevin-2/VAMP2 for SNARE-complex assembly. Here, we present evidence against this scenario. In a novel mouse model, tomosyn-1/2 deficiency lowered the fusion barrier and enhanced the probability that synaptic vesicles fuse, resulting in stronger synapses with faster depression and slower recovery. While wild-type tomosyn-1m rescued these phenotypes, substitution of its SNARE motif with that of synaptobrevin-2/VAMP2 did not. Single-molecule force measurements indeed revealed that tomosyn's SNARE motif cannot substitute synaptobrevin-2/VAMP2 to form template complexes with Munc18-1 and syntaxin-1, an essential intermediate for SNARE assembly. Instead, tomosyns extensively bind synaptobrevin-2/VAMP2-containing template complexes and prevent SNAP-25 association. Structure-function analyses indicate that the C-terminal polybasic region contributes to tomosyn's inhibitory function. These results reveal that tomosyns regulate synaptic transmission by cooperating with synaptobrevin-2/VAMP2 to prevent SNAP-25 binding during SNARE assembly, thereby limiting initial synaptic strength and equalizing it during repetitive stimulation.
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Affiliation(s)
- Marieke Meijer
- Department of Human Genetics, Center for Neurogenomics and Cognitive Research, Amsterdam University Medical Center, 1081HV, Amsterdam, The Netherlands.
| | - Miriam Öttl
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Vrije Universiteit Amsterdam, 1081HV, Amsterdam, The Netherlands
| | - Jie Yang
- Department of Cell Biology, Yale School of Medicine, New Haven, CT, 06511, USA.
| | - Aygul Subkhangulova
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Vrije Universiteit Amsterdam, 1081HV, Amsterdam, The Netherlands
| | - Avinash Kumar
- Department of Cell Biology, Yale School of Medicine, New Haven, CT, 06511, USA
| | - Zicheng Feng
- Department of Cell Biology, Yale School of Medicine, New Haven, CT, 06511, USA
| | - Torben W van Voorst
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Vrije Universiteit Amsterdam, 1081HV, Amsterdam, The Netherlands
| | - Alexander J Groffen
- Department of Human Genetics, Center for Neurogenomics and Cognitive Research, Amsterdam University Medical Center, 1081HV, Amsterdam, The Netherlands
| | - Jan R T van Weering
- Department of Human Genetics, Center for Neurogenomics and Cognitive Research, Amsterdam University Medical Center, 1081HV, Amsterdam, The Netherlands
| | - Yongli Zhang
- Department of Cell Biology, Yale School of Medicine, New Haven, CT, 06511, USA.
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06511, USA.
| | - Matthijs Verhage
- Department of Human Genetics, Center for Neurogenomics and Cognitive Research, Amsterdam University Medical Center, 1081HV, Amsterdam, The Netherlands.
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Vrije Universiteit Amsterdam, 1081HV, Amsterdam, The Netherlands.
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5
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Salazar Lázaro A, Trimbuch T, Vardar G, Rosenmund C. The stability of the primed pool of synaptic vesicles and the clamping of spontaneous neurotransmitter release rely on the integrity of the C-terminal half of the SNARE domain of syntaxin-1A. eLife 2024; 12:RP90775. [PMID: 38512129 PMCID: PMC10957171 DOI: 10.7554/elife.90775] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/22/2024] Open
Abstract
The SNARE proteins are central in membrane fusion and, at the synapse, neurotransmitter release. However, their involvement in the dual regulation of the synchronous release while maintaining a pool of readily releasable vesicles remains unclear. Using a chimeric approach, we performed a systematic analysis of the SNARE domain of STX1A by exchanging the whole SNARE domain or its N- or C-terminus subdomains with those of STX2. We expressed these chimeric constructs in STX1-null hippocampal mouse neurons. Exchanging the C-terminal half of STX1's SNARE domain with that of STX2 resulted in a reduced RRP accompanied by an increased release rate, while inserting the C-terminal half of STX1's SNARE domain into STX2 leads to an enhanced priming and decreased release rate. Additionally, we found that the mechanisms for clamping spontaneous, but not for Ca2+-evoked release, are particularly susceptible to changes in specific residues on the outer surface of the C-terminus of the SNARE domain of STX1A. Particularly, mutations of D231 and R232 affected the fusogenicity of the vesicles. We propose that the C-terminal half of the SNARE domain of STX1A plays a crucial role in the stabilization of the RRP as well as in the clamping of spontaneous synaptic vesicle fusion through the regulation of the energetic landscape for fusion, while it also plays a covert role in the speed and efficacy of Ca2+-evoked release.
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Affiliation(s)
- Andrea Salazar Lázaro
- Department of Neurophysiology, Charité-Universitätsmedizin Berlin, Humboldt-Universität zu Berlin, Berlin Institute of HealthBerlinGermany
| | - Thorsten Trimbuch
- Department of Neurophysiology, Charité-Universitätsmedizin Berlin, Humboldt-Universität zu Berlin, Berlin Institute of HealthBerlinGermany
| | - Gülçin Vardar
- Department of Neurophysiology, Charité-Universitätsmedizin Berlin, Humboldt-Universität zu Berlin, Berlin Institute of HealthBerlinGermany
| | - Christian Rosenmund
- Department of Neurophysiology, Charité-Universitätsmedizin Berlin, Humboldt-Universität zu Berlin, Berlin Institute of HealthBerlinGermany
- NeuroCure Excellence ClusterBerlinGermany
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6
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Kádková A, Murach J, Østergaard M, Malsam A, Malsam J, Lolicato F, Nickel W, Söllner TH, Sørensen JB. SNAP25 disease mutations change the energy landscape for synaptic exocytosis due to aberrant SNARE interactions. eLife 2024; 12:RP88619. [PMID: 38411501 PMCID: PMC10911398 DOI: 10.7554/elife.88619] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/28/2024] Open
Abstract
SNAP25 is one of three neuronal SNAREs driving synaptic vesicle exocytosis. We studied three mutations in SNAP25 that cause epileptic encephalopathy: V48F, and D166Y in the synaptotagmin-1 (Syt1)-binding interface, and I67N, which destabilizes the SNARE complex. All three mutations reduced Syt1-dependent vesicle docking to SNARE-carrying liposomes and Ca2+-stimulated membrane fusion in vitro and when expressed in mouse hippocampal neurons. The V48F and D166Y mutants (with potency D166Y > V48F) led to reduced readily releasable pool (RRP) size, due to increased spontaneous (miniature Excitatory Postsynaptic Current, mEPSC) release and decreased priming rates. These mutations lowered the energy barrier for fusion and increased the release probability, which are gain-of-function features not found in Syt1 knockout (KO) neurons; normalized mEPSC release rates were higher (potency D166Y > V48F) than in the Syt1 KO. These mutations (potency D166Y > V48F) increased spontaneous association to partner SNAREs, resulting in unregulated membrane fusion. In contrast, the I67N mutant decreased mEPSC frequency and evoked EPSC amplitudes due to an increase in the height of the energy barrier for fusion, whereas the RRP size was unaffected. This could be partly compensated by positive charges lowering the energy barrier. Overall, pathogenic mutations in SNAP25 cause complex changes in the energy landscape for priming and fusion.
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Affiliation(s)
- Anna Kádková
- Department of Neuroscience, University of CopenhagenCopenhagenDenmark
| | | | - Maiken Østergaard
- Department of Neuroscience, University of CopenhagenCopenhagenDenmark
| | - Andrea Malsam
- Heidelberg University Biochemistry CenterHeidelbergDenmark
| | - Jörg Malsam
- Heidelberg University Biochemistry CenterHeidelbergDenmark
| | - Fabio Lolicato
- Heidelberg University Biochemistry CenterHeidelbergDenmark
- Department of Physics, University of HelsinkiHelsinkiFinland
| | - Walter Nickel
- Heidelberg University Biochemistry CenterHeidelbergDenmark
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7
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Xu J, Esser V, Gołębiowska-Mendroch K, Bolembach AA, Rizo J. Control of Munc13-1 Activity by Autoinhibitory Interactions Involving the Variable N-terminal Region. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.24.577102. [PMID: 38328168 PMCID: PMC10849727 DOI: 10.1101/2024.01.24.577102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2024]
Abstract
Regulation of neurotransmitter release during presynaptic plasticity underlies varied forms of information processing in the brain. Munc13s play essential roles in release via their conserved C-terminal region, which contains a MUN domain involved SNARE complex assembly, and control multiple presynaptic plasticity processes. Munc13s also have a variable N-terminal region, which in Munc13-1 includes a calmodulin binding (CaMb) domain involved in short-term plasticity and a C2A domain that forms an inhibitory homodimer. The C2A domain is activated by forming a heterodimer with the zinc-finger domain of αRIMs, providing a link to αRIM-dependent short- and long-term plasticity. However, it is unknown how the functions of the N- and C-terminal regions are integrated, in part because of the difficulty of purifying Munc13-1 fragments containing both regions. We describe for the first time the purification of a Munc13-1 fragment spanning its entire sequence except for a flexible region between the C2A and CaMb domains. We show that this fragment is much less active than the Munc13-1 C-terminal region in liposome fusion assays and that its activity is strongly enhanced by the RIM2α zinc-finger domain together with calmodulin. NMR experiments show that the C2A and CaMb domains bind to the MUN domain and that these interactions are relieved by the RIM2α ZF domain and calmodulin, respectively. These results suggest a model whereby Munc13-1 activity in promoting SNARE complex assembly and neurotransmitter release are inhibited by interactions of the C2A and CaMb domains with the MUN domain that are relieved by αRIMs and calmodulin.
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Affiliation(s)
- Junjie Xu
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
| | - Victoria Esser
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
| | - Katarzyna Gołębiowska-Mendroch
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Current address: Jagiellonian University, Faculty of Chemistry, Department of Organic Chemistry, Gronostajowa 2, 30-387, Krakow, Poland
| | - Agnieszka A Bolembach
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Current address: Dioscuri Centre for RNA-Protein Interactions in Human Health and Disease, International Institute of Molecular and Cell Biology in Warsaw, 4 Ks. Trojdena Street, 02-109 Warsaw, Poland
| | - Josep Rizo
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
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8
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Toulme E, Murach J, Bärfuss S, Kroll J, Malsam J, Trimbuch T, Herman MA, Söllner TH, Rosenmund C. Single residues in the complexin N-terminus exhibit distinct phenotypes in synaptic vesicle fusion. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.12.575336. [PMID: 38260673 PMCID: PMC10802614 DOI: 10.1101/2024.01.12.575336] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
The release of neurotransmitters at central synapses is dependent on a cascade of protein interactions, specific to the presynaptic compartment. Amongst those dedicated molecules the cytosolic complexins play an incompletely defined role as synaptic transmission regulators. Complexins are multidomain SNARE complex binding proteins which confer both inhibitory and stimulatory functions. Using systematic mutagenesis and combining reconstituted in vitro membrane fusion assays with electrophysiology in neurons, we deciphered the function of the N-terminus of complexin II (Cpx). The N-terminus (amino acid 1 - 27) starts with a region enriched in hydrophobic amino acids (1-12), which can lead to lipid binding. In contrast to mutants which maintain the hydrophobic character and the stimulatory function of Cpx, non-conservative exchanges largely perturbed spontaneous and evoked exocytosis. Mutants in the downstream region (amino acid 11-18) show differential effects. Cpx-A12W increased spontaneous release without affecting evoked release whereas replacing D15 with amino acids of different shapes or hydrophobic properties (but not charge) not only increased spontaneous release, but also impaired evoked release and surprisingly reduced the size of the readily releasable pool, a novel Cpx function, unanticipated from previous studies. Thus, the exact amino acid composition of the Cpx N-terminus fine tunes the degree of spontaneous and evoked neurotransmitter release. Significance Statement We describe in this work the importance of the N-terminal domain of the small regulatory cytosolic protein complexin in spontaneous and evoked glutamatergic neurotransmitter release at hippocampal mouse neurons. We show using a combination of biochemical, imaging and electrophysiological techniques that the binding of the proximal region of complexin (amino acids 1-10) to lipids is crucial for spontaneous synaptic vesicular release. Furthermore, we identify a single amino acid at position D15 which is structurally important since it not only is involved in spontaneous release but, when mutated, also decreases drastically the readily releasable pool, a function that was never attributed to complexin.
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9
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Weichard I, Taschenberger H, Gsell F, Bornschein G, Ritzau-Jost A, Schmidt H, Kittel RJ, Eilers J, Neher E, Hallermann S, Nerlich J. Fully-primed slowly-recovering vesicles mediate presynaptic LTP at neocortical neurons. Proc Natl Acad Sci U S A 2023; 120:e2305460120. [PMID: 37856547 PMCID: PMC10614622 DOI: 10.1073/pnas.2305460120] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Accepted: 08/26/2023] [Indexed: 10/21/2023] Open
Abstract
Pre- and postsynaptic forms of long-term potentiation (LTP) are candidate synaptic mechanisms underlying learning and memory. At layer 5 pyramidal neurons, LTP increases the initial synaptic strength but also short-term depression during high-frequency transmission. This classical form of presynaptic LTP has been referred to as redistribution of synaptic efficacy. However, the underlying mechanisms remain unclear. We therefore performed whole-cell recordings from layer 5 pyramidal neurons in acute cortical slices of rats and analyzed presynaptic function before and after LTP induction by paired pre- and postsynaptic neuronal activity. LTP was successfully induced in about half of the synaptic connections tested and resulted in increased synaptic short-term depression during high-frequency transmission and a decelerated recovery from short-term depression due to an increased fraction of a slow recovery component. Analysis with a recently established sequential two-step vesicle priming model indicates an increase in the abundance of fully-primed and slowly-recovering vesicles. A systematic analysis of short-term plasticity and synapse-to-synapse variability of synaptic strength at various types of synapses revealed that stronger synapses generally recover more slowly from synaptic short-term depression. Finally, pharmacological stimulation of the cyclic adenosine monophosphate and diacylglycerol signaling pathways, which are both known to promote synaptic vesicle priming, mimicked LTP and slowed the recovery from short-term depression. Our data thus demonstrate that LTP at layer 5 pyramidal neurons increases synaptic strength primarily by enlarging a subpool of fully-primed slowly-recovering vesicles.
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Affiliation(s)
- Iron Weichard
- Faculty of Medicine, Carl-Ludwig-Institute for Physiology, Leipzig University, Leipzig04103, Germany
| | - Holger Taschenberger
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen37075, Germany
| | - Felix Gsell
- Faculty of Medicine, Carl-Ludwig-Institute for Physiology, Leipzig University, Leipzig04103, Germany
| | - Grit Bornschein
- Faculty of Medicine, Carl-Ludwig-Institute for Physiology, Leipzig University, Leipzig04103, Germany
| | - Andreas Ritzau-Jost
- Faculty of Medicine, Carl-Ludwig-Institute for Physiology, Leipzig University, Leipzig04103, Germany
| | - Hartmut Schmidt
- Faculty of Medicine, Carl-Ludwig-Institute for Physiology, Leipzig University, Leipzig04103, Germany
| | - Robert J. Kittel
- Department of Animal Physiology, Institute of Biology, Leipzig University, Leipzig04103, Germany
| | - Jens Eilers
- Faculty of Medicine, Carl-Ludwig-Institute for Physiology, Leipzig University, Leipzig04103, Germany
| | - Erwin Neher
- Emeritus Laboratory of Membrane Biophysics, Max Planck Institute for Multidisciplinary Sciences, Göttingen37070, Germany
- Cluster of Excellence “Multiscale Bioimaging: From Molecular Machines to Networks of Excitable Cells”, University of Göttingen, Göttingen37073, Germany
| | - Stefan Hallermann
- Faculty of Medicine, Carl-Ludwig-Institute for Physiology, Leipzig University, Leipzig04103, Germany
| | - Jana Nerlich
- Faculty of Medicine, Carl-Ludwig-Institute for Physiology, Leipzig University, Leipzig04103, Germany
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10
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Das J, You Y, Mathukumalli K, Ann J, Lee J, Marquez VE. Activation of Munc13-1 by Diacylglycerol (DAG)-Lactones. Biochemistry 2023; 62:2717-2726. [PMID: 37651159 DOI: 10.1021/acs.biochem.3c00375] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/01/2023]
Abstract
Munc13-1 is a key protein necessary for vesicle fusion and neurotransmitter release in the brain. Diacylglycerol (DAG)/phorbol ester binds to its C1 domain in the plasma membrane and activates it. The C1 domain of Munc13-1 and protein kinase C (PKC) are homologous in terms of sequence and structure. In order to identify small-molecule modulators of Munc13-1 targeting the C1 domain, we studied the effect of three DAG-lactones, (R,Z)-(2-(hydroxymethyl)-4-(3-isobutyl-5-methylhexylidene)-5-oxotetrahydrofuran-2-yl)methyl pivalate (JH-131e-153), (E)-(2-(hydroxymethyl)-4-(3-isobutyl-5-methylhexylidene)-5-oxotetrahydrofuran-2-yl)methyl pivalate (AJH-836), and (E)-(2-(hydroxymethyl)-4-(4-nitrobenzylidene)-5-oxotetrahydrofuran-2-yl)methyl 4-(dimethylamino)benzoate (130C037), on Munc13-1 activation using the ligand-induced membrane translocation assay. JH-131e-153 showed higher activation than AJH-836, and 130C037 was not able to activate Munc13-1. To understand the role of the ligand-binding site residues in the activation process, three alanine mutants were generated. For AJH-836, the order of activation was wild-type (WT) Munc13-1 > R592A > W588A > I590A. For JH-131e-153, the order of activation was WT > I590 ≈ R592A ≈ W588A. Overall, the Z isomer of DAG-lactones showed higher potency than the E isomer and Trp-588, Ile-590, and Arg-592 were important for its binding. When comparing the activation of Munc13-1 and PKC, the order of activation for JH-131e-153 was PKCα > Munc13-1 > PKCε and for AJH-836, the order of activation was PKCε > PKCα > Munc13-1. Molecular docking supported higher binding of JH-131e-153 than AJH-836 with the Munc13-1 C1 domain. Our results suggest that DAG-lactones have the potential to modulate neuronal processes via Munc13-1 and can be further developed for therapeutic intervention for neurodegenerative diseases.
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Affiliation(s)
- Joydip Das
- Department of Pharmacological & Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, Texas 77204, United States
| | - Youngki You
- Department of Pharmacological & Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, Texas 77204, United States
| | - Kavya Mathukumalli
- Department of Pharmacological & Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, Texas 77204, United States
| | - Jihyae Ann
- College of Pharmacy, Seoul National University, Building 143, Room 507, 1 Gwanak-Ro, Gwanak-Gu, Seoul 08826, Korea
| | - Jeewoo Lee
- College of Pharmacy, Seoul National University, Building 143, Room 507, 1 Gwanak-Ro, Gwanak-Gu, Seoul 08826, Korea
| | - Victor E Marquez
- Center for Cancer Research, Chemical Biology Laboratory, NCI-Frederick, 376 Boyles Street, Frederick, Maryland 21702, United States
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11
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Kalyana Sundaram RV, Chatterjee A, Bera M, Grushin K, Panda A, Li F, Coleman J, Lee S, Ramakrishnan S, Ernst AM, Gupta K, Rothman JE, Krishnakumar SS. Roles for diacylglycerol in synaptic vesicle priming and release revealed by complete reconstitution of core protein machinery. Proc Natl Acad Sci U S A 2023; 120:e2309516120. [PMID: 37590407 PMCID: PMC10450444 DOI: 10.1073/pnas.2309516120] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2023] [Accepted: 07/14/2023] [Indexed: 08/19/2023] Open
Abstract
Here, we introduce the full functional reconstitution of genetically validated core protein machinery (SNAREs, Munc13, Munc18, Synaptotagmin, and Complexin) for synaptic vesicle priming and release in a geometry that enables detailed characterization of the fate of docked vesicles both before and after release is triggered with Ca2+. Using this setup, we identify new roles for diacylglycerol (DAG) in regulating vesicle priming and Ca2+-triggered release involving the SNARE assembly chaperone Munc13. We find that low concentrations of DAG profoundly accelerate the rate of Ca2+-dependent release, and high concentrations reduce clamping and permit extensive spontaneous release. As expected, DAG also increases the number of docked, release-ready vesicles. Dynamic single-molecule imaging of Complexin binding to release-ready vesicles directly establishes that DAG accelerates the rate of SNAREpin assembly mediated by chaperones, Munc13 and Munc18. The selective effects of physiologically validated mutations confirmed that the Munc18-Syntaxin-VAMP2 "template" complex is a functional intermediate in the production of primed, release-ready vesicles, which requires the coordinated action of Munc13 and Munc18.
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Affiliation(s)
- R. Venkat Kalyana Sundaram
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Atrouli Chatterjee
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Manindra Bera
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Kirill Grushin
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Aniruddha Panda
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Feng Li
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Jeff Coleman
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Seong Lee
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Sathish Ramakrishnan
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Pathology, Yale University School of Medicine, New Haven, CT06520
| | - Andreas M. Ernst
- School of Biological Sciences, University of California San Diego, San Diego, CA92093
| | - Kallol Gupta
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - James E. Rothman
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Shyam S. Krishnakumar
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Neurology, Yale University School of Medicine, New Haven, CT06520
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12
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Willemse SW, Harley P, van Eijk RPA, Demaegd KC, Zelina P, Pasterkamp RJ, van Damme P, Ingre C, van Rheenen W, Veldink JH, Kiernan MC, Al-Chalabi A, van den Berg LH, Fratta P, van Es MA. UNC13A in amyotrophic lateral sclerosis: from genetic association to therapeutic target. J Neurol Neurosurg Psychiatry 2023; 94:649-656. [PMID: 36737245 PMCID: PMC10359588 DOI: 10.1136/jnnp-2022-330504] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/05/2022] [Accepted: 01/10/2023] [Indexed: 02/05/2023]
Abstract
Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with limited treatment options and an incompletely understood pathophysiology. Although genomewide association studies (GWAS) have advanced our understanding of the disease, the precise manner in which risk polymorphisms contribute to disease pathogenesis remains unclear. Of relevance, GWAS have shown that a polymorphism (rs12608932) in the UNC13A gene is associated with risk for both ALS and frontotemporal dementia (FTD). Homozygosity for the C-allele at rs12608932 modifies the ALS phenotype, as these patients are more likely to have bulbar-onset disease, cognitive impairment and FTD at baseline as well as shorter survival. UNC13A is expressed in neuronal tissue and is involved in maintaining synaptic active zones, by enabling the priming and docking of synaptic vesicles. In the absence of functional TDP-43, risk variants in UNC13A lead to the inclusion of a cryptic exon in UNC13A messenger RNA, subsequently leading to nonsense mediated decay, with loss of functional protein. Depletion of UNC13A leads to impaired neurotransmission. Recent discoveries have identified UNC13A as a potential target for therapy development in ALS, with a confirmatory trial with lithium carbonate in UNC13A cases now underway and future approaches with antisense oligonucleotides currently under consideration. Considering UNC13A is a potent phenotypic modifier, it may also impact clinical trial outcomes. This present review describes the path from the initial discovery of UNC13A as a risk gene in ALS to the current therapeutic options being explored and how knowledge of its distinct phenotype needs to be taken into account in future trials.
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Affiliation(s)
- Sean W Willemse
- Department of Neurology, UMC Utrecht Brain Center Rudolf Magnus, Utrecht, The Netherlands
| | - Peter Harley
- UCL Queen Square Motor Neuron Disease Centre, Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, London, UK
| | - Ruben P A van Eijk
- Department of Neurology, UMC Utrecht Brain Center Rudolf Magnus, Utrecht, The Netherlands
- Biostatistics & Research Support, Julius Center for Health Sciences and Primary Care, UMC Utrecht, Utrecht, The Netherlands
| | - Koen C Demaegd
- Department of Neurology, UMC Utrecht Brain Center Rudolf Magnus, Utrecht, The Netherlands
| | - Pavol Zelina
- Department of Translational Neuroscience, UMC Utrecht Brain Center Rudolf Magnus, Utrecht, The Netherlands
| | - R Jeroen Pasterkamp
- Department of Translational Neuroscience, UMC Utrecht Brain Center Rudolf Magnus, Utrecht, The Netherlands
| | - Philip van Damme
- Department of Neurology, KU Leuven Hospital, Leuven, Belgium
- Laboratory of Neurobiology, VIB KU Leuven Center for Brain and Disease Research, Leuven, Belgium
| | - Caroline Ingre
- Department of Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden
| | - Wouter van Rheenen
- Department of Neurology, UMC Utrecht Brain Center Rudolf Magnus, Utrecht, The Netherlands
| | - Jan H Veldink
- Department of Neurology, UMC Utrecht Brain Center Rudolf Magnus, Utrecht, The Netherlands
| | - Matthew C Kiernan
- Bushell Chair of Neurology, Brain and Mind Centre, University of Sydney, Sydney, New South Wales, Australia
- Neurology, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia
| | | | - Leonard H van den Berg
- Department of Neurology, UMC Utrecht Brain Center Rudolf Magnus, Utrecht, The Netherlands
| | - Pietro Fratta
- UCL Queen Square Motor Neuron Disease Centre, Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, London, UK
| | - Michael A van Es
- Department of Neurology, UMC Utrecht Brain Center Rudolf Magnus, Utrecht, The Netherlands
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13
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Jusyte M, Blaum N, Böhme MA, Berns MMM, Bonard AE, Vámosi ÁB, Pushpalatha KV, Kobbersmed JRL, Walter AM. Unc13A dynamically stabilizes vesicle priming at synaptic release sites for short-term facilitation and homeostatic potentiation. Cell Rep 2023; 42:112541. [PMID: 37243591 DOI: 10.1016/j.celrep.2023.112541] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Revised: 03/10/2023] [Accepted: 05/03/2023] [Indexed: 05/29/2023] Open
Abstract
Presynaptic plasticity adjusts neurotransmitter (NT) liberation. Short-term facilitation (STF) tunes synapses to millisecond repetitive activation, while presynaptic homeostatic potentiation (PHP) of NT release stabilizes transmission over minutes. Despite different timescales of STF and PHP, our analysis of Drosophila neuromuscular junctions reveals functional overlap and shared molecular dependence on the release-site protein Unc13A. Mutating Unc13A's calmodulin binding domain (CaM-domain) increases baseline transmission while blocking STF and PHP. Mathematical modeling suggests that Ca2+/calmodulin/Unc13A interaction plastically stabilizes vesicle priming at release sites and that CaM-domain mutation causes constitutive stabilization, thereby blocking plasticity. Labeling the functionally essential Unc13A MUN domain reveals higher STED microscopy signals closer to release sites following CaM-domain mutation. Acute phorbol ester treatment similarly enhances NT release and blocks STF/PHP in synapses expressing wild-type Unc13A, while CaM-domain mutation occludes this, indicating common downstream effects. Thus, Unc13A regulatory domains integrate signals across timescales to switch release-site participation for synaptic plasticity.
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Affiliation(s)
- Meida Jusyte
- Molecular and Theoretical Neuroscience, Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany; Einstein Center for Neurosciences Berlin, Charité Universitätsmedizin Berlin, Berlin, Germany
| | - Natalie Blaum
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Mathias A Böhme
- Molecular and Theoretical Neuroscience, Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany; Rudolf Schönheimer Institute of Biochemistry, Division of General Biochemistry, Medical Faculty, Leipzig University, Leipzig, Germany
| | - Manon M M Berns
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Alix E Bonard
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Ábel B Vámosi
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | | | - Janus R L Kobbersmed
- Department of Mathematical Sciences, University of Copenhagen, Copenhagen, Denmark; Center of Functionally Integrative Neuroscience, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Alexander M Walter
- Molecular and Theoretical Neuroscience, Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany; Einstein Center for Neurosciences Berlin, Charité Universitätsmedizin Berlin, Berlin, Germany; Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark.
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14
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Papantoniou C, Laugks U, Betzin J, Capitanio C, Ferrero JJ, Sánchez-Prieto J, Schoch S, Brose N, Baumeister W, Cooper BH, Imig C, Lučić V. Munc13- and SNAP25-dependent molecular bridges play a key role in synaptic vesicle priming. SCIENCE ADVANCES 2023; 9:eadf6222. [PMID: 37343100 DOI: 10.1126/sciadv.adf6222] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2022] [Accepted: 05/17/2023] [Indexed: 06/23/2023]
Abstract
Synaptic vesicle tethering, priming, and neurotransmitter release require a coordinated action of multiple protein complexes. While physiological experiments, interaction data, and structural studies of purified systems were essential for our understanding of the function of the individual complexes involved, they cannot resolve how the actions of individual complexes integrate. We used cryo-electron tomography to simultaneously image multiple presynaptic protein complexes and lipids at molecular resolution in their native composition, conformation, and environment. Our detailed morphological characterization suggests that sequential synaptic vesicle states precede neurotransmitter release, where Munc13-comprising bridges localize vesicles <10 nanometers and soluble N-ethylmaleimide-sensitive factor attachment protein 25-comprising bridges <5 nanometers from the plasma membrane, the latter constituting a molecularly primed state. Munc13 activation supports the transition to the primed state via vesicle bridges to plasma membrane (tethers), while protein kinase C promotes the same transition by reducing vesicle interlinking. These findings exemplify a cellular function performed by an extended assembly comprising multiple molecularly diverse complexes.
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Affiliation(s)
- Christos Papantoniou
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Ulrike Laugks
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Julia Betzin
- Department of Neuropathology, University Hospital of Bonn, 53127 Bonn, Germany
| | - Cristina Capitanio
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - José Javier Ferrero
- Departamento de Bioquímica y Biología Molecular, Facultad de Veterinaria, Universidad Complutense, and Instituto de Investigación Sanitaria del Hospital Clínico San Carlos, 28040 Madrid, Spain
| | - José Sánchez-Prieto
- Departamento de Bioquímica y Biología Molecular, Facultad de Veterinaria, Universidad Complutense, and Instituto de Investigación Sanitaria del Hospital Clínico San Carlos, 28040 Madrid, Spain
| | - Susanne Schoch
- Department of Neuropathology, University Hospital of Bonn, 53127 Bonn, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Multidisciplinary Sciences, City Campus, 37075 Göttingen, Germany
| | - Wolfgang Baumeister
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Benjamin H Cooper
- Department of Molecular Neurobiology, Max Planck Institute of Multidisciplinary Sciences, City Campus, 37075 Göttingen, Germany
| | - Cordelia Imig
- Department of Molecular Neurobiology, Max Planck Institute of Multidisciplinary Sciences, City Campus, 37075 Göttingen, Germany
- Department of Neuroscience, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Vladan Lučić
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
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15
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Sundaram RVK, Chatterjee A, Bera M, Grushin K, Panda A, Li F, Coleman J, Lee S, Ramakrishnan S, Ernst AM, Gupta K, Rothman JE, Krishnakumar SS. Novel Roles for Diacylglycerol in Synaptic Vesicle Priming and Release Revealed by Complete Reconstitution of Core Protein Machinery. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.05.543781. [PMID: 37333317 PMCID: PMC10274626 DOI: 10.1101/2023.06.05.543781] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/20/2023]
Abstract
Here we introduce the full functional reconstitution of genetically-validated core protein machinery (SNAREs, Munc13, Munc18, Synaptotagmin, Complexin) for synaptic vesicle priming and release in a geometry that enables detailed characterization of the fate of docked vesicles both before and after release is triggered with Ca 2+ . Using this novel setup, we discover new roles for diacylglycerol (DAG) in regulating vesicle priming and Ca 2+- triggered release involving the SNARE assembly chaperone Munc13. We find that low concentrations of DAG profoundly accelerate the rate of Ca 2+ -dependent release, and high concentrations reduce clamping and permit extensive spontaneous release. As expected, DAG also increases the number of ready-release vesicles. Dynamic single-molecule imaging of Complexin binding to ready-release vesicles directly establishes that DAG accelerates the rate of SNAREpin assembly mediated by Munc13 and Munc18 chaperones. The selective effects of physiologically validated mutations confirmed that the Munc18-Syntaxin-VAMP2 'template' complex is a functional intermediate in the production of primed, ready-release vesicles, which requires the coordinated action of Munc13 and Munc18. SIGNIFICANCE STATEMENT Munc13 and Munc18 are SNARE-associated chaperones that act as "priming" factors, facilitating the formation of a pool of docked, release-ready vesicles and regulating Ca 2+ -evoked neurotransmitter release. Although important insights into Munc18/Munc13 function have been gained, how they assemble and operate together remains enigmatic. To address this, we developed a novel biochemically-defined fusion assay which enabled us to investigate the cooperative action of Munc13 and Munc18 in molecular terms. We find that Munc18 nucleates the SNARE complex, while Munc13 promotes and accelerates the SNARE assembly in a DAG-dependent manner. The concerted action of Munc13 and Munc18 stages the SNARE assembly process to ensure efficient 'clamping' and formation of stably docked vesicles, which can be triggered to fuse rapidly (∼10 msec) upon Ca 2+ influx.
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Affiliation(s)
- R Venkat Kalyana Sundaram
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Atrouli Chatterjee
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Manindra Bera
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Kirill Grushin
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Aniruddha Panda
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Feng Li
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Jeff Coleman
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Seong Lee
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Sathish Ramakrishnan
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Pathology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Andreas M. Ernst
- School of Biological Sciences, University of California San Diego, La Jolla CA 92093, USA
| | - Kallol Gupta
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - James E. Rothman
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Shyam S. Krishnakumar
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06520, USA
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16
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Mueller BD, Merrill SA, Watanabe S, Liu P, Niu L, Singh A, Maldonado-Catala P, Cherry A, Rich MS, Silva M, Maricq AV, Wang ZW, Jorgensen EM. CaV1 and CaV2 calcium channels mediate the release of distinct pools of synaptic vesicles. eLife 2023; 12:e81407. [PMID: 36820519 PMCID: PMC10023163 DOI: 10.7554/elife.81407] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2022] [Accepted: 02/22/2023] [Indexed: 02/24/2023] Open
Abstract
Activation of voltage-gated calcium channels at presynaptic terminals leads to local increases in calcium and the fusion of synaptic vesicles containing neurotransmitter. Presynaptic output is a function of the density of calcium channels, the dynamic properties of the channel, the distance to docked vesicles, and the release probability at the docking site. We demonstrate that at Caenorhabditis elegans neuromuscular junctions two different classes of voltage-gated calcium channels, CaV2 and CaV1, mediate the release of distinct pools of synaptic vesicles. CaV2 channels are concentrated in densely packed clusters ~250 nm in diameter with the active zone proteins Neurexin, α-Liprin, SYDE, ELKS/CAST, RIM-BP, α-Catulin, and MAGI1. CaV2 channels are colocalized with the priming protein UNC-13L and mediate the fusion of vesicles docked within 33 nm of the dense projection. CaV2 activity is amplified by ryanodine receptor release of calcium from internal stores, triggering fusion up to 165 nm from the dense projection. By contrast, CaV1 channels are dispersed in the synaptic varicosity, and are colocalized with UNC-13S. CaV1 and ryanodine receptors are separated by just 40 nm, and vesicle fusion mediated by CaV1 is completely dependent on the ryanodine receptor. Distinct synaptic vesicle pools, released by different calcium channels, could be used to tune the speed, voltage-dependence, and quantal content of neurotransmitter release.
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Affiliation(s)
- Brian D Mueller
- Howard Hughes Medical Institute, School of Biological Sciences, University of UtahSalt Lake CityUnited States
| | - Sean A Merrill
- Howard Hughes Medical Institute, School of Biological Sciences, University of UtahSalt Lake CityUnited States
| | - Shigeki Watanabe
- Howard Hughes Medical Institute, School of Biological Sciences, University of UtahSalt Lake CityUnited States
| | - Ping Liu
- Department of Neuroscience, University of Connecticut Medical SchoolFarmingtonUnited States
| | - Longgang Niu
- Department of Neuroscience, University of Connecticut Medical SchoolFarmingtonUnited States
| | - Anish Singh
- Howard Hughes Medical Institute, School of Biological Sciences, University of UtahSalt Lake CityUnited States
| | | | - Alex Cherry
- Howard Hughes Medical Institute, School of Biological Sciences, University of UtahSalt Lake CityUnited States
| | - Matthew S Rich
- Howard Hughes Medical Institute, School of Biological Sciences, University of UtahSalt Lake CityUnited States
| | - Malan Silva
- Howard Hughes Medical Institute, School of Biological Sciences, University of UtahSalt Lake CityUnited States
| | | | - Zhao-Wen Wang
- Department of Neuroscience, University of Connecticut Medical SchoolFarmingtonUnited States
| | - Erik M Jorgensen
- Howard Hughes Medical Institute, School of Biological Sciences, University of UtahSalt Lake CityUnited States
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17
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Akefe IO, Osborne SL, Matthews B, Wallis TP, Meunier FA. Lipids and Secretory Vesicle Exocytosis. ADVANCES IN NEUROBIOLOGY 2023; 33:357-397. [PMID: 37615874 DOI: 10.1007/978-3-031-34229-5_14] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Abstract
In recent years, the number of studies implicating lipids in the regulation of synaptic vesicle exocytosis has risen considerably. It has become increasingly clear that lipids such as phosphoinositides, lysophospholipids, cholesterol, arachidonic acid and myristic acid play critical regulatory roles in the processes leading up to exocytosis. Lipids may affect membrane fusion reactions by altering the physical properties of the membrane, recruiting key regulatory proteins, concentrating proteins into exocytic "hotspots" or by modulating protein functions allosterically. Discrete changes in phosphoinositides concentration are involved in multiple trafficking events including exocytosis and endocytosis. Lipid-modifying enzymes such as the DDHD2 isoform of phospholipase A1 were recently shown to contribute to memory acquisition via dynamic modifications of the brain lipid landscape. Considering the increasing reports on neurodegenerative disorders associated with aberrant intracellular trafficking, an improved understanding of the control of lipid pathways is physiologically and clinically significant and will afford unique insights into mechanisms and therapeutic methods for neurodegenerative diseases. Consequently, this chapter will discuss the different classes of lipids, phospholipase enzymes, the evidence linking them to synaptic neurotransmitter release and how they act to regulate key steps in the multi-step process leading to neuronal communication and memory acquisition.
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Affiliation(s)
- Isaac O Akefe
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, Australia
| | - Shona L Osborne
- ARC Training Centre for Innovation in Biomedical Imaging Technology (CIBIT), The University of Queensland, St Lucia, QLD, Australia
| | - Benjamin Matthews
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, Australia
| | - Tristan P Wallis
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, Australia
| | - Frédéric A Meunier
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, Australia.
- School of Biomedical Sciences, The University of Queensland, St Lucia, QLD, Australia.
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18
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Meunier FA, Hu Z. Functional Roles of UNC-13/Munc13 and UNC-18/Munc18 in Neurotransmission. ADVANCES IN NEUROBIOLOGY 2023; 33:203-231. [PMID: 37615868 DOI: 10.1007/978-3-031-34229-5_8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Abstract
Neurotransmitters are released from synaptic and secretory vesicles following calcium-triggered fusion with the plasma membrane. These exocytotic events are driven by assembly of a ternary SNARE complex between the vesicle SNARE synaptobrevin and the plasma membrane-associated SNAREs syntaxin and SNAP-25. Proteins that affect SNARE complex assembly are therefore important regulators of synaptic strength. In this chapter, we review our current understanding of the roles played by two SNARE interacting proteins: UNC-13/Munc13 and UNC-18/Munc18. We discuss results from both invertebrate and vertebrate model systems, highlighting recent advances, focusing on the current consensus on molecular mechanisms of action and nanoscale organization, and pointing out some unresolved aspects of their functions.
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Affiliation(s)
- Frédéric A Meunier
- Clem Jones Centre for Ageing Dementia Research (CJCADR), Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia.
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, Australia.
| | - Zhitao Hu
- Clem Jones Centre for Ageing Dementia Research (CJCADR), Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia.
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19
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Aldahabi M, Balint F, Holderith N, Lorincz A, Reva M, Nusser Z. Different priming states of synaptic vesicles underlie distinct release probabilities at hippocampal excitatory synapses. Neuron 2022; 110:4144-4161.e7. [PMID: 36261033 PMCID: PMC9796815 DOI: 10.1016/j.neuron.2022.09.035] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Revised: 07/28/2022] [Accepted: 09/27/2022] [Indexed: 12/12/2022]
Abstract
A stunning example of synaptic diversity is the postsynaptic target cell-type-dependent difference in synaptic efficacy in cortical networks. Here, we show that CA1 pyramidal cell (PC) to fast spiking interneuron (FSIN) connections have 10-fold larger release probability (Pv) than those on oriens lacunosum-moleculare (O-LM) interneurons. Freeze-fracture immunolabeling revealed that different nano-topologies and coupling distances between Ca2+ channels and release sites (RSs) are not responsible for the distinct Pv. Although [Ca2+] transients are 40% larger in FSINs innervating boutons, when [Ca2+] entry is matched in the two bouton populations, EPSCs in O-LM cells are still 7-fold smaller. However, application of a phorbol ester analog resulted in a ∼2.5-fold larger augmentation at PC - O-LM compared to PC - FSIN synapses, suggesting incomplete docking or priming of vesicles. Similar densities of docked vesicles rule out distinct RS occupancies and demonstrate that incompletely primed, but docked, vesicles limit the output of PC - O-LM synapses.
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Affiliation(s)
- Mohammad Aldahabi
- Laboratory of Cellular Neurophysiology, Institute of Experimental Medicine, Budapest 1083, Hungary,János Szentágothai School of Neurosciences, Semmelweis University, Budapest, Hungary
| | - Flora Balint
- Laboratory of Cellular Neurophysiology, Institute of Experimental Medicine, Budapest 1083, Hungary
| | - Noemi Holderith
- Laboratory of Cellular Neurophysiology, Institute of Experimental Medicine, Budapest 1083, Hungary
| | - Andrea Lorincz
- Laboratory of Cellular Neurophysiology, Institute of Experimental Medicine, Budapest 1083, Hungary
| | - Maria Reva
- Unit of Synapse and Circuit Dynamics, CNRS UMR 3571, Institute Pasteur, Paris, France
| | - Zoltan Nusser
- Laboratory of Cellular Neurophysiology, Institute of Experimental Medicine, Budapest 1083, Hungary,Corresponding author
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20
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Cruz E, Bessières B, Magistretti P, Alberini CM. Differential role of neuronal glucose and PFKFB3 in memory formation during development. Glia 2022; 70:2207-2231. [PMID: 35916383 PMCID: PMC9474594 DOI: 10.1002/glia.24248] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2022] [Revised: 06/21/2022] [Accepted: 07/05/2022] [Indexed: 11/06/2022]
Abstract
The consumption of glucose in the brain peaks during late childhood; yet, whether and how glucose metabolism is differentially regulated in the brain during childhood compared to adulthood remains to be understood. In particular, it remains to be determined how glucose metabolism is involved in behavioral activations such as learning. Here we show that, compared to adult, the juvenile rat hippocampus has significantly higher mRNA levels of several glucose metabolism enzymes belonging to all glucose metabolism pathways, as well as higher levels of the monocarboxylate transporters MCT1 and MCT4 and the glucose transporters endothelial-GLUT1 and GLUT3 proteins. Furthermore, relative to adults, long-term episodic memory formation in juvenile animals requires significantly higher rates of aerobic glycolysis and astrocytic-neuronal lactate coupling in the hippocampus. Only juvenile but not adult long-term memory formation recruits GLUT3, neuronal 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) and more efficiently engages glucose in the hippocampus. Hence, compared to adult, the juvenile hippocampus distinctively regulates glucose metabolism pathways, and formation of long-term memory in juveniles involves differential neuronal glucose metabolism mechanisms.
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Affiliation(s)
- Emmanuel Cruz
- Center for Neural Science, New York University, New York, New York 10003
| | - Benjamin Bessières
- Center for Neural Science, New York University, New York, New York 10003
| | - Pierre Magistretti
- Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia
| | - Cristina M. Alberini
- Center for Neural Science, New York University, New York, New York 10003
- Lead contact: Cristina M. Alberini
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21
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Rizo J, David G, Fealey ME, Jaczynska K. On the difficulties of characterizing weak protein interactions that are critical for neurotransmitter release. FEBS Open Bio 2022; 12:1912-1938. [PMID: 35986639 PMCID: PMC9623538 DOI: 10.1002/2211-5463.13473] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Revised: 08/09/2022] [Accepted: 08/18/2022] [Indexed: 01/25/2023] Open
Abstract
The mechanism of neurotransmitter release has been extensively characterized, showing that vesicle fusion is mediated by the SNARE complex formed by syntaxin-1, SNAP-25 and synaptobrevin. This complex is disassembled by N-ethylmaleimide sensitive factor (NSF) and SNAPs to recycle the SNAREs, whereas Munc18-1 and Munc13s organize SNARE complex assembly in an NSF-SNAP-resistant manner. Synaptotagmin-1 acts as the Ca2+ sensor that triggers exocytosis in a tight interplay with the SNAREs and complexins. Here, we review technical aspects associated with investigation of protein interactions underlying these steps, which is hindered because the release machinery is assembled between two membranes and is highly dynamic. Moreover, weak interactions, which are difficult to characterize, play key roles in neurotransmitter release, for instance by lowering energy barriers that need to be overcome in this highly regulated process. We illustrate the crucial role that structural biology has played in uncovering mechanisms underlying neurotransmitter release, but also discuss the importance of considering the limitations of the techniques used, including lessons learned from research in our lab and others. In particular, we emphasize: (a) the promiscuity of some protein sequences, including membrane-binding regions that can mediate irrelevant interactions with proteins in the absence of their native targets; (b) the need to ensure that weak interactions observed in crystal structures are biologically relevant; and (c) the limitations of isothermal titration calorimetry to analyze weak interactions. Finally, we stress that even studies that required re-interpretation often helped to move the field forward by improving our understanding of the system and providing testable hypotheses.
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Affiliation(s)
- Josep Rizo
- Department of BiophysicsUniversity of Texas Southwestern Medical CenterDallasTXUSA,Department of BiochemistryUniversity of Texas Southwestern Medical CenterDallasTXUSA,Department of PharmacologyUniversity of Texas Southwestern Medical CenterDallasTXUSA
| | - Guillaume David
- Department of BiophysicsUniversity of Texas Southwestern Medical CenterDallasTXUSA,Department of BiochemistryUniversity of Texas Southwestern Medical CenterDallasTXUSA,Department of PharmacologyUniversity of Texas Southwestern Medical CenterDallasTXUSA
| | - Michael E. Fealey
- Department of BiophysicsUniversity of Texas Southwestern Medical CenterDallasTXUSA,Department of BiochemistryUniversity of Texas Southwestern Medical CenterDallasTXUSA,Department of PharmacologyUniversity of Texas Southwestern Medical CenterDallasTXUSA
| | - Klaudia Jaczynska
- Department of BiophysicsUniversity of Texas Southwestern Medical CenterDallasTXUSA,Department of BiochemistryUniversity of Texas Southwestern Medical CenterDallasTXUSA,Department of PharmacologyUniversity of Texas Southwestern Medical CenterDallasTXUSA
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22
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Knodel MM, Dutta Roy R, Wittum G. Influence of T-Bar on Calcium Concentration Impacting Release Probability. Front Comput Neurosci 2022; 16:855746. [PMID: 35586479 PMCID: PMC9108211 DOI: 10.3389/fncom.2022.855746] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2022] [Accepted: 03/09/2022] [Indexed: 11/25/2022] Open
Abstract
The relation of form and function, namely the impact of the synaptic anatomy on calcium dynamics in the presynaptic bouton, is a major challenge of present (computational) neuroscience at a cellular level. The Drosophila larval neuromuscular junction (NMJ) is a simple model system, which allows studying basic effects in a rather simple way. This synapse harbors several special structures. In particular, in opposite to standard vertebrate synapses, the presynaptic boutons are rather large, and they have several presynaptic zones. In these zones, different types of anatomical structures are present. Some of the zones bear a so-called T-bar, a particular anatomical structure. The geometric form of the T-bar resembles the shape of the letter “T” or a table with one leg. When an action potential arises, calcium influx is triggered. The probability of vesicle docking and neurotransmitter release is superlinearly proportional to the concentration of calcium close to the vesicular release site. It is tempting to assume that the T-bar causes some sort of calcium accumulation and hence triggers a higher release probability and thus enhances neurotransmitter exocytosis. In order to study this influence in a quantitative manner, we constructed a typical T-bar geometry and compared the calcium concentration close to the active zones (AZs). We compared the case of synapses with and without T-bars. Indeed, we found a substantial influence of the T-bar structure on the presynaptic calcium concentrations close to the AZs, indicating that this anatomical structure increases vesicle release probability. Therefore, our study reveals how the T-bar zone implies a strong relation between form and function. Our study answers the question of experimental studies (namely “Wichmann and Sigrist, Journal of neurogenetics 2010”) concerning the sense of the anatomical structure of the T-bar.
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Affiliation(s)
- Markus M. Knodel
- Goethe Center for Scientific Computing (GCSC), Goethe Universität Frankfurt, Frankfurt, Germany
- *Correspondence: Markus M. Knodel ; orcid.org/0000-0001-8739-0803
| | | | - Gabriel Wittum
- Goethe Center for Scientific Computing (GCSC), Goethe Universität Frankfurt, Frankfurt, Germany
- Applied Mathematics and Computational Science, Computer, Electrical and Mathematical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
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23
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Munc13 structural transitions and oligomers that may choreograph successive stages in vesicle priming for neurotransmitter release. Proc Natl Acad Sci U S A 2022; 119:2121259119. [PMID: 35135883 PMCID: PMC8851502 DOI: 10.1073/pnas.2121259119] [Citation(s) in RCA: 34] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/21/2021] [Indexed: 12/24/2022] Open
Abstract
The speed of neural information processing in the human central nervous system is ultimately determined by the speed of chemical transmission at synapses, because action potentials have relatively short distances to traverse. The release of synaptic vesicles containing neurotransmitters must therefore be remarkably fast as compared to other forms of membrane fusion. Six separate SNARE complexes cooperate to achieve this. But how can exactly six copies be assembled under every vesicle? Here we report that six copies of the key molecular chaperone that assembles the SNAREs can arrange themselves into a closed hexagon, providing the likely answer. How can exactly six SNARE complexes be assembled under each synaptic vesicle? Here we report cryo-EM crystal structures of the core domain of Munc13, the key chaperone that initiates SNAREpin assembly. The functional core of Munc13, consisting of C1–C2B–MUN–C2C (Munc13C) spontaneously crystallizes between phosphatidylserine-rich bilayers in two distinct conformations, each in a radically different oligomeric state. In the open conformation (state 1), Munc13C forms upright trimers that link the two bilayers, separating them by ∼21 nm. In the closed conformation, six copies of Munc13C interact to form a lateral hexamer elevated ∼14 nm above the bilayer. Open and closed conformations differ only by a rigid body rotation around a flexible hinge, which when performed cooperatively assembles Munc13 into a lateral hexamer (state 2) in which the key SNARE assembly-activating site of Munc13 is autoinhibited by its neighbor. We propose that each Munc13 in the lateral hexamer ultimately assembles a single SNAREpin, explaining how only and exactly six SNARE complexes are templated. We suggest that state 1 and state 2 may represent two successive states in the synaptic vesicle supply chain leading to “primed” ready-release vesicles in which SNAREpins are clamped and ready to release (state 3).
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24
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Szule JA. Hypothesis Relating the Structure, Biochemistry and Function of Active Zone Material Macromolecules at a Neuromuscular Junction. Front Synaptic Neurosci 2022; 13:798225. [PMID: 35069169 PMCID: PMC8766674 DOI: 10.3389/fnsyn.2021.798225] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Accepted: 12/14/2021] [Indexed: 12/22/2022] Open
Abstract
This report integrates knowledge of in situ macromolecular structures and synaptic protein biochemistry to propose a unified hypothesis for the regulation of certain vesicle trafficking events (i.e., docking, priming, Ca2+-triggering, and membrane fusion) that lead to neurotransmitter secretion from specialized “active zones” of presynaptic axon terminals. Advancements in electron tomography, to image tissue sections in 3D at nanometer scale resolution, have led to structural characterizations of a network of different classes of macromolecules at the active zone, called “Active Zone Material’. At frog neuromuscular junctions, the classes of Active Zone Material macromolecules “top-masts”, “booms”, “spars”, “ribs” and “pins” direct synaptic vesicle docking while “pins”, “ribs” and “pegs” regulate priming to influence Ca2+-triggering and membrane fusion. Other classes, “beams”, “steps”, “masts”, and “synaptic vesicle luminal filaments’ likely help organize and maintain the structural integrity of active zones. Extensive studies on the biochemistry that regulates secretion have led to comprehensive characterizations of the many conserved proteins universally involved in these trafficking events. Here, a hypothesis including a partial proteomic atlas of Active Zone Material is presented which considers the common roles, binding partners, physical features/structure, and relative positioning in the axon terminal of both the proteins and classes of macromolecules involved in the vesicle trafficking events. The hypothesis designates voltage-gated Ca2+ channels and Ca2+-gated K+ channels to ribs and pegs that are connected to macromolecules that span the presynaptic membrane at the active zone. SNARE proteins (Syntaxin, SNAP25, and Synaptobrevin), SNARE-interacting proteins Synaptotagmin, Munc13, Munc18, Complexin, and NSF are designated to ribs and/or pins. Rab3A and Rabphillin-3A are designated to top-masts and/or booms and/or spars. RIM, Bassoon, and Piccolo are designated to beams, steps, masts, ribs, spars, booms, and top-masts. Spectrin is designated to beams. Lastly, the luminal portions of SV2 are thought to form the bulk of the observed synaptic vesicle luminal filaments. The goal here is to help direct future studies that aim to bridge Active Zone Material structure, biochemistry, and function to ultimately determine how it regulates the trafficking events in vivo that lead to neurotransmitter secretion.
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25
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Piao C, Sigrist SJ. (M)Unc13s in Active Zone Diversity: A Drosophila Perspective. Front Synaptic Neurosci 2022; 13:798204. [PMID: 35046788 PMCID: PMC8762327 DOI: 10.3389/fnsyn.2021.798204] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Accepted: 11/29/2021] [Indexed: 12/03/2022] Open
Abstract
The so-called active zones at pre-synaptic terminals are the ultimate filtering devices, which couple between action potential frequency and shape, and the information transferred to the post-synaptic neurons, finally tuning behaviors. Within active zones, the release of the synaptic vesicle operates from specialized “release sites.” The (M)Unc13 class of proteins is meant to define release sites topologically and biochemically, and diversity between Unc13-type release factor isoforms is suspected to steer diversity at active zones. The two major Unc13-type isoforms, namely, Unc13A and Unc13B, have recently been described from the molecular to the behavioral level, exploiting Drosophila being uniquely suited to causally link between these levels. The exact nanoscale distribution of voltage-gated Ca2+ channels relative to release sites (“coupling”) at pre-synaptic active zones fundamentally steers the release of the synaptic vesicle. Unc13A and B were found to be either tightly or loosely coupled across Drosophila synapses. In this review, we reported recent findings on diverse aspects of Drosophila Unc13A and B, importantly, their nano-topological distribution at active zones and their roles in release site generation, active zone assembly, and pre-synaptic homeostatic plasticity. We compared their stoichiometric composition at different synapse types, reviewing the correlation between nanoscale distribution of these two isoforms and release physiology and, finally, discuss how isoform-specific release components might drive the functional heterogeneity of synapses and encode discrete behavior.
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Affiliation(s)
- Chengji Piao
- Institute for Biology/Genetics, Freie Universität Berlin, Berlin, Germany
- NeuroCure Cluster of Excellence, Charité Universitätsmedizin, Berlin, Germany
| | - Stephan J. Sigrist
- Institute for Biology/Genetics, Freie Universität Berlin, Berlin, Germany
- NeuroCure Cluster of Excellence, Charité Universitätsmedizin, Berlin, Germany
- *Correspondence: Stephan J. Sigrist
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26
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You Y, Das J. Molecular dynamics simulation studies on binding of activator and inhibitor to Munc13-1 C1 in the presence of membrane. J Biomol Struct Dyn 2022; 40:14160-14175. [PMID: 34779746 PMCID: PMC9482821 DOI: 10.1080/07391102.2021.2001375] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Munc13-1 is a presynaptic active zone protein that plays a critical role in priming the synaptic vesicle and releasing neurotransmitters in the brain. Munc13-1 acts as a scaffold and is activated when diacylglycerol (DAG)/phorbol ester binds to its C1 domain in the plasma membrane. Our previous studies showed that bryostatin 1 activated the Munc13-1, but resveratrol inhibited the phorbol ester-induced Munc13-1 activity. To gain structural insights into the binding of the ligand into Munc13-1 C1 in the membrane, we conducted 1.0 μs molecular dynamics (MD) simulation on Munc13-1 C1-ligand-lipid ternary system using phorbol 13-acetate, bryostatin 1 and resveratrol as ligands. Munc13-1 C1 shows higher conformational stability and less mobility along membrane with phorbol 13-acetate and bryostatin 1 than with resveratrol. Bryostatin 1 and phorbol ester remained in the protein active site, but resveratrol moved out of Munc13-1 C1 during the MD simulation. While bryostatin 1-bound Munc13-1 C1 showed two different positioning in the membrane, phorbol 13-acetate and resveratrol-bound Munc13-1 C1 only showed one positioning. Phorbol 13-acetate formed hydrogen bond with Ala-574 and Gly-589. Bryostatin 1 had more hydrogen bonds with Trp-588 and Arg-592 than with other residues. Resveratrol formed hydrogen bond with Ile-590. This study suggests that different ligands control Munc13-1 C1's mobility and positioning in the membrane differently. Ligand also has a critical role in the interaction between Munc13-1 C1 and lipid membrane. Our results provide structural basis of the pharmacological activity of the ligands and highlight the importance of membrane in Munc13-1 activity.Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
| | - Joydip Das
- To whom to address correspondence at: Joydip Das, Department of Pharmacological and Pharmaceutical Sciences, Health 2, 4849 Calhoun Road, Room 3044, Houston TX 77204-5037. ; Tel: 713-743-1708; FAX 713-743-1229
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27
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Camacho M, Quade B, Trimbuch T, Xu J, Sari L, Rizo J, Rosenmund C. Control of neurotransmitter release by two distinct membrane-binding faces of the Munc13-1 C 1C 2B region. eLife 2021; 10:e72030. [PMID: 34779770 PMCID: PMC8648301 DOI: 10.7554/elife.72030] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Accepted: 11/14/2021] [Indexed: 11/23/2022] Open
Abstract
Munc13-1 plays a central role in neurotransmitter release through its conserved C-terminal region, which includes a diacyglycerol (DAG)-binding C1 domain, a Ca2+/PIP2-binding C2B domain, a MUN domain and a C2C domain. Munc13-1 was proposed to bridge synaptic vesicles to the plasma membrane through distinct interactions of the C1C2B region with the plasma membrane: (i) one involving a polybasic face that is expected to yield a perpendicular orientation of Munc13-1 and hinder release; and (ii) another involving the DAG-Ca2+-PIP2-binding face that is predicted to result in a slanted orientation and facilitate release. Here, we have tested this model and investigated the role of the C1C2B region in neurotransmitter release. We find that K603E or R769E point mutations in the polybasic face severely impair Ca2+-independent liposome bridging and fusion in in vitro reconstitution assays, and synaptic vesicle priming in primary murine hippocampal cultures. A K720E mutation in the polybasic face and a K706E mutation in the C2B domain Ca2+-binding loops have milder effects in reconstitution assays and do not affect vesicle priming, but enhance or impair Ca2+-evoked release, respectively. The phenotypes caused by combining these mutations are dominated by the K603E and R769E mutations. Our results show that the C1-C2B region of Munc13-1 plays a central role in vesicle priming and support the notion that two distinct faces of this region control neurotransmitter release and short-term presynaptic plasticity.
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Affiliation(s)
- Marcial Camacho
- Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of NeurophysiologyBerlinGermany
- NeuroCure Cluster of ExcellenceBerlinGermany
| | - Bradley Quade
- Department of Biophysics, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Biochemistry, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Pharmacology, University of Texas Southwestern Medical CenterDallasUnited States
| | - Thorsten Trimbuch
- Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of NeurophysiologyBerlinGermany
- NeuroCure Cluster of ExcellenceBerlinGermany
| | - Junjie Xu
- Department of Biophysics, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Biochemistry, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Pharmacology, University of Texas Southwestern Medical CenterDallasUnited States
| | - Levent Sari
- Department of Biophysics, University of Texas Southwestern Medical CenterDallasUnited States
- Cecil H. and Ida Green Comprehensive Center for Molecular, Computational and Systems Biology, University of Texas Southwestern Medical CenterDallasUnited States
- Center for Alzheimer’s and Neurodegenerative Diseases, University of Texas Southwestern Medical CenterDallasUnited States
| | - Josep Rizo
- Department of Biophysics, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Biochemistry, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Pharmacology, University of Texas Southwestern Medical CenterDallasUnited States
| | - Christian Rosenmund
- Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of NeurophysiologyBerlinGermany
- NeuroCure Cluster of ExcellenceBerlinGermany
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28
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Smejkalova T, Korinek M, Krusek J, Hrcka Krausova B, Candelas Serra M, Hajdukovic D, Kudova E, Chodounska H, Vyklicky L. Endogenous neurosteroids pregnanolone and pregnanolone sulfate potentiate presynaptic glutamate release through distinct mechanisms. Br J Pharmacol 2021; 178:3888-3904. [PMID: 33988248 PMCID: PMC8518729 DOI: 10.1111/bph.15529] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2020] [Revised: 03/23/2021] [Accepted: 05/06/2021] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND AND PURPOSE Neurosteroids influence neuronal function and have multiple promising clinical applications. Direct modulation of postsynaptic neurotransmitter receptors by neurosteroids is well characterized, but presynaptic effects remain poorly understood. Here, we report presynaptic glutamate release potentiation by neurosteroids pregnanolone and pregnanolone sulfate and compare their mechanisms of action to phorbol 12,13-dibutyrate (PDBu), a mimic of the second messenger DAG. EXPERIMENTAL APPROACH We use whole-cell patch-clamp electrophysiology and pharmacology in rat hippocampal microisland cultures and total internal reflection fluorescence (TIRF) microscopy in HEK293 cells expressing GFP-tagged vesicle priming protein Munc13-1, to explore the mechanisms of neurosteroid presynaptic modulation. KEY RESULTS Pregnanolone sulfate and pregnanolone potentiate glutamate release downstream of presynaptic Ca2+ influx, resembling the action of a phorbol ester PDBu. PDBu partially occludes the effect of pregnanolone, but not of pregnanolone sulfate. Calphostin C, an inhibitor that disrupts DAG binding to its targets, reduces the effect PDBu and pregnanolone, but not of pregnanolone sulfate, suggesting that pregnanolone might interact with a well-known DAG/phorbol ester target Munc13-1. However, TIRF microscopy experiments found no evidence of pregnanolone-induced membrane translocation of GFP-tagged Munc13-1, suggesting that pregnanolone may regulate Munc13-1 indirectly or interact with other DAG targets. CONCLUSION AND IMPLICATIONS We describe a novel presynaptic effect of neurosteroids pregnanolone and pregnanolone sulfate to potentiate glutamate release downstream of presynaptic Ca2+ influx. The mechanism of action of pregnanolone, but not of pregnanolone sulfate, partly overlaps with that of PDBu. Presynaptic effects of neurosteroids may contribute to their therapeutic potential in the treatment of disorders of the glutamate system.
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Affiliation(s)
- Tereza Smejkalova
- Institute of PhysiologyCzech Academy of SciencesPragueCzech Republic
| | - Miloslav Korinek
- Institute of PhysiologyCzech Academy of SciencesPragueCzech Republic
| | - Jan Krusek
- Institute of PhysiologyCzech Academy of SciencesPragueCzech Republic
| | | | | | | | - Eva Kudova
- Institute of Organic Chemistry and BiochemistryCzech Academy of SciencesPragueCzech Republic
| | - Hana Chodounska
- Institute of Organic Chemistry and BiochemistryCzech Academy of SciencesPragueCzech Republic
| | - Ladislav Vyklicky
- Institute of PhysiologyCzech Academy of SciencesPragueCzech Republic
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29
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Silva M, Tran V, Marty A. Calcium-dependent docking of synaptic vesicles. Trends Neurosci 2021; 44:579-592. [PMID: 34049722 DOI: 10.1016/j.tins.2021.04.003] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Revised: 02/23/2021] [Accepted: 04/09/2021] [Indexed: 10/21/2022]
Abstract
The concentration of calcium ions in presynaptic terminals regulates transmitter release, but underlying mechanisms have remained unclear. Here we review recent studies that shed new light on this issue. Fast-freezing electron microscopy and total internal reflection fluorescence microscopy studies reveal complex calcium-dependent vesicle movements including docking on a millisecond time scale. Recordings from so-called 'simple synapses' indicate that calcium not only triggers exocytosis, but also modifies synaptic strength by controlling a final, rapid vesicle maturation step before release. Molecular studies identify several calcium-sensitive domains on Munc13 and on synaptotagmin-1 that are likely involved in bringing the vesicular and plasma membranes closer together in response to calcium elevation. Together, these results suggest that calcium-dependent vesicle docking occurs in a wide range of time domains and plays a crucial role in several phenomena including synaptic facilitation, post-tetanic potentiation, and neuromodulator-induced potentiation.
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Affiliation(s)
- Melissa Silva
- Université de Paris, SPPIN-Saints Pères Paris Institute for the Neurosciences, CNRS, F-75006 Paris, France
| | - Van Tran
- Université de Paris, SPPIN-Saints Pères Paris Institute for the Neurosciences, CNRS, F-75006 Paris, France
| | - Alain Marty
- Université de Paris, SPPIN-Saints Pères Paris Institute for the Neurosciences, CNRS, F-75006 Paris, France.
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30
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You Y, Katti S, Yu B, Igumenova TI, Das J. Probing the Diacylglycerol Binding Site of Presynaptic Munc13-1. Biochemistry 2021; 60:1286-1298. [PMID: 33818064 PMCID: PMC8906797 DOI: 10.1021/acs.biochem.1c00165] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Munc13-1 is a presynaptic active zone protein that acts as a master regulator of synaptic vesicle priming and neurotransmitter release in the brain. It has been implicated in the pathophysiology of several neurodegenerative diseases. Diacylglycerol and phorbol ester activate Munc13-1 by binding to its C1 domain. The objective of this study is to identify the structural determinants of ligand binding activity of the Munc13-1 C1 domain. Molecular docking suggested that residues Trp-588, Ile-590, and Arg-592 of Munc13-1 are involved in ligand interactions. To elucidate the role of these three residues in ligand binding, we generated W588A, I590A, and R592A mutants in full-length Munc13-1, expressed them as GFP-tagged proteins in HT22 cells, and measured their ligand-induced membrane translocation by confocal microscopy and immunoblotting. The extent of 1,2-dioctanoyl-sn-glycerol (DOG)- and phorbol ester-induced membrane translocation decreased in the following order: wild type > I590A > W588A > R592A and wild type > W588A > I590A > R592A, respectively. To understand the effect of the mutations on ligand binding, we also measured the DOG binding affinity of the isolated wild-type C1 domain and its mutants in membrane-mimicking micelles using nuclear magnetic resonance methods. The DOG binding affinity decreased in the following order: wild type > I590A > R592A. No binding was detected for W588A with DOG in micelles. This study shows that Trp-588, Ile-590, and Arg-592 are essential determinants for the activity of Munc13-1 and the effects of the three residues on the activity are ligand-dependent. This study bears significance for the development of selective modulators of Munc13-1.
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Affiliation(s)
- Youngki You
- Department of Pharmacological & Pharmaceutical Sciences, College of Pharmacy, Health 2, University of Houston, Houston, Texas 77204, United States
| | - Sachin Katti
- Department of Biochemistry and Biophysics, Texas A&M University, 300 Olsen Boulevard, College Station, Texas 77843, United States
| | - Binhan Yu
- Department of Biochemistry and Biophysics, Texas A&M University, 300 Olsen Boulevard, College Station, Texas 77843, United States
| | - Tatyana I Igumenova
- Department of Biochemistry and Biophysics, Texas A&M University, 300 Olsen Boulevard, College Station, Texas 77843, United States
| | - Joydip Das
- Department of Pharmacological & Pharmaceutical Sciences, College of Pharmacy, Health 2, University of Houston, Houston, Texas 77204, United States
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31
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Nestvogel DB, Merino RM, Leon-Pinzon C, Schottdorf M, Lee C, Imig C, Brose N, Rhee JS. The Synaptic Vesicle Priming Protein CAPS-1 Shapes the Adaptation of Sensory Evoked Responses in Mouse Visual Cortex. Cell Rep 2021; 30:3261-3269.e4. [PMID: 32160535 DOI: 10.1016/j.celrep.2020.02.045] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Revised: 10/22/2019] [Accepted: 02/10/2020] [Indexed: 10/24/2022] Open
Abstract
Short-term plasticity gates information transfer across neuronal synapses and is thought to be involved in fundamental brain processes, such as cortical gain control and sensory adaptation. Neurons employ synaptic vesicle priming proteins of the CAPS and Munc13 families to shape short-term plasticity in vitro, but the relevance of this phenomenon for information processing in the intact brain is unknown. By combining sensory stimulation with in vivo patch-clamp recordings in anesthetized mice, we show that genetic deletion of CAPS-1 in thalamic neurons results in more rapid adaptation of sensory-evoked subthreshold responses in layer 4 neurons of the primary visual cortex. Optogenetic experiments in acute brain slices further reveal that the enhanced adaptation is caused by more pronounced short-term synaptic depression. Our data indicate that neurons engage CAPS-family priming proteins to shape short-term plasticity for optimal sensory information transfer between thalamic and cortical neurons in the intact brain in vivo.
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Affiliation(s)
- Dennis B Nestvogel
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany; International Max Planck Research School for Neuroscience at the University of Göttingen, 37075 Göttingen, Germany.
| | - Ricardo Martins Merino
- International Max Planck Research School for Neuroscience at the University of Göttingen, 37075 Göttingen, Germany; Theoretical Neurophysics Group, Max Planck Institute for Dynamics and Self Organization, 37077 Göttingen, Germany; Department of Molecular Biology of Neuronal Signals, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Carolina Leon-Pinzon
- Theoretical Neurophysics Group, Max Planck Institute for Dynamics and Self Organization, 37077 Göttingen, Germany; Department of Molecular Biology of Neuronal Signals, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany; Campus Institute for Dynamics of Biological Networks, 37075 Göttingen, Germany
| | - Manuel Schottdorf
- Princeton Neuroscience Institute, Princeton University, Princeton, NJ 08544, USA
| | - ChoongKu Lee
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Cordelia Imig
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Jeong-Seop Rhee
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany.
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32
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Tawfik B, Martins JS, Houy S, Imig C, Pinheiro PS, Wojcik SM, Brose N, Cooper BH, Sørensen JB. Synaptotagmin-7 places dense-core vesicles at the cell membrane to promote Munc13-2- and Ca 2+-dependent priming. eLife 2021; 10:64527. [PMID: 33749593 PMCID: PMC8012061 DOI: 10.7554/elife.64527] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Accepted: 03/19/2021] [Indexed: 12/17/2022] Open
Abstract
Synaptotagmins confer calcium-dependence to the exocytosis of secretory vesicles, but how coexpressed synaptotagmins interact remains unclear. We find that synaptotagmin-1 and synaptotagmin-7 when present alone act as standalone fast and slow Ca2+-sensors for vesicle fusion in mouse chromaffin cells. When present together, synaptotagmin-1 and synaptotagmin-7 are found in largely non-overlapping clusters on dense-core vesicles. Synaptotagmin-7 stimulates Ca2+-dependent vesicle priming and inhibits depriming, and it promotes ubMunc13-2- and phorbolester-dependent priming, especially at low resting calcium concentrations. The priming effect of synaptotagmin-7 increases the number of vesicles fusing via synaptotagmin-1, while negatively affecting their fusion speed, indicating both synergistic and competitive interactions between synaptotagmins. Synaptotagmin-7 places vesicles in close membrane apposition (<6 nm); without it, vesicles accumulate out of reach of the fusion complex (20-40 nm). We suggest that a synaptotagmin-7-dependent movement toward the membrane is involved in Munc13-2/phorbolester/Ca2+-dependent priming as a prelude to fast and slow exocytosis triggering.
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Affiliation(s)
- Bassam Tawfik
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Joana S Martins
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Sébastien Houy
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Cordelia Imig
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Paulo S Pinheiro
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark.,Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, Portugal
| | - Sonja M Wojcik
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Benjamin H Cooper
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
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33
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Liu H, Li L, Sheoran S, Yu Y, Richmond JE, Xia J, Tang J, Liu J, Hu Z. The M domain in UNC-13 regulates the probability of neurotransmitter release. Cell Rep 2021; 34:108828. [PMID: 33691106 PMCID: PMC8066380 DOI: 10.1016/j.celrep.2021.108828] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Revised: 12/25/2020] [Accepted: 02/16/2021] [Indexed: 12/30/2022] Open
Abstract
Synapses exhibit multiple forms of short-term plasticities, which have been attributed to the heterogeneity of neurotransmitter release probability. However, the molecular mechanisms that underlie the differential release states remain to be fully elucidated. The Unc-13 proteins appear to have key roles in synaptic function through multiple regulatory domains. Here, we report that deleting the M domain in Caenorhabditis elegans UNC-13MR leads to a significant increase in release probability, revealing an inhibitory function of this domain. The inhibitory effect of this domain is eliminated when the C1 and C2B domains are absent or activated, suggesting that the M domain inhibits release probability by suppressing the activity of C1 and C2B domains. When fused directly to the MUNC2C fragment of UNC-13, the M domain greatly enhances release probability. Thus, our findings reveal a mechanism by which the UNC-13 M domain regulates synaptic transmission and provides molecular insights into the regulation of release probability.
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Affiliation(s)
- Haowen Liu
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research (CJCADR), The University of Queensland, Brisbane, QLD 4072, Australia
| | - Lei Li
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research (CJCADR), The University of Queensland, Brisbane, QLD 4072, Australia
| | - Seema Sheoran
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Yi Yu
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research (CJCADR), The University of Queensland, Brisbane, QLD 4072, Australia
| | - Janet E Richmond
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Jingyao Xia
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research (CJCADR), The University of Queensland, Brisbane, QLD 4072, Australia
| | - Jing Tang
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research (CJCADR), The University of Queensland, Brisbane, QLD 4072, Australia
| | - Jie Liu
- Neuroscience Program, Monash Biomedicine Discovery Institute and Department of Anatomy and Developmental Biology, Monash University, Melbourne, VIC 3800, Australia
| | - Zhitao Hu
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research (CJCADR), The University of Queensland, Brisbane, QLD 4072, Australia.
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34
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Sundaram RVK, Jin H, Li F, Shu T, Coleman J, Yang J, Pincet F, Zhang Y, Rothman JE, Krishnakumar SS. Munc13 binds and recruits SNAP25 to chaperone SNARE complex assembly. FEBS Lett 2021; 595:297-309. [PMID: 33222163 PMCID: PMC8068094 DOI: 10.1002/1873-3468.14006] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Revised: 11/15/2020] [Accepted: 11/19/2020] [Indexed: 11/10/2022]
Abstract
Synaptic vesicle fusion is mediated by SNARE proteins-VAMP2 on the vesicle and Syntaxin-1/SNAP25 on the presynaptic membrane. Chaperones Munc18-1 and Munc13-1 cooperatively catalyze SNARE assembly via an intermediate 'template' complex containing Syntaxin-1 and VAMP2. How SNAP25 enters this reaction remains a mystery. Here, we report that Munc13-1 recruits SNAP25 to initiate the ternary SNARE complex assembly by direct binding, as judged by bulk FRET spectroscopy and single-molecule optical tweezer studies. Detailed structure-function analyses show that the binding is mediated by the Munc13-1 MUN domain and is specific for the SNAP25 'linker' region that connects the two SNARE motifs. Consequently, freely diffusing SNAP25 molecules on phospholipid bilayers are concentrated and bound in ~ 1 : 1 stoichiometry by the self-assembled Munc13-1 nanoclusters.
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Affiliation(s)
- R Venkat Kalyana Sundaram
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
| | - Huaizhou Jin
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
| | - Feng Li
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
| | - Tong Shu
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
| | - Jeff Coleman
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
| | - Jie Yang
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
| | - Frederic Pincet
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
- Laboratoire de Physique de Ecole Normale Supérieure, Université PSL, CNRS, Sorbonne Université, Université de Paris 06, F-75005 Paris, France
| | - Yongli Zhang
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
| | - James E. Rothman
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
| | - Shyam S. Krishnakumar
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
- Department of Clinical and Experimental Epilepsy, Institute of Neurology, University College London, Queens Square House, London WC1 3BG, UK
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35
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Yang CH, Lee KH, Ho WK, Lee SH. Inter-spike mitochondrial Ca 2+ release enhances high frequency synaptic transmission. J Physiol 2020; 599:1567-1594. [PMID: 33140422 DOI: 10.1113/jp280351] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2020] [Accepted: 10/27/2020] [Indexed: 01/03/2023] Open
Abstract
KEY POINTS Presynaptic mitochondria not only absorb but also release Ca2+ during high frequency stimulation (HFS) when presynaptic [Ca2+ ] is kept low (<500 nm) by high cytosolic Ca2+ buffer or strong plasma membrane calcium clearance mechanisms under physiological external [Ca2+ ]. Mitochondrial Ca2+ release (MCR) does not alter the global presynaptic Ca2+ transients. MCR during HFS enhances short-term facilitation and steady state excitatory postsynaptic currents by increasing vesicular release probability. The intra-train MCR may provide residual calcium at interspike intervals, and thus support high frequency neurotransmission at central glutamatergic synapses. ABSTRACT Emerging evidence indicates that mitochondrial Ca2+ buffering contributes to local regulation of synaptic transmission. It is unknown, however, whether mitochondrial Ca2+ release (MCR) occurs during high frequency synaptic transmission. Confirming the previous notion that 2 μm tetraphenylphosphonium (TPP+ ) is a specific inhibitor of the mitochondrial Na+ /Ca2+ exchanger (mNCX), we studied the role of MCR via mNCX in short-term plasticity during high frequency stimulation (HFS) at the calyx of Held synapse of the rat. TPP+ reduced short-term facilitation (STF) and steady state excitatory postsynaptic currents during HFS at mature calyx synapses under physiological extracellular [Ca2+ ] ([Ca2+ ]o = 1.2 mm), but not at immature calyx or at 2 mm [Ca2+ ]o . The inhibitory effects of TPP+ were stronger at synapses with morphologically complex calyces harbouring many swellings and at 32°C than at simple calyx synapses and at room temperature. These effects of TPP+ on STF were well correlated with those on the presynaptic mitochondrial [Ca2+ ] build-up during HFS. Mitochondrial [Ca2+ ] during HFS was increased by TPP+ at mature calyces under 1.2 mm [Ca2+ ]o , and further enhanced at 32°C, but not under 2 mm [Ca2+ ]o or at immature calyces. The close correlation of the effects of TPP+ on mitochondrial [Ca2+ ] with those on STF suggests that mNCX contributes to STF at the calyx of Held synapses. The intra-train MCR enhanced vesicular release probability without altering global presynaptic [Ca2+ ]. Our results suggest that MCR during HFS elevates local [Ca2+ ] near synaptic sites at interspike intervals to enhance STF and to support stable synaptic transmission under physiological [Ca2+ ]o .
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Affiliation(s)
- Che Ho Yang
- Department of Physiology, Cell Physiology Lab., Seoul National University College of Medicine and Neuroscience Research Institute, Seoul National University Medical Research Centre, Seoul, Republic of Korea
| | - Kyu-Hee Lee
- Department of Physiology, Cell Physiology Lab., Seoul National University College of Medicine and Neuroscience Research Institute, Seoul National University Medical Research Centre, Seoul, Republic of Korea
| | - Won-Kyung Ho
- Department of Physiology, Cell Physiology Lab., Seoul National University College of Medicine and Neuroscience Research Institute, Seoul National University Medical Research Centre, Seoul, Republic of Korea.,Department of Brain and Cognitive Science, Seoul National University, Seoul, Republic of Korea
| | - Suk-Ho Lee
- Department of Physiology, Cell Physiology Lab., Seoul National University College of Medicine and Neuroscience Research Institute, Seoul National University Medical Research Centre, Seoul, Republic of Korea.,Department of Brain and Cognitive Science, Seoul National University, Seoul, Republic of Korea
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36
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Disentangling the Roles of RIM and Munc13 in Synaptic Vesicle Localization and Neurotransmission. J Neurosci 2020; 40:9372-9385. [PMID: 33139401 PMCID: PMC7724145 DOI: 10.1523/jneurosci.1922-20.2020] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Revised: 09/22/2020] [Accepted: 10/15/2020] [Indexed: 11/21/2022] Open
Abstract
Efficient neurotransmitter release at the presynaptic terminal requires docking of synaptic vesicles to the active zone membrane and formation of fusion-competent synaptic vesicles near voltage-gated Ca2+ channels. Rab3-interacting molecule (RIM) is a critical active zone organizer, as it recruits Ca2+ channels and activates synaptic vesicle docking and priming via Munc13-1. However, our knowledge about Munc13-independent contributions of RIM to active zone functions is limited. To identify the functions that are solely mediated by RIM, we used genetic manipulations to control RIM and Munc13-1 activity in cultured hippocampal neurons from mice of either sex and compared synaptic ultrastructure and neurotransmission. We found that RIM modulates synaptic vesicle localization in the proximity of the active zone membrane independent of Munc13-1. In another step, both RIM and Munc13 mediate synaptic vesicle docking and priming. In addition, while the activity of both RIM and Munc13-1 is required for Ca2+-evoked release, RIM uniquely controls neurotransmitter release efficiency. However, activity-dependent augmentation of synaptic vesicle pool size relies exclusively on the action of Munc13s. Based on our results, we extend previous findings and propose a refined model in which RIM and Munc13-1 act in overlapping and independent stages of synaptic vesicle localization and release. SIGNIFICANCE STATEMENT The presynaptic active zone is composed of scaffolding proteins that functionally interact to localize synaptic vesicles to release sites, ensuring neurotransmission. Our current knowledge of the presynaptic active zone function relies on structure-function analysis, which has provided detailed information on the network of interactions and the impact of active zone proteins. Yet, the hierarchical, redundant, or independent cooperation of each active zone protein to synapse functions is not fully understood. Rab3-interacting molecule and Munc13 are the two key functionally interacting active zone proteins. Here, we dissected the distinct actions of Rab3-interacting molecule and Munc13-1 from both ultrastructural and physiological aspects. Our findings provide a more detailed view of how these two presynaptic proteins orchestrate their functions to achieve synaptic transmission.
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37
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Li L, Liu H, Hall Q, Wang W, Yu Y, Kaplan JM, Hu Z. A Hyperactive Form of unc-13 Enhances Ca 2+ Sensitivity and Synaptic Vesicle Release Probability in C. elegans. Cell Rep 2020; 28:2979-2995.e4. [PMID: 31509756 PMCID: PMC6779330 DOI: 10.1016/j.celrep.2019.08.018] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2018] [Revised: 04/22/2019] [Accepted: 07/31/2019] [Indexed: 11/26/2022] Open
Abstract
Munc13 proteins play several roles in regulating shortterm synaptic plasticity. However, the underlying molecular mechanisms remain largely unclear. Here we report that C. elegans UNC-13L, a Munc13-1 ortholog, has three domains that inhibit synaptic vesicle (SV) exocytosis. These include the X (sequence between C2A and C1), C1, and C2B domains. Deleting all three inhibitory domains produces a hyperactive UNC-13 (sUNC-13) that exhibits dramatically increased neurotransmitter release, Ca2+ sensitivity of release, and release probability. The vesicular pool in unc-13 mutants rescued by sUNC-13 exhibits a faster synaptic recovery and replenishment rate, demonstrating an important role of sUNC-13 in regulating synaptic plasticity. Analysis of double mutants suggests that sUNC-13 enhances tonic release by increasing the open probability of UNC-64/syntaxin-1A, whereas its effects on evoked release appear to be mediated by additional functions, presumably by further regulating the activity of the assembled soluble N-ethylmaleimide-sensitive factor activating protein receptor (SNARE) complex. Li et al. identify three domains in UNC-13L that inhibit neurotransmitter release. Removal of the three inhibitory domains produces a hyperactive UNC-13 that dramatically increases Ca2+ sensitivity and release probability of vesicle exocytosis by opening syntaxin in a highly efficient manner.
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Affiliation(s)
- Lei Li
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research (CJCADR), The University of Queensland, Brisbane, QLD 4072, Australia
| | - Haowen Liu
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research (CJCADR), The University of Queensland, Brisbane, QLD 4072, Australia
| | - Qi Hall
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA 02114, USA; Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Wei Wang
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research (CJCADR), The University of Queensland, Brisbane, QLD 4072, Australia
| | - Yi Yu
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research (CJCADR), The University of Queensland, Brisbane, QLD 4072, Australia
| | - Joshua M Kaplan
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA 02114, USA; Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA; Program in Neuroscience, Harvard Medical School, Boston, MA 02115, USA.
| | - Zhitao Hu
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research (CJCADR), The University of Queensland, Brisbane, QLD 4072, Australia.
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38
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Huson V, Meijer M, Dekker R, Ter Veer M, Ruiter M, van Weering JR, Verhage M, Cornelisse LN. Post-tetanic potentiation lowers the energy barrier for synaptic vesicle fusion independently of Synaptotagmin-1. eLife 2020; 9:55713. [PMID: 32831174 PMCID: PMC7500951 DOI: 10.7554/elife.55713] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Accepted: 08/23/2020] [Indexed: 11/13/2022] Open
Abstract
Previously, we showed that modulation of the energy barrier for synaptic vesicle fusion boosts release rates supralinearly (Schotten, 2015). Here we show that mouse hippocampal synapses employ this principle to trigger Ca2+-dependent vesicle release and post-tetanic potentiation (PTP). We assess energy barrier changes by fitting release kinetics in response to hypertonic sucrose. Mimicking activation of the C2A domain of the Ca2+-sensor Synaptotagmin-1 (Syt1), by adding a positive charge (Syt1D232N) or increasing its hydrophobicity (Syt14W), lowers the energy barrier. Removing Syt1 or impairing its release inhibitory function (Syt19Pro) increases spontaneous release without affecting the fusion barrier. Both phorbol esters and tetanic stimulation potentiate synaptic strength, and lower the energy barrier equally well in the presence and absence of Syt1. We propose a model where tetanic stimulation activates Syt1-independent mechanisms that lower the energy barrier and act additively with Syt1-dependent mechanisms to produce PTP by exerting multiplicative effects on release rates.
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Affiliation(s)
- Vincent Huson
- Department of Functional Genomics, Clinical Genetics, Center for Neurogenomics and Cognitive Research, Amsterdam University Medical Center- Location VUmc, Amsterdam, Netherlands
| | - Marieke Meijer
- Department of Functional Genomics, Clinical Genetics, Center for Neurogenomics and Cognitive Research, Amsterdam University Medical Center- Location VUmc, Amsterdam, Netherlands
| | - Rien Dekker
- Department of Functional Genomics, Clinical Genetics, Center for Neurogenomics and Cognitive Research, Amsterdam University Medical Center- Location VUmc, Amsterdam, Netherlands
| | - Mirelle Ter Veer
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam, Amsterdam, Netherlands
| | - Marvin Ruiter
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam, Amsterdam, Netherlands
| | - Jan Rt van Weering
- Department of Functional Genomics, Clinical Genetics, Center for Neurogenomics and Cognitive Research, Amsterdam University Medical Center- Location VUmc, Amsterdam, Netherlands
| | - Matthijs Verhage
- Department of Functional Genomics, Clinical Genetics, Center for Neurogenomics and Cognitive Research, Amsterdam University Medical Center- Location VUmc, Amsterdam, Netherlands.,Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam, Amsterdam, Netherlands
| | - Lennart Niels Cornelisse
- Department of Functional Genomics, Clinical Genetics, Center for Neurogenomics and Cognitive Research, Amsterdam University Medical Center- Location VUmc, Amsterdam, Netherlands
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39
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Vardar G, Gerth F, Schmitt XJ, Rautenstrauch P, Trimbuch T, Schubert J, Lerche H, Rosenmund C, Freund C. Epilepsy-causing STX1B mutations translate altered protein functions into distinct phenotypes in mouse neurons. Brain 2020; 143:2119-2138. [DOI: 10.1093/brain/awaa151] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2018] [Revised: 03/05/2020] [Accepted: 03/25/2020] [Indexed: 01/21/2023] Open
Abstract
AbstractSyntaxin 1B (STX1B) is a core component of the N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex that is critical for the exocytosis of synaptic vesicles in the presynapse. SNARE-mediated vesicle fusion is assisted by Munc18-1, which recruits STX1B in the auto-inhibited conformation, while Munc13 catalyses the fast and efficient pairing of helices during SNARE complex formation. Mutations within the STX1B gene are associated with epilepsy. Here we analysed three STX1B mutations by biochemical and electrophysiological means. These three paradigmatic mutations cause epilepsy syndromes of different severity, from benign fever-associated seizures in childhood to severe epileptic encephalopathies. An insertion/deletion (K45/RMCIE, L46M) mutation (STX1BInDel), causing mild epilepsy and located in the early helical Habc domain, leads to an unfolded protein unable to sustain neurotransmission. STX1BG226R, causing epileptic encephalopathies, strongly compromises the interaction with Munc18-1 and reduces expression of both proteins, the size of the readily releasable pool of vesicles, and Ca2+-triggered neurotransmitter release when expressed in STX1-null neurons. The mutation STX1BV216E, also causing epileptic encephalopathies, only slightly diminishes Munc18-1 and Munc13 interactions, but leads to enhanced fusogenicity and increased vesicular release probability, also in STX1-null neurons. Even though the synaptic output remained unchanged in excitatory hippocampal STX1B+/− neurons exogenously expressing STX1B mutants, the manifestation of clear and distinct molecular disease mechanisms by these mutants suggest that certain forms of epilepsies can be conceptualized by assigning mutations to structurally sensitive regions of the STX1B−Munc18-1 interface, translating into distinct neurophysiological phenotypes.
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Affiliation(s)
- Gülçin Vardar
- Institute of Neurophysiology, Charité-Universitätsmedizin Berlin, Germany
| | - Fabian Gerth
- Laboratory of Protein Biochemistry, Institute for Chemistry and Biochemistry, Freie Universität Berlin, Germany
| | - Xiao Jakob Schmitt
- Laboratory of Protein Biochemistry, Institute for Chemistry and Biochemistry, Freie Universität Berlin, Germany
| | - Pia Rautenstrauch
- Laboratory of Protein Biochemistry, Institute for Chemistry and Biochemistry, Freie Universität Berlin, Germany
| | - Thorsten Trimbuch
- Institute of Neurophysiology, Charité-Universitätsmedizin Berlin, Germany
| | - Julian Schubert
- Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Germany
| | - Holger Lerche
- Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Germany
| | | | - Christian Freund
- Laboratory of Protein Biochemistry, Institute for Chemistry and Biochemistry, Freie Universität Berlin, Germany
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40
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You Y, Das J. Effect of ethanol on Munc13-1 C1 in Membrane: A Molecular Dynamics Simulation Study. Alcohol Clin Exp Res 2020; 44:1344-1355. [PMID: 32424866 DOI: 10.1111/acer.14363] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2019] [Accepted: 05/06/2020] [Indexed: 12/26/2022]
Abstract
BACKGROUND EtOH has a significant effect on synaptic plasticity. Munc13-1 is an essential presynaptic active zone protein involved in priming the synaptic vesicle and releasing neurotransmitter in the brain. It is a peripheral membrane protein and binds to the activator, diacylglycerol (DAG)/phorbol ester at its membrane-targeting C1 domain. Our previous studies identified Glu-582 of C1 domain as the alcohol-binding residue (Das, J. et al, J. Neurochem., 126, 715-726, 2013). METHODS Here, we describe a 250 ns molecular dynamics (MD) simulation study on the interaction of EtOH and the activator-bound Munc13-1 C1 in the presence of varying concentrations of phosphatidylserine (PS). RESULTS In this study, Munc13-1 C1 shows higher conformational stability in EtOH than in water. It forms fewer hydrogen bonds with phorbol 13-acetate in the presence of EtOH than in water. EtOH also affected the interaction between the protein and the membrane and between the activator and the membrane. Similar studies in a E582A mutant suggest that these effects of EtOH are mostly mediated through Glu-582. CONCLUSIONS EtOH forms hydrogen bonds with Glu-582. While occupancy of the EtOH molecules at the vicinity (4Å) of Glu-582 is 34.4%, the occupancy in the E582A mutant is 26.5% of the simulation time. In addition, the amount of PS in the membrane influences the conformational stability of the C1 domain and interactions in the ternary complex. This study is important in providing the structural basis of EtOH's effects on synaptic plasticity.
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Affiliation(s)
- Youngki You
- From the Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, Texas
| | - Joydip Das
- From the Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, Texas
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41
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Bekkers JM. Autaptic Cultures: Methods and Applications. Front Synaptic Neurosci 2020; 12:18. [PMID: 32425765 PMCID: PMC7203343 DOI: 10.3389/fnsyn.2020.00018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2019] [Accepted: 04/01/2020] [Indexed: 11/13/2022] Open
Abstract
Neurons typically form daisy chains of synaptic connections with other neurons, but they can also form synapses with themselves. Although such self-synapses, or autapses, are comparatively rare in vivo, they are surprisingly common in dissociated neuronal cultures. At first glance, autapses in culture seem like a mere curiosity. However, by providing a simple model system in which a single recording electrode gives simultaneous access to the pre- and postsynaptic compartments, autaptic cultures have proven to be invaluable in facilitating important and elegant experiments in the area of synaptic neuroscience. Here, I provide detailed protocols for preparing and recording from autaptic cultures (also called micro-island or microdot cultures). Variations on the basic procedure are presented, as well as practical tips for optimizing the outcomes. I also illustrate the utility of autaptic cultures by reviewing the types of experiments that have used them over the past three decades. These examples serve to highlight the power and elegance of this simple model system, and will hopefully inspire new experiments for the interrogation of synaptic function.
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Affiliation(s)
- John M Bekkers
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research, The Australian National University, Canberra, ACT, Australia
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42
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Ruiter M, Kádková A, Scheutzow A, Malsam J, Söllner TH, Sørensen JB. An Electrostatic Energy Barrier for SNARE-Dependent Spontaneous and Evoked Synaptic Transmission. Cell Rep 2020; 26:2340-2352.e5. [PMID: 30811985 DOI: 10.1016/j.celrep.2019.01.103] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2018] [Revised: 11/05/2018] [Accepted: 01/28/2019] [Indexed: 12/22/2022] Open
Abstract
Information transfer across CNS synapses depends on the very low basal vesicle fusion rate and the ability to rapidly upregulate that rate upon Ca2+ influx. We show that local electrostatic repulsion participates in creating an energy barrier, which limits spontaneous synaptic transmission. The barrier amplitude is increased by negative charges and decreased by positive charges on the SNARE-complex surface. Strikingly, the effect of charges on the barrier is additive and this extends to evoked transmission, but with a shallower charge dependence. Action potential-driven synaptic release is equivalent to the abrupt addition of ∼35 positive charges to the fusion machine. Within an electrostatic model for triggering, the Ca2+ sensor synaptotagmin-1 contributes ∼18 charges by binding Ca2+, while also modulating the fusion barrier at rest. Thus, the energy barrier for synaptic vesicle fusion has a large electrostatic component, allowing synaptotagmin-1 to act as an electrostatic switch and modulator to trigger vesicle fusion.
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Affiliation(s)
- Marvin Ruiter
- Department of Neuroscience, Faculty of Health and Medical Sciences, 2200 Copenhagen N, University of Copenhagen, Copenhagen, Denmark
| | - Anna Kádková
- Department of Neuroscience, Faculty of Health and Medical Sciences, 2200 Copenhagen N, University of Copenhagen, Copenhagen, Denmark
| | - Andrea Scheutzow
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany
| | - Jörg Malsam
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany
| | - Thomas H Söllner
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany
| | - Jakob B Sørensen
- Department of Neuroscience, Faculty of Health and Medical Sciences, 2200 Copenhagen N, University of Copenhagen, Copenhagen, Denmark.
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43
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McCabe MP, Cullen ER, Barrows CM, Shore AN, Tooke KI, Laprade KA, Stafford JM, Weston MC. Genetic inactivation of mTORC1 or mTORC2 in neurons reveals distinct functions in glutamatergic synaptic transmission. eLife 2020; 9:e51440. [PMID: 32125271 PMCID: PMC7080408 DOI: 10.7554/elife.51440] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2019] [Accepted: 03/02/2020] [Indexed: 12/13/2022] Open
Abstract
Although mTOR signaling is known as a broad regulator of cell growth and proliferation, in neurons it regulates synaptic transmission, which is thought to be a major mechanism through which altered mTOR signaling leads to neurological disease. Although previous studies have delineated postsynaptic roles for mTOR, whether it regulates presynaptic function is largely unknown. Moreover, the mTOR kinase operates in two complexes, mTORC1 and mTORC2, suggesting that mTOR's role in synaptic transmission may be complex-specific. To better understand their roles in synaptic transmission, we genetically inactivated mTORC1 or mTORC2 in cultured mouse glutamatergic hippocampal neurons. Inactivation of either complex reduced neuron growth and evoked EPSCs (eEPSCs), however, the effects of mTORC1 on eEPSCs were postsynaptic and the effects of mTORC2 were presynaptic. Despite postsynaptic inhibition of evoked release, mTORC1 inactivation enhanced spontaneous vesicle fusion and replenishment, suggesting that mTORC1 and mTORC2 differentially modulate postsynaptic responsiveness and presynaptic release to optimize glutamatergic synaptic transmission.
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Affiliation(s)
- Matthew P McCabe
- University of Vermont, Department of Neurological SciencesBurlingtonUnited States
| | - Erin R Cullen
- University of Vermont, Department of Neurological SciencesBurlingtonUnited States
| | - Caitlynn M Barrows
- University of Vermont, Department of Neurological SciencesBurlingtonUnited States
| | - Amy N Shore
- University of Vermont, Department of Neurological SciencesBurlingtonUnited States
| | - Katherine I Tooke
- University of Vermont, Department of Neurological SciencesBurlingtonUnited States
| | - Kathryn A Laprade
- University of Vermont, Department of Neurological SciencesBurlingtonUnited States
| | - James M Stafford
- University of Vermont, Department of Neurological SciencesBurlingtonUnited States
| | - Matthew C Weston
- University of Vermont, Department of Neurological SciencesBurlingtonUnited States
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44
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Ruiter M, Houy S, Engholm-Keller K, Graham ME, Sørensen JB. SNAP-25 phosphorylation at Ser187 is not involved in Ca 2+ or phorbolester-dependent potentiation of synaptic release. Mol Cell Neurosci 2019; 102:103452. [PMID: 31794878 DOI: 10.1016/j.mcn.2019.103452] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Revised: 10/13/2019] [Accepted: 11/29/2019] [Indexed: 11/25/2022] Open
Abstract
SNAP-25, one of the three SNARE-proteins responsible for synaptic release, can be phosphorylated by Protein Kinase C on Ser-187, close to the fusion pore. In neuroendocrine cells, this phosphorylation event potentiates vesicle recruitment into releasable pools, whereas the consequences of phosphorylation for synaptic release remain unclear. We mutated Ser-187 and expressed two mutants (S187C and S187E) in the context of the SNAP-25B-isoform in SNAP-25 knockout glutamatergic autaptic neurons. Whole-cell patch clamp recordings were performed to assess the effect of Ser-187 phosphorylation on synaptic transmission. Blocking phosphorylation by expressing the S187C mutant did not affect synapse density, basic evoked or spontaneous neurotransmission, the readily-releasable pool size or its Ca2+-independent or Ca2+-dependent replenishment. Furthermore, it did not affect the response to phorbol esters, which activate PKC. Expressing S187C in the context of the SNAP-25A isoform also did not affect synaptic transmission. Strikingly, the - potentially phosphomimetic - mutant S187E reduced spontaneous release and release probability, with the largest effect seen in the SNAP-25B isoform, showing that a negative charge in this position is detrimental for neurotransmission, in agreement with electrostatic fusion triggering. During the course of our experiments, we found that higher SNAP-25B expression levels led to decreased paired pulse potentiation, probably due to higher release probabilities. Under these conditions, the potentiation of evoked EPSCs by phorbol esters was followed by a persistent down-regulation, probably due to a ceiling effect. In conclusion, our results indicate that phosphorylation of Ser-187 in SNAP-25 is not involved in modulation of synaptic release by Ca2+ or phorbol esters.
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Affiliation(s)
- Marvin Ruiter
- Department of Neuroscience, University of Copenhagen, Blegdamsvej 3C, 2200 Copenhagen N, Denmark
| | - Sébastien Houy
- Department of Neuroscience, University of Copenhagen, Blegdamsvej 3C, 2200 Copenhagen N, Denmark
| | - Kasper Engholm-Keller
- Synapse Proteomics Group, Children's Medical Research Institute, The University of Sydney, 214 Hawkesbury Road, Westmead NSW 2145, New South Wales, Australia; Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
| | - Mark E Graham
- Synapse Proteomics Group, Children's Medical Research Institute, The University of Sydney, 214 Hawkesbury Road, Westmead NSW 2145, New South Wales, Australia
| | - Jakob B Sørensen
- Department of Neuroscience, University of Copenhagen, Blegdamsvej 3C, 2200 Copenhagen N, Denmark.
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45
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Das J. SNARE Complex-Associated Proteins and Alcohol. Alcohol Clin Exp Res 2019; 44:7-18. [PMID: 31724225 DOI: 10.1111/acer.14238] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2019] [Accepted: 11/07/2019] [Indexed: 12/23/2022]
Abstract
Alcohol addiction causes major health problems throughout the world, causing numerous deaths and incurring a huge economic burden to society. To develop an intervention for alcohol addiction, it is necessary to identify molecular target(s) of alcohol and associated molecular mechanisms of alcohol action. The functions of many central and peripheral synapses are impacted by low concentrations of ethanol (EtOH). While the postsynaptic targets and mechanisms are studied extensively, there are limited studies on the presynaptic targets and mechanisms. This article is an endeavor in this direction, focusing on the effect of EtOH on the presynaptic proteins associated with the neurotransmitter release machinery. Studies on the effects of EtOH at the levels of gene, protein, and behavior are highlighted in this article.
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Affiliation(s)
- Joydip Das
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, Texas
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46
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Dong W, Radulovic T, Goral RO, Thomas C, Suarez Montesinos M, Guerrero-Given D, Hagiwara A, Putzke T, Hida Y, Abe M, Sakimura K, Kamasawa N, Ohtsuka T, Young SM. CAST/ELKS Proteins Control Voltage-Gated Ca 2+ Channel Density and Synaptic Release Probability at a Mammalian Central Synapse. Cell Rep 2019; 24:284-293.e6. [PMID: 29996090 PMCID: PMC6372087 DOI: 10.1016/j.celrep.2018.06.024] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2018] [Revised: 04/25/2018] [Accepted: 06/05/2018] [Indexed: 12/29/2022] Open
Abstract
In the presynaptic terminal, the magnitude and location of Ca2+ entry through voltage-gated Ca2+ channels (VGCCs) regulate the efficacy of neurotransmitter release. However, how presynaptic active zone proteins control mammalian VGCC levels and organization is unclear. To address this, we deleted the CAST/ELKS protein family at the calyx of Held, a CaV2.1 channel-exclusive presynaptic terminal. We found that loss of CAST/ELKS reduces the CaV2.1 current density with concomitant reductions in CaV2.1 channel numbers and clusters. Surprisingly, deletion of CAST/ELKS increases release probability while decreasing the readily releasable pool, with no change in active zone ultrastructure. In addition, Ca2+ channel coupling is unchanged, but spontaneous release rates are elevated. Thus, our data identify distinct roles for CAST/ELKS as positive regulators of CaV2.1 channel density and suggest that they regulate release probability through a post-priming step that controls synaptic vesicle fusogenicity. Dong et al. show that CAST/ELKS have multiple roles in presynaptic function. These proteins positively regulate CaV2.1 channel abundance and negatively regulate release probability. The authors propose that CAST/ELKS regulate release probability at a step in synaptic vesicle release that regulates the energy barrier for synaptic vesicle fusion.
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Affiliation(s)
- Wei Dong
- Research Group Molecular Mechanisms of Synaptic Function, Max Planck Florida Institute for Neuroscience, Jupiter, FL 33458, USA; Key Laboratory of Medical Electrophysiology, Ministry of Education, Collaborative Innovation Center for Prevention and Treatment of Cardiovascular Disease, Institute of Cardiovascular Research, Southwest Medical University, Luzhou 646000, China
| | - Tamara Radulovic
- Department of Anatomy and Cell Biology, University of Iowa, Iowa City, IA 52242, USA
| | - R Oliver Goral
- Department of Anatomy and Cell Biology, University of Iowa, Iowa City, IA 52242, USA
| | - Connon Thomas
- Max Planck Florida Institute for Neuroscience Electron Microscopy Facility, Max Planck Florida Institute for Neuroscience, Jupiter, FL 33458, USA
| | - Monica Suarez Montesinos
- Research Group Molecular Mechanisms of Synaptic Function, Max Planck Florida Institute for Neuroscience, Jupiter, FL 33458, USA
| | - Debbie Guerrero-Given
- Max Planck Florida Institute for Neuroscience Electron Microscopy Facility, Max Planck Florida Institute for Neuroscience, Jupiter, FL 33458, USA
| | - Akari Hagiwara
- Department of Biochemistry, University of Yamanashi, Yamanashi 409-3898, Japan
| | - Travis Putzke
- Research Group Molecular Mechanisms of Synaptic Function, Max Planck Florida Institute for Neuroscience, Jupiter, FL 33458, USA
| | - Yamato Hida
- Department of Biochemistry, University of Yamanashi, Yamanashi 409-3898, Japan
| | - Manabu Abe
- Department of Cellular Neurobiology, Brain Research Institute, Niigata University, Niigata 951-8585, Japan
| | - Kenji Sakimura
- Department of Cellular Neurobiology, Brain Research Institute, Niigata University, Niigata 951-8585, Japan
| | - Naomi Kamasawa
- Max Planck Florida Institute for Neuroscience Electron Microscopy Facility, Max Planck Florida Institute for Neuroscience, Jupiter, FL 33458, USA
| | - Toshihisa Ohtsuka
- Department of Biochemistry, University of Yamanashi, Yamanashi 409-3898, Japan.
| | - Samuel M Young
- Department of Anatomy and Cell Biology, University of Iowa, Iowa City, IA 52242, USA; Department of Otolaryngology, University of Iowa, Iowa City, IA 52242, USA; Iowa Neuroscience Institute, University of Iowa, Iowa City, IA 52242, USA; Aging Mind Brain Initiative, University of Iowa, Iowa City, IA 52242, USA.
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47
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Fenske P, Grauel MK, Brockmann MM, Dorrn AL, Trimbuch T, Rosenmund C. Autaptic cultures of human induced neurons as a versatile platform for studying synaptic function and neuronal morphology. Sci Rep 2019; 9:4890. [PMID: 30894602 PMCID: PMC6427022 DOI: 10.1038/s41598-019-41259-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2018] [Accepted: 03/05/2019] [Indexed: 02/08/2023] Open
Abstract
Recently developed technology to differentiate induced pluripotent stem cells (iPSCs) into human induced neurons (iNs) provides an exciting opportunity to study the function of human neurons. However, functional characterisations of iNs have been hampered by the reliance on mass culturing protocols which do not allow assessment of synaptic release characteristics and neuronal morphology at the individual cell level with quantitative precision. Here, we have developed for the first time a protocol to generate autaptic cultures of iPSC-derived iNs. We show that our method efficiently generates mature, autaptic iNs with robust spontaneous and action potential-driven synaptic transmission. The synaptic responses are sensitive to modulation by metabotropic receptor agonists as well as potentiation by acute phorbol ester application. Finally, we demonstrate loss of evoked and spontaneous release by Unc13A knockdown. This culture system provides a versatile platform allowing for quantitative and integrative assessment of morphophysiological and molecular parameters underlying human synaptic transmission.
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Affiliation(s)
- Pascal Fenske
- Institute of Neurophysiology, Charité - Universitätsmedizin, 10117, Berlin, Germany.,NeuroCure Cluster of Excellence, Charité - Universitätsmedizin, 10117, Berlin, Germany
| | - M Katharina Grauel
- Institute of Neurophysiology, Charité - Universitätsmedizin, 10117, Berlin, Germany.,NeuroCure Cluster of Excellence, Charité - Universitätsmedizin, 10117, Berlin, Germany
| | - Marisa M Brockmann
- Institute of Neurophysiology, Charité - Universitätsmedizin, 10117, Berlin, Germany.,NeuroCure Cluster of Excellence, Charité - Universitätsmedizin, 10117, Berlin, Germany
| | - Anja L Dorrn
- Institute of Neurophysiology, Charité - Universitätsmedizin, 10117, Berlin, Germany.,NeuroCure Cluster of Excellence, Charité - Universitätsmedizin, 10117, Berlin, Germany
| | - Thorsten Trimbuch
- Institute of Neurophysiology, Charité - Universitätsmedizin, 10117, Berlin, Germany.,NeuroCure Cluster of Excellence, Charité - Universitätsmedizin, 10117, Berlin, Germany
| | - Christian Rosenmund
- Institute of Neurophysiology, Charité - Universitätsmedizin, 10117, Berlin, Germany. .,NeuroCure Cluster of Excellence, Charité - Universitätsmedizin, 10117, Berlin, Germany. .,Berlin Institute of Health, Anna-Louise-Karsch-Straße 2, 10178, Berlin, Germany.
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48
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Quade B, Camacho M, Zhao X, Orlando M, Trimbuch T, Xu J, Li W, Nicastro D, Rosenmund C, Rizo J. Membrane bridging by Munc13-1 is crucial for neurotransmitter release. eLife 2019; 8:42806. [PMID: 30816091 PMCID: PMC6407922 DOI: 10.7554/elife.42806] [Citation(s) in RCA: 73] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2018] [Accepted: 02/22/2019] [Indexed: 11/13/2022] Open
Abstract
Munc13-1 plays a crucial role in neurotransmitter release. We recently proposed that the C-terminal region encompassing the C1, C2B, MUN and C2C domains of Munc13-1 (C1C2BMUNC2C) bridges the synaptic vesicle and plasma membranes through interactions involving the C2C domain and the C1-C2B region. However, the physiological relevance of this model has not been demonstrated. Here we show that C1C2BMUNC2C bridges membranes through opposite ends of its elongated structure. Mutations in putative membrane-binding sites of the C2C domain disrupt the ability of C1C2BMUNC2C to bridge liposomes and to mediate liposome fusion in vitro. These mutations lead to corresponding disruptive effects on synaptic vesicle docking, priming, and Ca2+-triggered neurotransmitter release in mouse neurons. Remarkably, these effects include an almost complete abrogation of release by a single residue substitution in this 200 kDa protein. These results show that bridging the synaptic vesicle and plasma membranes is a central function of Munc13-1.
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Affiliation(s)
- Bradley Quade
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Marcial Camacho
- Institut für Neurophysiologie, Charité - Universitätsmedizin, Berlin, Germany.,NeuroCure Cluster of Excellence, Berlin, Germany
| | - Xiaowei Zhao
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Marta Orlando
- Institut für Neurophysiologie, Charité - Universitätsmedizin, Berlin, Germany.,NeuroCure Cluster of Excellence, Berlin, Germany
| | - Thorsten Trimbuch
- Institut für Neurophysiologie, Charité - Universitätsmedizin, Berlin, Germany.,NeuroCure Cluster of Excellence, Berlin, Germany
| | - Junjie Xu
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Wei Li
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Daniela Nicastro
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Christian Rosenmund
- Institut für Neurophysiologie, Charité - Universitätsmedizin, Berlin, Germany.,NeuroCure Cluster of Excellence, Berlin, Germany
| | - Josep Rizo
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
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49
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Liu H, Li L, Nedelcu D, Hall Q, Zhou L, Wang W, Yu Y, Kaplan JM, Hu Z. Heterodimerization of UNC-13/RIM regulates synaptic vesicle release probability but not priming in C. elegans. eLife 2019; 8:40585. [PMID: 30802206 PMCID: PMC6389284 DOI: 10.7554/elife.40585] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Accepted: 02/03/2019] [Indexed: 12/17/2022] Open
Abstract
UNC-13 proteins play an essential role in synaptic transmission by recruiting synaptic vesicles (SVs) to become available for release, which is termed SV priming. Here we show that the C2A domain of UNC-13L, like the corresponding domain in mammalian Munc13-1, displays two conserved binding modes: forming C2A/C2A homodimers, or forming a heterodimer with the zinc finger domain of UNC-10/RIM (C2A/RIM). Functional analysis revealed that UNC-13L’s C2A promotes synaptic transmission by regulating a post-priming process. Stimulus-evoked release but not SV priming, was impaired in unc-10 mutants deficient for C2A/RIM heterodimerization, leading to decreased release probability. Disrupting C2A/C2A homodimerization in UNC-13L-rescued animals had no effect on synaptic transmission, but fully restored the evoked release and the release probability of unc-10/RIM mutants deficient for C2A/RIM heterodimerization. Thus, our results support the model that RIM binding C2A releases UNC-13L from an autoinhibitory homodimeric complex to become fusion-competent by functioning as a switch only.
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Affiliation(s)
- Haowen Liu
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Australia
| | - Lei Li
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Australia
| | - Daniel Nedelcu
- Department of Molecular Biology, Massachusetts General Hospital, Boston, United States.,Department of Neurobiology, Harvard Medical School, Boston, United States
| | - Qi Hall
- Department of Molecular Biology, Massachusetts General Hospital, Boston, United States.,Department of Neurobiology, Harvard Medical School, Boston, United States
| | - Lijun Zhou
- Center for Computational and Integrative Biology, Massachusetts General Hospital, Howard Hughes Medical Institute, Boston, United States
| | - Wei Wang
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Australia
| | - Yi Yu
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Australia
| | - Joshua M Kaplan
- Department of Neurobiology, Harvard Medical School, Boston, United States
| | - Zhitao Hu
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Australia
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50
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Unc13: a multifunctional synaptic marvel. Curr Opin Neurobiol 2019; 57:17-25. [PMID: 30690332 DOI: 10.1016/j.conb.2018.12.011] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2018] [Revised: 12/18/2018] [Accepted: 12/19/2018] [Indexed: 12/16/2022]
Abstract
Nervous systems are built on synaptic connections, and our understanding of these complex compartments has deepened over the past quarter century as the diverse fields of genetics, molecular biology, physiology, and biochemistry each made significant in-roads into synaptic function. On the presynaptic side, an evolutionarily conserved core fusion apparatus constructed from a handful of proteins has emerged, with Unc13 serving as a hub that coordinates nearly every aspect of synaptic transmission. This review briefly highlights recent studies on diverse aspects of Unc13 function including roles in SNARE assembly and quality control, release site building, calcium channel proximity, and short-term synaptic plasticity.
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