1
|
Agarwal A, Chandran A, Raza F, Ungureanu IM, Hilcenko C, Stott K, Bright NA, Morone N, Warren AJ, Lautenschläger J. VAMP2 regulates phase separation of α-synuclein. Nat Cell Biol 2024; 26:1296-1308. [PMID: 38951707 PMCID: PMC11322000 DOI: 10.1038/s41556-024-01451-6] [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: 07/17/2023] [Accepted: 05/30/2024] [Indexed: 07/03/2024]
Abstract
α-Synuclein (αSYN), a pivotal synaptic protein implicated in synucleinopathies such as Parkinson's disease and Lewy body dementia, undergoes protein phase separation. We reveal that vesicle-associated membrane protein 2 (VAMP2) orchestrates αSYN phase separation both in vitro and in cells. Electrostatic interactions, specifically mediated by VAMP2 via its juxtamembrane domain and the αSYN C-terminal region, drive phase separation. Condensate formation is specific for R-SNARE VAMP2 and dependent on αSYN lipid membrane binding. Our results delineate a regulatory mechanism for αSYN phase separation in cells. Furthermore, we show that αSYN condensates sequester vesicles and attract complexin-1 and -2, thus supporting a role in synaptic physiology and pathophysiology.
Collapse
Affiliation(s)
- Aishwarya Agarwal
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge Biomedical Campus, Cambridge, UK
| | - Aswathy Chandran
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge Biomedical Campus, Cambridge, UK
| | - Farheen Raza
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge Biomedical Campus, Cambridge, UK
- Protein and Cellular Sciences, GSK, Stevenage, UK
| | - Irina-Maria Ungureanu
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge Biomedical Campus, Cambridge, UK
- Department of Clinical Neurosciences, UK Dementia Research Institute, University of Cambridge, Cambridge Biomedical Campus, Cambridge, UK
| | - Christine Hilcenko
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge Biomedical Campus, Cambridge, UK
- Wellcome Trust-Medical Research Council Stem Cell Institute, Jeffrey Cheah Biomedical Centre, Cambridge Biomedical Campus, Cambridge, UK
- Department of Haematology, University of Cambridge, School of Clinical Medicine, Jeffrey Cheah Biomedical Centre, Cambridge Biomedical Campus, Cambridge, UK
| | - Katherine Stott
- Department of Biochemistry, University of Cambridge, Cambridge, UK
| | - Nicholas A Bright
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge Biomedical Campus, Cambridge, UK
| | | | - Alan J Warren
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge Biomedical Campus, Cambridge, UK
- Wellcome Trust-Medical Research Council Stem Cell Institute, Jeffrey Cheah Biomedical Centre, Cambridge Biomedical Campus, Cambridge, UK
- Department of Haematology, University of Cambridge, School of Clinical Medicine, Jeffrey Cheah Biomedical Centre, Cambridge Biomedical Campus, Cambridge, UK
| | - Janin Lautenschläger
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge Biomedical Campus, Cambridge, UK.
| |
Collapse
|
2
|
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.
Collapse
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
| |
Collapse
|
3
|
André T, van Berkel AA, Singh G, Abualrous ET, Diwan GD, Schmenger T, Braun L, Malsam J, Toonen RF, Freund C, Russell RB, Verhage M, Söllner TH. Reduced Protein Stability of 11 Pathogenic Missense STXBP1/MUNC18-1 Variants and Improved Disease Prediction. Biol Psychiatry 2024; 96:125-136. [PMID: 38490366 DOI: 10.1016/j.biopsych.2024.03.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Revised: 03/04/2024] [Accepted: 03/05/2024] [Indexed: 03/17/2024]
Abstract
BACKGROUND Pathogenic variants in STXBP1/MUNC18-1 cause severe encephalopathies that are among the most common in genetic neurodevelopmental disorders. Different molecular disease mechanisms have been proposed, and pathogenicity prediction is limited. In this study, we aimed to define a generalized disease concept for STXBP1-related disorders and improve prediction. METHODS A cohort of 11 disease-associated and 5 neutral variants (detected in healthy individuals) were tested in 3 cell-free assays and in heterologous cells and primary neurons. Protein aggregation was tested using gel filtration and Triton X-100 insolubility. PRESR (predicting STXBP1-related disorder), a machine learning algorithm that uses both sequence- and 3-dimensional structure-based features, was developed to improve pathogenicity prediction using 231 known disease-associated variants and comparison to our experimental data. RESULTS Disease-associated variants, but none of the neutral variants, produced reduced protein levels. Cell-free assays demonstrated directly that disease-associated variants have reduced thermostability, with most variants denaturing around body temperature. In addition, most disease-associated variants impaired SNARE-mediated membrane fusion in a reconstituted assay. Aggregation/insolubility was observed for none of the variants in vitro or in neurons. PRESR outperformed existing tools substantially: Matthews correlation coefficient = 0.71 versus <0.55. CONCLUSIONS These data establish intrinsic protein instability as the generalizable, primary cause for STXBP1-related disorders and show that protein-specific ortholog and 3-dimensional information improve disease prediction. PRESR is a publicly available diagnostic tool.
Collapse
Affiliation(s)
- Timon André
- Heidelberg University Biochemistry Centre, Heidelberg, Germany
| | - Annemiek A van Berkel
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Vrije Universiteit, Amsterdam, the Netherlands; Department of Clinical Genetics, Center for Neurogenomics and Cognitive Research (CNRC), University Medical Center Amsterdam; Amsterdam 1081 HV, the Netherlands
| | - Gurdeep Singh
- Heidelberg University Biochemistry Centre, Heidelberg, Germany; BioQuant, Heidelberg University, Heidelberg, Germany
| | - Esam T Abualrous
- Laboratory of Protein Biochemistry, Institute for Chemistry and Biochemistry, Freie Universität Berlin, Berlin, Germany; Department of Mathematics and Computer Science, Freie Universität Berlin, Berlin, Germany; Department of Physics, Faculty of Science, Ain Shams University, Cairo, Egypt
| | - Gaurav D Diwan
- Heidelberg University Biochemistry Centre, Heidelberg, Germany; BioQuant, Heidelberg University, Heidelberg, Germany
| | - Torsten Schmenger
- Heidelberg University Biochemistry Centre, Heidelberg, Germany; BioQuant, Heidelberg University, Heidelberg, Germany
| | - Lara Braun
- Heidelberg University Biochemistry Centre, Heidelberg, Germany
| | - Jörg Malsam
- Heidelberg University Biochemistry Centre, Heidelberg, Germany
| | - Ruud F Toonen
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Vrije Universiteit, Amsterdam, the Netherlands
| | - Christian Freund
- Laboratory of Protein Biochemistry, Institute for Chemistry and Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Robert B Russell
- Heidelberg University Biochemistry Centre, Heidelberg, Germany; BioQuant, Heidelberg University, Heidelberg, Germany
| | - Matthijs Verhage
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Vrije Universiteit, Amsterdam, the Netherlands; Department of Clinical Genetics, Center for Neurogenomics and Cognitive Research (CNRC), University Medical Center Amsterdam; Amsterdam 1081 HV, the Netherlands.
| | | |
Collapse
|
4
|
Amos C, Kiessling V, Kreutzberger AJB, Schenk NA, Mohan R, Nyenhuis S, Doyle CA, Wang HY, Levental K, Levental I, Anantharam A, Tamm LK. Membrane lipids couple synaptotagmin to SNARE-mediated granule fusion in insulin-secreting cells. Mol Biol Cell 2024; 35:ar12. [PMID: 38117594 PMCID: PMC10916878 DOI: 10.1091/mbc.e23-06-0225] [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] [Received: 06/12/2023] [Revised: 12/04/2023] [Accepted: 12/14/2023] [Indexed: 12/22/2023] Open
Abstract
Insulin secretion depends on the Ca2+-regulated fusion of granules with the plasma membrane. A recent model of Ca2+-triggered exocytosis in secretory cells proposes that lipids in the plasma membrane couple the calcium sensor Syt1 to the membrane fusion machinery (Kiessling et al., 2018). Specifically, Ca2+-mediated binding of Syt1's C2 domains to the cell membrane shifts the membrane-anchored SNARE syntaxin-1a to a more fusogenic conformation, straightening its juxtamembrane linker. To test this model in live cells and extend it to insulin secretion, we enriched INS1 cells with a panel of lipids with different acyl chain compositions. Fluorescence lifetime measurements demonstrate that cells with more disordered membranes show an increase in fusion efficiency, and vice versa. Experiments with granules purified from INS1 cells and recombinant SNARE proteins reconstituted in supported membranes confirmed that lipid acyl chain composition determines SNARE conformation and that lipid disordering correlates with increased fusion. Addition of Syt1's C2AB domains significantly decreased lipid order in target membranes and increased SNARE-mediated fusion probability. Strikingly, Syt's action on both fusion and lipid order could be partially bypassed by artificially increasing unsaturated phosphatidylserines in the target membrane. Thus, plasma membrane lipids actively participate in coupling Ca2+/synaptotagmin-sensing to the SNARE fusion machinery in cells.
Collapse
Affiliation(s)
- Chase Amos
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA 22908
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22908
| | - Volker Kiessling
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA 22908
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22908
| | - Alex J. B. Kreutzberger
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA 22908
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22908
| | - Noah A. Schenk
- Department of Neurosciences, University of Toledo, Toledo, OH 43614
| | - Ramkumar Mohan
- Department of Neurosciences, University of Toledo, Toledo, OH 43614
| | - Sarah Nyenhuis
- Department of Chemistry, University of Virginia, Charlottesville, VA, 22904
| | - Catherine A. Doyle
- Department of Pharmacology, University of Virginia Health System, Charlottesville, VA 22908
| | - Hong-Yin Wang
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA 22908
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22908
| | - Kandice Levental
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA 22908
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22908
| | - Ilya Levental
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA 22908
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22908
| | - Arun Anantharam
- Department of Neurosciences, University of Toledo, Toledo, OH 43614
| | - Lukas K. Tamm
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA 22908
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22908
| |
Collapse
|
5
|
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.
Collapse
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
| | | | | |
Collapse
|
6
|
Jahn R, Cafiso DC, Tamm LK. Mechanisms of SNARE proteins in membrane fusion. Nat Rev Mol Cell Biol 2024; 25:101-118. [PMID: 37848589 DOI: 10.1038/s41580-023-00668-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/06/2023] [Indexed: 10/19/2023]
Abstract
Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are a family of small conserved eukaryotic proteins that mediate membrane fusion between organelles and with the plasma membrane. SNAREs are directly or indirectly anchored to membranes. Prior to fusion, complementary SNAREs assemble between membranes with the aid of accessory proteins that provide a scaffold to initiate SNARE zippering, pulling the membranes together and mediating fusion. Recent advances have enabled the construction of detailed models describing bilayer transitions and energy barriers along the fusion pathway and have elucidated the structures of SNAREs complexed in various states with regulatory proteins. In this Review, we discuss how these advances are yielding an increasingly detailed picture of the SNARE-mediated fusion pathway, leading from first contact between the membranes via metastable non-bilayer intermediates towards the opening and expansion of a fusion pore. We describe how SNARE proteins assemble into complexes, how this assembly is regulated by accessory proteins and how SNARE complexes overcome the free energy barriers that prevent spontaneous membrane fusion.
Collapse
Affiliation(s)
- Reinhard Jahn
- Laboratory of Neurobiology, Max-Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.
| | - David C Cafiso
- Department of Chemistry, University of Virginia, Charlottesville, VA, USA
| | - Lukas K Tamm
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| |
Collapse
|
7
|
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.
Collapse
|
8
|
Abstract
Major recent advances and previous data have led to a plausible model of how key proteins mediate neurotransmitter release. In this model, the soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) receptor (SNARE) proteins syntaxin-1, SNAP-25, and synaptobrevin form tight complexes that bring the membranes together and are crucial for membrane fusion. NSF and SNAPs disassemble SNARE complexes and ensure that fusion occurs through an exquisitely regulated pathway that starts with Munc18-1 bound to a closed conformation of syntaxin-1. Munc18-1 also binds to synaptobrevin, forming a template to assemble the SNARE complex when Munc13-1 opens syntaxin-1 while bridging the vesicle and plasma membranes. Synaptotagmin-1 and complexin bind to partially assembled SNARE complexes, likely stabilizing them and preventing fusion until Ca2+ binding to synaptotagmin-1 causes dissociation from the SNARE complex and induces interactions with phospholipids that help trigger release. Although fundamental questions remain about the mechanism of membrane fusion, these advances provide a framework to investigate the mechanisms underlying presynaptic plasticity.
Collapse
Affiliation(s)
- Josep Rizo
- Departments of Biophysics, Biochemistry, and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, USA;
| |
Collapse
|
9
|
The complexin C-terminal amphipathic helix stabilizes the fusion pore open state by sculpting membranes. Nat Struct Mol Biol 2022; 29:97-107. [DOI: 10.1038/s41594-021-00716-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2021] [Accepted: 12/14/2021] [Indexed: 12/13/2022]
|
10
|
Zhang W, Khan A, Vitale J, Neuner A, Rink K, Lüchtenborg C, Brügger B, Söllner TH, Schiebel E. A short perinuclear amphipathic α-helix in Apq12 promotes nuclear pore complex biogenesis. Open Biol 2021; 11:210250. [PMID: 34814743 PMCID: PMC8611336 DOI: 10.1098/rsob.210250] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The integral membrane protein Apq12 is an important nuclear envelope (NE)/endoplasmic reticulum (ER) modulator that cooperates with the nuclear pore complex (NPC) biogenesis factors Brl1 and Brr6. How Apq12 executes these functions is unknown. Here, we identified a short amphipathic α-helix (AαH) in Apq12 that links the two transmembrane domains in the perinuclear space and has liposome-binding properties. Cells expressing an APQ12 (apq12-ah) version in which AαH is disrupted show NPC biogenesis and NE integrity defects, without impacting Apq12-ah topology or NE/ER localization. Overexpression of APQ12 but not apq12-ah triggers striking over-proliferation of the outer nuclear membrane (ONM)/ER and promotes accumulation of phosphatidic acid (PA) at the NE. Apq12 and Apq12-ah both associate with NPC biogenesis intermediates and removal of AαH increases both Brl1 levels and the interaction between Brl1 and Brr6. We conclude that the short amphipathic α-helix of Apq12 regulates the function of Brl1 and Brr6 and promotes PA accumulation at the NE possibly during NPC biogenesis.
Collapse
Affiliation(s)
- Wanlu Zhang
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany
| | - Azqa Khan
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany
| | - Jlenia Vitale
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany
| | - Annett Neuner
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany
| | - Kerstin Rink
- Biochemie-Zentrum der Universität Heidelberg, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
| | - Christian Lüchtenborg
- Biochemie-Zentrum der Universität Heidelberg, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
| | - Britta Brügger
- Biochemie-Zentrum der Universität Heidelberg, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
| | - Thomas H. Söllner
- Biochemie-Zentrum der Universität Heidelberg, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany
| | - Elmar Schiebel
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany
| |
Collapse
|
11
|
Sauvola CW, Littleton JT. SNARE Regulatory Proteins in Synaptic Vesicle Fusion and Recycling. Front Mol Neurosci 2021; 14:733138. [PMID: 34421538 PMCID: PMC8377282 DOI: 10.3389/fnmol.2021.733138] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Accepted: 07/20/2021] [Indexed: 01/01/2023] Open
Abstract
Membrane fusion is a universal feature of eukaryotic protein trafficking and is mediated by the soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) family. SNARE proteins embedded in opposing membranes spontaneously assemble to drive membrane fusion and cargo exchange in vitro. Evolution has generated a diverse complement of SNARE regulatory proteins (SRPs) that ensure membrane fusion occurs at the right time and place in vivo. While a core set of SNAREs and SRPs are common to all eukaryotic cells, a specialized set of SRPs within neurons confer additional regulation to synaptic vesicle (SV) fusion. Neuronal communication is characterized by precise spatial and temporal control of SNARE dynamics within presynaptic subdomains specialized for neurotransmitter release. Action potential-elicited Ca2+ influx at these release sites triggers zippering of SNAREs embedded in the SV and plasma membrane to drive bilayer fusion and release of neurotransmitters that activate downstream targets. Here we discuss current models for how SRPs regulate SNARE dynamics and presynaptic output, emphasizing invertebrate genetic findings that advanced our understanding of SRP regulation of SV cycling.
Collapse
Affiliation(s)
- Chad W Sauvola
- The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States
| | - J Troy Littleton
- The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States.,Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, United States
| |
Collapse
|
12
|
Borchers AC, Langemeyer L, Ungermann C. Who's in control? Principles of Rab GTPase activation in endolysosomal membrane trafficking and beyond. J Cell Biol 2021; 220:212549. [PMID: 34383013 PMCID: PMC8366711 DOI: 10.1083/jcb.202105120] [Citation(s) in RCA: 68] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Revised: 07/08/2021] [Accepted: 07/08/2021] [Indexed: 12/12/2022] Open
Abstract
The eukaryotic endomembrane system consists of multiple interconnected organelles. Rab GTPases are organelle-specific markers that give identity to these membranes by recruiting transport and trafficking proteins. During transport processes or along organelle maturation, one Rab is replaced by another, a process termed Rab cascade, which requires at its center a Rab-specific guanine nucleotide exchange factor (GEF). The endolysosomal system serves here as a prime example for a Rab cascade. Along with endosomal maturation, the endosomal Rab5 recruits and activates the Rab7-specific GEF Mon1-Ccz1, resulting in Rab7 activation on endosomes and subsequent fusion of endosomes with lysosomes. In this review, we focus on the current idea of Mon1-Ccz1 recruitment and activation in the endolysosomal and autophagic pathway. We compare identified principles to other GTPase cascades on endomembranes, highlight the importance of regulation, and evaluate in this context the strength and relevance of recent developments in in vitro analyses to understand the underlying foundation of organelle biogenesis and maturation.
Collapse
Affiliation(s)
- Ann-Christin Borchers
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
| | - Lars Langemeyer
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
| | - Christian Ungermann
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany.,Center of Cellular Nanoanalytics Osnabrück (CellNanOs), Osnabrück University, Osnabrück, Germany
| |
Collapse
|
13
|
Complexin Suppresses Spontaneous Exocytosis by Capturing the Membrane-Proximal Regions of VAMP2 and SNAP25. Cell Rep 2021; 32:107926. [PMID: 32698012 PMCID: PMC7116205 DOI: 10.1016/j.celrep.2020.107926] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2019] [Revised: 02/28/2020] [Accepted: 06/26/2020] [Indexed: 01/29/2023] Open
Abstract
The neuronal protein complexin contains multiple domains that exert clamping and facilitatory functions to tune spontaneous and action potential-triggered synaptic release. We address the clamping mechanism and show that the accessory helix of complexin arrests assembly of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex that forms the core machinery of intracellular membrane fusion. In a reconstituted fusion assay, site-and stage-specific photo-cross-linking reveals that, prior to fusion, the complexin accessory helix laterally binds the membrane-proximal C-terminal ends of SNAP25 and VAMP2. Corresponding complexin interface mutants selectively increase spontaneous release of neuro-transmitters in living neurons, implying that the accessory helix suppresses final zippering/assembly of the SNARE four-helix bundle by restraining VAMP2 and SNAP25.
Collapse
|
14
|
André T, Classen J, Brenner P, Betts MJ, Dörr B, Kreye S, Zuidinga B, Meijer M, Russell RB, Verhage M, Söllner TH. The Interaction of Munc18-1 Helix 11 and 12 with the Central Region of the VAMP2 SNARE Motif Is Essential for SNARE Templating and Synaptic Transmission. eNeuro 2020; 7:ENEURO.0278-20.2020. [PMID: 33055194 PMCID: PMC7768276 DOI: 10.1523/eneuro.0278-20.2020] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2020] [Revised: 08/13/2020] [Accepted: 08/24/2020] [Indexed: 01/11/2023] Open
Abstract
Sec1/Munc18 proteins play a key role in initiating the assembly of N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes, the molecular fusion machinery. Employing comparative structure modeling, site specific crosslinking by single amino acid substitutions with the photoactivatable unnatural amino acid p-Benzoyl-phenylalanine (Bpa) and reconstituted vesicle docking/fusion assays, we mapped the binding interface between Munc18-1 and the neuronal v-SNARE VAMP2 with single amino acid resolution. Our results show that helices 11 and 12 of domain 3a in Munc18-1 interact with the VAMP2 SNARE motif covering the region from layers -4 to +5. Residue Q301 in helix 11 plays a pivotal role in VAMP2 binding and template complex formation. A VAMP2 binding deficient mutant, Munc18-1 Q301D, does not stimulate lipid mixing in a reconstituted fusion assay. The neuronal SNARE-organizer Munc13-1, which also binds VAMP2, does not bypass the requirement for the Munc18-1·VAMP2 interaction. Importantly, Munc18-1 Q301D expression in Munc18-1 deficient neurons severely reduces synaptic transmission, demonstrating the physiological significance of the Munc18-1·VAMP2 interaction.
Collapse
Affiliation(s)
- Timon André
- Heidelberg University Biochemistry Center, Heidelberg 69120, Germany
| | | | - Philipp Brenner
- Heidelberg University Biochemistry Center, Heidelberg 69120, Germany
| | - Matthew J Betts
- Heidelberg University Biochemistry Center, Heidelberg 69120, Germany
- BioQuant, Heidelberg University, Heidelberg 69120, Germany
| | - Bernhard Dörr
- Heidelberg University Biochemistry Center, Heidelberg 69120, Germany
| | - Susanne Kreye
- Heidelberg University Biochemistry Center, Heidelberg 69120, Germany
| | | | - Marieke Meijer
- Clinical Genetics, Center for Neurogenomics and Cognitive Research (CNCR) Amsterdam Neuroscience, VU University and University Medical Center Amsterdam (UMCA), Amsterdam 1081HV, The Netherlands
| | - Robert B Russell
- Heidelberg University Biochemistry Center, Heidelberg 69120, Germany
- BioQuant, Heidelberg University, Heidelberg 69120, Germany
| | - Matthijs Verhage
- Department of Functional Genomics
- Clinical Genetics, Center for Neurogenomics and Cognitive Research (CNCR) Amsterdam Neuroscience, VU University and University Medical Center Amsterdam (UMCA), Amsterdam 1081HV, The Netherlands
| | - Thomas H Söllner
- Heidelberg University Biochemistry Center, Heidelberg 69120, Germany
| |
Collapse
|
15
|
Ginger L, Malsam J, Sonnen AFP, Morado D, Scheutzow A, Söllner TH, Briggs JAG. Arrangements of proteins at reconstituted synaptic vesicle fusion sites depend on membrane separation. FEBS Lett 2020; 594:3450-3463. [PMID: 32860428 PMCID: PMC7711843 DOI: 10.1002/1873-3468.13916] [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: 04/30/2020] [Revised: 07/16/2020] [Accepted: 08/09/2020] [Indexed: 11/18/2022]
Abstract
Synaptic vesicle proteins, including N‐ethylmaleimide‐sensitive factor attachment protein receptors (SNAREs), Synaptotagmin‐1 and Complexin, are responsible for controlling the synchronised fusion of synaptic vesicles with the presynaptic plasma membrane in response to elevated cytosolic calcium levels. A range of structures of SNAREs and their regulatory proteins have been elucidated, but the exact organisation of these proteins at synaptic junction membranes remains elusive. Here, we have used cryoelectron tomography to investigate the arrangement of synaptic proteins in an in vitro reconstituted fusion system. We found that the separation between vesicle and target membranes strongly correlates with the organisation of protein complexes at junctions. At larger membrane separations, protein complexes assume a ‘clustered’ distribution at the docking site, inducing a protrusion in the target membrane. As the membrane separation decreases, protein complexes become displaced radially outwards and assume a ‘ring‐like’ arrangement. Our findings indicate that docked vesicles can possess a wide range of protein complex numbers and be heterogeneous in their protein arrangements.
Collapse
Affiliation(s)
- Lucy Ginger
- MRC Laboratory of Molecular Biology, Cambridge, UK
| | - Joerg Malsam
- Heidelberg University Biochemistry Center, Heidelberg, Germany
| | - Andreas F-P Sonnen
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | | | | | | | - John A G Briggs
- MRC Laboratory of Molecular Biology, Cambridge, UK.,Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| |
Collapse
|
16
|
Brod J, Hellwig A, Wieland FT. Epsin but not AP-2 supports reconstitution of endocytic clathrin-coated vesicles. FEBS Lett 2020; 594:2227-2239. [PMID: 32337703 DOI: 10.1002/1873-3468.13801] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Revised: 04/05/2020] [Accepted: 04/10/2020] [Indexed: 12/12/2022]
Abstract
Formation of clathrin-coated vesicles (CCVs) in receptor-mediated endocytosis is a mechanistically well-established process, in which clathrin, the adaptor protein complex AP-2, and the large GTPase dynamin play crucial roles. In order to obtain more mechanistic insight into this process, here we established a giant unilamellar vesicle (GUV)-based in vitro CCV reconstitution system with chemically defined components and the full-length recombinant proteins clathrin, AP-2, epsin-1, and dynamin-2. Our results support the predominant model in which hydrolysis of GTP by dynamin is a prerequisite to generate CCVs. Strikingly, in this system at near physiological concentrations of reagents, epsin-1 alone does not have the propensity for scission but is required for bud formation, whereas AP-2 and clathrin are not sufficient. Thus, our study reveals that epsin-1 is an important factor for the maturation of clathrin coated buds, a prerequisite for vesicle generation.
Collapse
Affiliation(s)
- Jan Brod
- Heidelberg University Biochemistry Center (BZH), University of Heidelberg, Germany
| | - Andrea Hellwig
- Interdisciplinary Center for Neurosciences (IZN), University of Heidelberg, Germany
| | - Felix T Wieland
- Heidelberg University Biochemistry Center (BZH), University of Heidelberg, Germany
| |
Collapse
|
17
|
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: 15] [Impact Index Per Article: 3.8] [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.
Collapse
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.
| |
Collapse
|
18
|
In vitro fusion of single synaptic and dense core vesicles reproduces key physiological properties. Nat Commun 2019; 10:3904. [PMID: 31467284 PMCID: PMC6715626 DOI: 10.1038/s41467-019-11873-8] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Accepted: 08/02/2019] [Indexed: 12/29/2022] Open
Abstract
Regulated exocytosis of synaptic vesicles is substantially faster than of endocrine dense core vesicles despite similar molecular machineries. The reasons for this difference are unknown and could be due to different regulatory proteins, different spatial arrangements, different vesicle sizes, or other factors. To address these questions, we take a reconstitution approach and compare regulated SNARE-mediated fusion of purified synaptic and dense core chromaffin and insulin vesicles using a single vesicle-supported membrane fusion assay. In all cases, Munc18 and complexin are required to restrict fusion in the absence of calcium. Calcium triggers fusion of all docked vesicles. Munc13 (C1C2MUN domain) is required for synaptic and enhanced insulin vesicle fusion, but not for chromaffin vesicles, correlating inversely with the presence of CAPS protein on purified vesicles. Striking disparities in calcium-triggered fusion rates are observed, increasing with curvature with time constants 0.23 s (synaptic vesicles), 3.3 s (chromaffin vesicles), and 9.1 s (insulin vesicles) and correlating with rate differences in cells.
Collapse
|
19
|
Coleman J, Jouannot O, Ramakrishnan SK, Zanetti MN, Wang J, Salpietro V, Houlden H, Rothman JE, Krishnakumar SS. PRRT2 Regulates Synaptic Fusion by Directly Modulating SNARE Complex Assembly. Cell Rep 2019; 22:820-831. [PMID: 29346777 PMCID: PMC5792450 DOI: 10.1016/j.celrep.2017.12.056] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2017] [Revised: 11/12/2017] [Accepted: 12/17/2017] [Indexed: 11/25/2022] Open
Abstract
Mutations in proline-rich transmembrane protein 2 (PRRT2) are associated with a range of paroxysmal neurological disorders. PRRT2 predominantly localizes to the pre-synaptic terminals and is believed to regulate neurotransmitter release. However, the mechanism of action is unclear. Here, we use reconstituted single vesicle and bulk fusion assays, combined with live cell imaging of single exocytotic events in PC12 cells and biophysical analysis, to delineate the physiological role of PRRT2. We report that PRRT2 selectively blocks the trans SNARE complex assembly and thus negatively regulates synaptic vesicle priming. This inhibition is actualized via weak interactions of the N-terminal proline-rich domain with the synaptic SNARE proteins. Furthermore, we demonstrate that paroxysmal dyskinesia-associated mutations in PRRT2 disrupt this SNARE-modulatory function and with efficiencies corresponding to the severity of the disease phenotype. Our findings provide insights into the molecular mechanisms through which loss-of-function mutations in PRRT2 result in paroxysmal neurological disorders.
Collapse
Affiliation(s)
- Jeff Coleman
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Ouardane Jouannot
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Sathish K Ramakrishnan
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Maria N Zanetti
- Department of Clinical and Experimental Epilepsy, University College London, London WC1N 3BG, UK
| | - Jing Wang
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Vincenzo Salpietro
- Department of Molecular Neuroscience, Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Henry Houlden
- Department of Molecular Neuroscience, Institute of Neurology, University College London, London WC1N 3BG, UK
| | - James E Rothman
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA; Department of Clinical and Experimental Epilepsy, University College London, London WC1N 3BG, UK.
| | - Shyam S Krishnakumar
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA; Department of Clinical and Experimental Epilepsy, University College London, London WC1N 3BG, UK.
| |
Collapse
|
20
|
Grushin K, Wang J, Coleman J, Rothman JE, Sindelar CV, Krishnakumar SS. Structural basis for the clamping and Ca 2+ activation of SNARE-mediated fusion by synaptotagmin. Nat Commun 2019; 10:2413. [PMID: 31160571 PMCID: PMC6546687 DOI: 10.1038/s41467-019-10391-x] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Accepted: 05/08/2019] [Indexed: 12/22/2022] Open
Abstract
Synapotagmin-1 (Syt1) interacts with both SNARE proteins and lipid membranes to synchronize neurotransmitter release to calcium (Ca2+) influx. Here we report the cryo-electron microscopy structure of the Syt1-SNARE complex on anionic-lipid containing membranes. Under resting conditions, the Syt1 C2 domains bind the membrane with a magnesium (Mg2+)-mediated partial insertion of the aliphatic loops, alongside weak interactions with the anionic lipid headgroups. The C2B domain concurrently interacts the SNARE bundle via the 'primary' interface and is positioned between the SNAREpins and the membrane. In this configuration, Syt1 is projected to sterically delay the complete assembly of the associated SNAREpins and thus, contribute to clamping fusion. This Syt1-SNARE organization is disrupted upon Ca2+-influx as Syt1 reorients into the membrane, likely displacing the attached SNAREpins and reversing the fusion clamp. We thus conclude that the cation (Mg2+/Ca2+) dependent membrane interaction is a key determinant of the dual clamp/activator function of Synaptotagmin-1.
Collapse
Affiliation(s)
- Kirill Grushin
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT, 06520, USA
| | - Jing Wang
- 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
| | - James E Rothman
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT, 06520, USA
| | - Charles V Sindelar
- Department of Molecular Biophysics and Biochemistry, 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.
| |
Collapse
|
21
|
Abstract
Ca2+-dependent secretion is a process by which important signaling molecules that are produced within a cell-including proteins and neurotransmitters-are expelled to the extracellular environment. The cellular mechanism that underlies secretion is referred to as exocytosis. Many years of work have revealed that exocytosis in neurons and neuroendocrine cells is tightly coupled to Ca2+ and orchestrated by a series of protein-protein/protein-lipid interactions. Here, we highlight landmark discoveries that have informed our current understanding of the process. We focus principally on reductionist studies performed using powerful model secretory systems and cell-free reconstitution assays. In recent years, molecular cloning and genetics have implicated the involvement of a sizeable number of proteins in exocytosis. We expect reductionist approaches will be central to attempts to resolve their roles. The Journal of General Physiology will continue to be an outlet for much of this work, befitting its tradition of publishing strongly mechanistic, basic research.
Collapse
Affiliation(s)
- Arun Anantharam
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| | - Alex J B Kreutzberger
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA
| |
Collapse
|
22
|
Biomechanical characterization of TIM protein-mediated Ebola virus-host cell adhesion. Sci Rep 2019; 9:267. [PMID: 30670766 PMCID: PMC6342996 DOI: 10.1038/s41598-018-36449-2] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2018] [Accepted: 11/21/2018] [Indexed: 01/19/2023] Open
Abstract
Since the most recent outbreak, the Ebola virus (EBOV) epidemic remains one of the world’s public health and safety concerns. EBOV is a negative-sense RNA virus that can infect humans and non-human primates, and causes hemorrhagic fever. It has been proposed that the T-cell immunoglobulin and mucin domain (TIM) family proteins act as cell surface receptors for EBOV, and that the interaction between TIM and phosphatidylserine (PS) on the surface of EBOV mediates the EBOV–host cell attachment. Despite these initial findings, the biophysical properties of the TIM-EBOV interaction, such as the mechanical strength of the TIM-PS bond that allows the virus-cell interaction to resist external mechanical perturbations, have not yet been characterized. This study utilizes single-molecule force spectroscopy to quantify the specific interaction forces between TIM-1 or TIM-4 and the following binding partners: PS, EBOV virus-like particle, and EBOV glycoprotein/vesicular stomatitis virus pseudovirion. Depending on the loading rates, the unbinding forces between TIM and ligands ranged from 40 to 100 pN, suggesting that TIM-EBOV interactions are mechanically comparable to previously reported adhesion molecule–ligand interactions. The TIM-4–PS interaction is more resistant to mechanical force than the TIM-1–PS interaction. We have developed a simple model for virus–host cell interaction that is driven by its adhesion to cell surface receptors and resisted by membrane bending (or tension). Our model identifies critical dimensionless parameters representing the ratio of deformation and adhesion energies, showing how single-molecule adhesion measurements relate quantitatively to the mechanics of virus adhesion to the cell.
Collapse
|
23
|
Ramakrishnan S, Bera M, Coleman J, Krishnakumar SS, Pincet F, Rothman JE. Synaptotagmin oligomers are necessary and can be sufficient to form a Ca 2+ -sensitive fusion clamp. FEBS Lett 2019; 593:154-162. [PMID: 30570144 PMCID: PMC6349546 DOI: 10.1002/1873-3468.13317] [Citation(s) in RCA: 35] [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: 12/04/2018] [Revised: 12/16/2018] [Accepted: 12/17/2018] [Indexed: 12/11/2022]
Abstract
The buttressed‐ring hypothesis, supported by recent cryo‐electron tomography analysis of docked synaptic‐like vesicles in neuroendocrine cells, postulates that prefusion SNAREpins are stabilized and organized by Synaptotagmin (Syt) ring‐like oligomers. Here, we use a reconstituted single‐vesicle fusion analysis to test the prediction that destabilizing the Syt1 oligomers destabilizes the clamp and results in spontaneous fusion in the absence of Ca2+. Vesicles in which Syt oligomerization is compromised by a ring‐destabilizing mutation dock and diffuse freely on the bilayer until they fuse spontaneously, similar to vesicles containing only v‐SNAREs. In contrast, vesicles containing wild‐type Syt are immobile as soon as they attach to the bilayer and remain frozen in place, up to at least 1 h until fusion is triggered by Ca2+.
Collapse
Affiliation(s)
| | - Manindra Bera
- Department of Cell BiologyYale University School of MedicineNew HavenCTUSA
| | - Jeff Coleman
- Department of Cell BiologyYale University School of MedicineNew HavenCTUSA
| | - Shyam S. Krishnakumar
- Department of Cell BiologyYale University School of MedicineNew HavenCTUSA
- Department of Clinical and Experimental EpilepsyUCL Queen Square Institute of NeurologyLondonUK
| | - Frederic Pincet
- Department of Cell BiologyYale University School of MedicineNew HavenCTUSA
- Laboratoire de Physique StatistiqueEcole Normale SupérieureSorbonne Universités UPMC Univ Paris 06, CNRSPSL Research UniversityUniversité Paris Diderot Sorbonne Paris CitéFrance
| | - James E. Rothman
- Department of Cell BiologyYale University School of MedicineNew HavenCTUSA
- Department of Clinical and Experimental EpilepsyUCL Queen Square Institute of NeurologyLondonUK
| |
Collapse
|
24
|
Ma L, Jiao J, Zhang Y. Single-Molecule Optical Tweezers Study of Regulated SNARE Assembly. Methods Mol Biol 2019; 1860:95-114. [PMID: 30317500 DOI: 10.1007/978-1-4939-8760-3_6] [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] [Indexed: 12/29/2022]
Abstract
Intracellular membrane fusion mediates material and information exchange among different cells or cellular compartments with high accuracy and spatiotemporal resolution. Fusion is driven by ordered folding and assembly of soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) receptors (SNAREs) and regulated by many other proteins. Understanding regulated SNARE assembly is key to dissecting mechanisms and physiologies of various fusion processes and their associated diseases. Yet, it remains challenging to study regulated SNARE assembly using traditional ensemble-based experimental approaches. Here, we describe our new method to measure the energy and kinetics of neuronal SNARE assembly in the presence of α-SNAP, using a single-molecule manipulation approach based on high-resolution optical tweezers. Detailed experimental protocols and methods of data analysis are shown. This approach can be widely applied to elucidate the effects of regulatory proteins on SNARE assembly and membrane fusion.
Collapse
Affiliation(s)
- Lu Ma
- Beijing National Laboratory for Condensed Matter Physics and CAS Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China
| | - Junyi Jiao
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA.,Integrated Graduate Program in Physical and Engineering Biology, New Haven, CT, USA
| | - Yongli Zhang
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA.
| |
Collapse
|
25
|
Karatekin E. Toward a unified picture of the exocytotic fusion pore. FEBS Lett 2018; 592:3563-3585. [PMID: 30317539 PMCID: PMC6353554 DOI: 10.1002/1873-3468.13270] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Revised: 09/30/2018] [Accepted: 10/10/2018] [Indexed: 11/07/2022]
Abstract
Neurotransmitter and hormone release involve calcium-triggered fusion of a cargo-loaded vesicle with the plasma membrane. The initial connection between the fusing membranes, called the fusion pore, can evolve in various ways, including rapid dilation to allow full cargo release, slow expansion, repeated opening-closing and resealing. Pore dynamics determine the kinetics of cargo release and the mode of vesicle recycling, but how these processes are controlled is poorly understood. Previous reconstitutions could not monitor single pores, limiting mechanistic insight they could provide. Recently developed nanodisc-based fusion assays allow reconstitution and monitoring of single pores with unprecedented detail and hold great promise for future discoveries. They recapitulate various aspects of exocytotic fusion pores, but comparison is difficult because different approaches suggested very different exocytotic fusion pore properties, even for the same cell type. In this Review, I discuss how most of the data can be reconciled, by recognizing how different methods probe different aspects of the same fusion process. The resulting picture is that fusion pores have broadly distributed properties arising from stochastic processes which can be modulated by physical constraints imposed by proteins, lipids and membranes.
Collapse
Affiliation(s)
- Erdem Karatekin
- Department of Cellular and Molecular Physiology, Yale University, New Haven, CT, USA
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, USA
- Nanobiology Institute, Yale University, West Haven, CT, USA
- Centre National de la Recherche Scientifique (CNRS), Paris, France
| |
Collapse
|
26
|
Kiessling V, Kreutzberger AJB, Liang B, Nyenhuis SB, Seelheim P, Castle JD, Cafiso DS, Tamm LK. A molecular mechanism for calcium-mediated synaptotagmin-triggered exocytosis. Nat Struct Mol Biol 2018; 25:911-917. [PMID: 30291360 PMCID: PMC6176490 DOI: 10.1038/s41594-018-0130-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2018] [Accepted: 07/31/2018] [Indexed: 12/01/2022]
Abstract
The regulated exocytotic release of neurotransmitter and hormones is accomplished by a complex protein machinery consisting in its core of SNARE proteins and the calcium sensor synaptotagmin-1. We propose a mechanism where the lipid membrane is intimately involved in coupling calcium sensing to release. We demonstrate that fusion of dense core vesicles, derived from rat PC12 cells is strongly linked to the angle between the cytoplasmic domain of the SNARE complex and the plane of the target membrane. We propose that, as this tilt angle increases, force is exerted on the SNARE transmembrane domains to drive the merger of the two bilayers. The tilt angle dramatically increases upon calcium-mediated binding of synaptotagmin to membranes, strongly depends on the surface electrostatics of the membrane, and is strictly coupled to lipid order of the target membrane.
Collapse
Affiliation(s)
- Volker Kiessling
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA, USA. .,Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA.
| | - Alex J B Kreutzberger
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA, USA.,Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| | - Binyong Liang
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA, USA.,Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| | - Sarah B Nyenhuis
- Department of Chemistry, University of Virginia, Charlottesville, VA, USA
| | - Patrick Seelheim
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA, USA.,Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| | - J David Castle
- Department of Cell Biology, University of Virginia, Charlottesville, VA, USA
| | - David S Cafiso
- Department of Chemistry, University of Virginia, Charlottesville, VA, USA
| | - Lukas K Tamm
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA, USA.,Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| |
Collapse
|
27
|
Snead D, Eliezer D. Spectroscopic Characterization of Structure-Function Relationships in the Intrinsically Disordered Protein Complexin. Methods Enzymol 2018; 611:227-286. [PMID: 30471689 DOI: 10.1016/bs.mie.2018.08.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Complexins play a critical role in the regulation of neurotransmission by regulating SNARE-mediated exocytosis of synaptic vesicles. Complexins can exert either a facilitatory or an inhibitory effect on neurotransmitter release, depending on the context, and different complexin domains contribute differently to these opposing roles. Structural characterization of the central helix domain of complexin bound to the assembled SNARE bundle provided key insights into the functional mechanism of this domain of complexin, which is critical for both complexin activities, but many questions remain, particularly regarding the roles and mechanisms of other complexin domains. Recent progress has clarified the structural properties of these additional domains, and has led to various proposals regarding how they contribute to complexin function. This chapter describes spectroscopic approaches used in our laboratory and others, primarily involving circular dichroism and solution-state NMR spectroscopy, to characterize structure within complexins when isolated or when bound to interaction partners. The ability to characterize complexin structure enables structure/function studies employing in vitro or in vivo assays of complexin function. More generally, these types of approaches can be used to study the binding of other intrinsically disordered proteins or protein regions to membrane surfaces or for that matter to other large physiological binding partners.
Collapse
Affiliation(s)
- David Snead
- Department of Biochemistry, Weill Cornell Medicine, New York, NY, United States
| | - David Eliezer
- Department of Biochemistry, Weill Cornell Medicine, New York, NY, United States.
| |
Collapse
|
28
|
Park Y, Ryu JK. Models of synaptotagmin-1 to trigger Ca 2+ -dependent vesicle fusion. FEBS Lett 2018; 592:3480-3492. [PMID: 30004579 DOI: 10.1002/1873-3468.13193] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Revised: 07/02/2018] [Accepted: 07/06/2018] [Indexed: 11/08/2022]
Abstract
Vesicles in neurons and neuroendocrine cells store neurotransmitters and peptide hormones, which are released by vesicle fusion in response to Ca2+ -evoking stimuli. Synaptotagmin-1 (Syt1), a Ca2+ sensor, mediates ultrafast exocytosis in neurons and neuroendocrine cells. After vesicle docking, Syt1 has two main groups of binding partners: anionic phospholipids and the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) complex. The molecular mechanisms by which Syt1 triggers vesicle fusion remain controversial. This Review introduces and summarizes six molecular models of Syt1: (a) Syt1 triggers SNARE unclamping by displacing complexin, (b) Syt1 clamps SNARE zippering, (c) Syt1 causes membrane curvature, (d) membrane bridging by Syt1, (e) Syt1 is a vesicle-plasma membrane distance regulator, and (f) Syt1 undergoes circular oligomerization. We discuss important conditions to test Syt1 activity in vitro and attempt to illustrate the possible roles of Syt1.
Collapse
Affiliation(s)
- Yongsoo Park
- Department of Molecular Biology and Genetics, Koç University, Istanbul, Turkey
| | - Je-Kyung Ryu
- Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, The Netherlands
| |
Collapse
|
29
|
Makke M, Mantero Martinez M, Gaya S, Schwarz Y, Frisch W, Silva-Bermudez L, Jung M, Mohrmann R, Dhara M, Bruns D. A mechanism for exocytotic arrest by the Complexin C-terminus. eLife 2018; 7:38981. [PMID: 30044227 PMCID: PMC6075865 DOI: 10.7554/elife.38981] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Accepted: 07/24/2018] [Indexed: 12/29/2022] Open
Abstract
ComplexinII (CpxII) inhibits non-synchronized vesicle fusion, but the underlying mechanisms have remained unclear. Here, we provide evidence that the far C-terminal domain (CTD) of CpxII interferes with SNARE assembly, thereby arresting tonic exocytosis. Acute infusion of a CTD-derived peptide into mouse chromaffin cells enhances synchronous release by diminishing premature vesicle fusion like full-length CpxII, indicating a direct, inhibitory function of the CTD that sets the magnitude of the primed vesicle pool. We describe a high degree of structural similarity between the CpxII CTD and the SNAP25-SN1 domain (C-terminal half) and show that the CTD peptide lowers the rate of SDS-resistant SNARE complex formation in vitro. Moreover, corresponding CpxII:SNAP25 chimeras do restore complexin's function and even 'superclamp' tonic secretion. Collectively, these results support a so far unrecognized clamping mechanism wherein the CpxII C-terminus hinders spontaneous SNARE complex assembly, enabling the build-up of a release-ready pool of vesicles for synchronized Ca2+-triggered exocytosis.
Collapse
Affiliation(s)
- Mazen Makke
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, University of Saarland, Homburg, Germany
| | - Maria Mantero Martinez
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, University of Saarland, Homburg, Germany
| | - Surya Gaya
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, University of Saarland, Homburg, Germany
| | - Yvonne Schwarz
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, University of Saarland, Homburg, Germany
| | - Walentina Frisch
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, University of Saarland, Homburg, Germany
| | - Lina Silva-Bermudez
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, University of Saarland, Homburg, Germany
| | - Martin Jung
- Institute for Medical Biochemistry and Molecular Biology, University of Saarland, Homburg, Germany
| | - Ralf Mohrmann
- Institute for Physiology, Otto-von-Guericke University, Magdeburg, Germany
| | - Madhurima Dhara
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, University of Saarland, Homburg, Germany
| | - Dieter Bruns
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, University of Saarland, Homburg, Germany
| |
Collapse
|
30
|
Rizo J. Mechanism of neurotransmitter release coming into focus. Protein Sci 2018; 27:1364-1391. [PMID: 29893445 DOI: 10.1002/pro.3445] [Citation(s) in RCA: 134] [Impact Index Per Article: 22.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2018] [Accepted: 05/10/2018] [Indexed: 12/11/2022]
Abstract
Research for three decades and major recent advances have provided crucial insights into how neurotransmitters are released by Ca2+ -triggered synaptic vesicle exocytosis, leading to reconstitution of basic steps that underlie Ca2+ -dependent membrane fusion and yielding a model that assigns defined functions for central components of the release machinery. The soluble N-ethyl maleimide sensitive factor attachment protein receptors (SNAREs) syntaxin-1, SNAP-25, and synaptobrevin-2 form a tight SNARE complex that brings the vesicle and plasma membranes together and is key for membrane fusion. N-ethyl maleimide sensitive factor (NSF) and soluble NSF attachment proteins (SNAPs) disassemble the SNARE complex to recycle the SNAREs for another round of fusion. Munc18-1 and Munc13-1 orchestrate SNARE complex formation in an NSF-SNAP-resistant manner by a mechanism whereby Munc18-1 binds to synaptobrevin and to a self-inhibited "closed" conformation of syntaxin-1, thus forming a template to assemble the SNARE complex, and Munc13-1 facilitates assembly by bridging the vesicle and plasma membranes and catalyzing opening of syntaxin-1. Synaptotagmin-1 functions as the major Ca2+ sensor that triggers release by binding to membrane phospholipids and to the SNAREs, in a tight interplay with complexins that accelerates membrane fusion. Many of these proteins act as both inhibitors and activators of exocytosis, which is critical for the exquisite regulation of neurotransmitter release. It is still unclear how the actions of these various proteins and multiple other components that control release are integrated and, in particular, how they induce membrane fusion, but it can be expected that these fundamental questions can be answered in the near future, building on the extensive knowledge already available.
Collapse
Affiliation(s)
- Josep Rizo
- Departments of Biophysics, Biochemistry and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, 75390
| |
Collapse
|
31
|
A convenient protocol for generating giant unilamellar vesicles containing SNARE proteins using electroformation. Sci Rep 2018; 8:9422. [PMID: 29930377 PMCID: PMC6013450 DOI: 10.1038/s41598-018-27456-4] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2018] [Accepted: 05/29/2018] [Indexed: 01/05/2023] Open
Abstract
Reconstitution of membrane proteins in artificial membranes is an essential prerequisite for functional studies that depend on the context of an intact membrane. While straight-forward protocols for reconstituting proteins in small unilamellar vesicles were developed many years ago, it is much more difficult to prepare large membranes containing membrane proteins at biologically relevant concentrations. Giant unilamellar vesicles (GUVs) represent a model system that is characterised by low curvature, controllable tension, and large surface that can be easily visualised with microscopy, but protein insertion is notoriously difficult. Here we describe a convenient method for efficient generation of GUVs containing functionally active SNARE proteins that govern exocytosis of synaptic vesicles. Preparation of proteo-GUVs requires a simple, in-house-built device, standard and inexpensive electronic equipment, and employs a straight-forward protocol that largely avoids damage of the proteins. The procedure allows upscaling and multiplexing, thus providing a platform for establishing and optimizing preparation of GUVs containing membrane proteins for a diverse array of applications.
Collapse
|
32
|
Singh P, Hui CY. Hydrodynamics govern the pre-fusion docking time of synaptic vesicles. J R Soc Interface 2018; 15:rsif.2017.0818. [PMID: 29386403 DOI: 10.1098/rsif.2017.0818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Accepted: 01/09/2018] [Indexed: 11/12/2022] Open
Abstract
Synaptic vesicle fusion is a crucial step in the neurotransmission process. Neurotransmitter-filled vesicles are pre-docked at the synapse by the mediation of ribbon structures and SNARE proteins at the ribbon synapses. An electrical impulse triggers the fusion process of pre-docked vesicles, leading to the formation of a fusion pore and subsequently resulting in the release of neurotransmitter into the synaptic cleft. In this study, a continuum model of lipid membrane along with lubrication theory is used to determine the traverse time of the synaptic vesicle under the influence of hydrodynamic forces. We find that the traverse time is strongly dependent on how fast the driving force decays or grows with closure of the gap between the vesicle and the plasma membrane. If the correct behaviour is chosen, the traverse time obtained is of the order of a few hundred milliseconds and lies within the experimentally obtained value of approximately 250 ms (Zenisek D, Steyer JA, Almers W. 2000 Nature406, 849-854 (doi:10.1038/35022500)). We hypothesize that there are two different force behaviours, which complies with the experimental findings of pre-fusion docking of synaptic vesicles at the ribbon synapses. The common theme in the proposed force models is that the driving force has to very rapidly increase or decrease with the amount of clamping.
Collapse
Affiliation(s)
- Pankaj Singh
- Department of Theoretical and Applied Mechanics, Cornell University, Ithaca, NY 14853, USA
| | - Chung-Yuen Hui
- Department of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA
| |
Collapse
|
33
|
Meijer M, Dörr B, Lammertse HC, Blithikioti C, van Weering JR, Toonen RF, Söllner TH, Verhage M. Tyrosine phosphorylation of Munc18-1 inhibits synaptic transmission by preventing SNARE assembly. EMBO J 2017; 37:300-320. [PMID: 29150433 PMCID: PMC5770875 DOI: 10.15252/embj.201796484] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2017] [Revised: 10/12/2017] [Accepted: 10/16/2017] [Indexed: 11/17/2022] Open
Abstract
Tyrosine kinases are important regulators of synaptic strength. Here, we describe a key component of the synaptic vesicle release machinery, Munc18‐1, as a phosphorylation target for neuronal Src family kinases (SFKs). Phosphomimetic Y473D mutation of a SFK phosphorylation site previously identified by brain phospho‐proteomics abolished the stimulatory effect of Munc18‐1 on SNARE complex formation (“SNARE‐templating”) and membrane fusion in vitro. Furthermore, priming but not docking of synaptic vesicles was disrupted in hippocampal munc18‐1‐null neurons expressing Munc18‐1Y473D. Synaptic transmission was temporarily restored by high‐frequency stimulation, as well as by a Munc18‐1 mutation that results in helix 12 extension, a critical conformational step in vesicle priming. On the other hand, expression of non‐phosphorylatable Munc18‐1 supported normal synaptic transmission. We propose that SFK‐dependent Munc18‐1 phosphorylation may constitute a potent, previously unknown mechanism to shut down synaptic transmission, via direct occlusion of a Synaptobrevin/VAMP2 binding groove and subsequent hindrance of conformational changes in domain 3a responsible for vesicle priming. This would strongly interfere with the essential post‐docking SNARE‐templating role of Munc18‐1, resulting in a largely abolished pool of releasable synaptic vesicles.
Collapse
Affiliation(s)
- Marieke Meijer
- Department of Clinical Genetics, Center for Neurogenomics and Cognitive Research (CNCR), Neuroscience Campus Amsterdam (NCA) VU University Medical Center, Amsterdam, The Netherlands
| | - Bernhard Dörr
- Heidelberg University Biochemistry Center (BZH), Heidelberg, Germany
| | - Hanna Ca Lammertse
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research (CNCR), Neuroscience Campus Amsterdam (NCA) VU University Amsterdam, Amsterdam, The Netherlands
| | - Chrysanthi Blithikioti
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research (CNCR), Neuroscience Campus Amsterdam (NCA) VU University Amsterdam, Amsterdam, The Netherlands
| | - Jan Rt van Weering
- Department of Clinical Genetics, Center for Neurogenomics and Cognitive Research (CNCR), Neuroscience Campus Amsterdam (NCA) VU University Medical Center, Amsterdam, The Netherlands
| | - Ruud Fg Toonen
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research (CNCR), Neuroscience Campus Amsterdam (NCA) VU University Amsterdam, Amsterdam, The Netherlands
| | - Thomas H Söllner
- Heidelberg University Biochemistry Center (BZH), Heidelberg, Germany
| | - Matthijs Verhage
- Department of Clinical Genetics, Center for Neurogenomics and Cognitive Research (CNCR), Neuroscience Campus Amsterdam (NCA) VU University Medical Center, Amsterdam, The Netherlands .,Department of Functional Genomics, Center for Neurogenomics and Cognitive Research (CNCR), Neuroscience Campus Amsterdam (NCA) VU University Amsterdam, Amsterdam, The Netherlands
| |
Collapse
|
34
|
Dhara M, Mohrmann R, Bruns D. v-SNARE function in chromaffin cells. Pflugers Arch 2017; 470:169-180. [PMID: 28887593 PMCID: PMC5748422 DOI: 10.1007/s00424-017-2066-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Revised: 08/28/2017] [Accepted: 08/29/2017] [Indexed: 01/04/2023]
Abstract
Vesicle fusion is elementary for intracellular trafficking and release of signal molecules, thus providing the basis for diverse forms of intercellular communication like hormonal regulation or synaptic transmission. A detailed characterization of the mechanisms underlying exocytosis is key to understand how the nervous system integrates information and generates appropriate responses to stimuli. The machinery for vesicular release employs common molecular players in different model systems including neuronal and neuroendocrine cells, in particular members of the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) protein family, Sec1/Munc18-like proteins, and other accessory factors. To achieve temporal precision and speed, excitable cells utilize specialized regulatory proteins like synaptotagmin and complexin, whose interplay putatively synchronizes vesicle fusion and enhances stimulus-secretion coupling. In this review, we aim to highlight recent progress and emerging views on the molecular mechanisms, by which constitutively forming SNAREpins are organized in functional, tightly regulated units for synchronized release. Specifically, we will focus on the role of vesicle associated membrane proteins, also referred to as vesicular SNAREs, in fusion and rapid cargo discharge. We will further discuss the functions of SNARE regulators during exocytosis and focus on chromaffin cell as a model system of choice that allows for detailed structure-function analyses and direct measurements of vesicle fusion under precise control of intracellular [Ca]i.
Collapse
Affiliation(s)
- Madhurima Dhara
- Molecular Neurophysiology, CIPMM, Medical Faculty, Saarland University, 66421, Homburg/Saar, Germany
| | - Ralf Mohrmann
- Zentrum für Human- und Molekularbiologie, Saarland University, 66421, Homburg/Saar, Germany
| | - Dieter Bruns
- Molecular Neurophysiology, CIPMM, Medical Faculty, Saarland University, 66421, Homburg/Saar, Germany.
| |
Collapse
|
35
|
Interactions Between SNAP-25 and Synaptotagmin-1 Are Involved in Vesicle Priming, Clamping Spontaneous and Stimulating Evoked Neurotransmission. J Neurosci 2017; 36:11865-11880. [PMID: 27881774 DOI: 10.1523/jneurosci.1011-16.2016] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2016] [Revised: 09/29/2016] [Accepted: 09/29/2016] [Indexed: 01/20/2023] Open
Abstract
Whether interactions between synaptotagmin-1 (syt-1) and the soluble NSF attachment protein receptors (SNAREs) are required during neurotransmission is debated. We examined five SNAP-25 mutations designed to interfere with syt-1 interactions. One mutation, D51/E52/E55A, targeted negative charges within region II of the primary interface (Zhou et al., 2015); two mutations targeted region I (D166A and D166/E170A) and one mutation targeted both (D51/E52/E55/D166A). The final mutation (D186/D193A) targeted C-terminal residues not expected to interact with syt-1. An in vitro assay showed that the region I, region II, and region I+II (D51/E52/E55/D166A) mutants markedly reduced the attachment between syt-1 and t-SNARE-carrying vesicles in the absence of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2]. In the presence of PI(4,5)P2, vesicle attachment was unaffected by mutation. When expressed in Snap-25-null mouse autaptic neurons, region I mutations reduced the size of the readily releasable pool of vesicles, whereas the region II mutation reduced vesicular release probability. Combining both in the D51/E52/E55/D166A mutation abrogated evoked release. These data point to a division of labor between region I (vesicle priming) and region II (evoked release). Spontaneous release was disinhibited by region I mutations and found to correlate with defective complexin (Cpx) clamping in an in vitro fusion assay, pointing to an interdependent role of synaptotagmin and Cpx in release clamping. Mutation in region II (D51/E52/E55A) also unclamped release, but this effect could be overcome by synaptotagmin overexpression, arguing against an obligatory role in clamping. We conclude that three synaptic release functions of syt-1, vesicle priming, spontaneous release clamping, and evoked release triggering, depend on direct SNARE complex interaction. SIGNIFICANCE STATEMENT The function of synaptotagmin-1 (syt-1):soluble NSF attachment protein receptor (SNARE) interactions during neurotransmission remains unclear. We mutated SNAP-25 within the recently identified region I and region II of the primary synaptotagmin:SNARE interface. Using in vitro assays and rescue experiments in autaptic neurons, we show that interactions within region II of the primary interface are necessary for synchronized calcium-triggered release, whereas region I is involved in vesicle priming. Spontaneous release was disinhibited by region I mutation and found to correlate with defective complexin (Cpx) clamping in vitro, pointing to an interdependent role of synaptotagmin and Cpx in release clamping. Therefore, vesicle priming, clamping spontaneous release, and eliciting evoked release are three different functions of syt-1 that involve different interaction modes with the SNARE complex.
Collapse
|
36
|
Extension of Helix 12 in Munc18-1 Induces Vesicle Priming. J Neurosci 2017; 36:6881-91. [PMID: 27358447 DOI: 10.1523/jneurosci.0007-16.2016] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2016] [Accepted: 05/14/2016] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Munc18-1 is essential for vesicle fusion and participates in the docking of large dense-core vesicles to the plasma membrane. Recent structural data suggest that conformational changes in the 12th helix of the Munc18-1 domain 3a within the Munc18-1:syntaxin complex result in an additional interaction with synaptobrevin-2/VAMP2 (vesicle-associated membrane protein 2), leading to SNARE complex formation. To test this hypothesis in living cells, we examined secretion from Munc18-1-null mouse adrenal chromaffin cells expressing Munc18-1 mutants designed to either perturb the extension of helix 12 (Δ324-339), block its interaction with synaptobrevin-2 (L348R), or extend the helix to promote coil-coil interactions with other proteins (P335A). The mutants rescued vesicle docking and syntaxin-1 targeting to the plasma membrane, with the exception of P335A that only supported partial syntaxin-1 targeting. Disruptive mutations (L348R or Δ324-339) lowered the secretory amplitude by decreasing vesicle priming, whereas P335A markedly increased priming and secretory amplitude. The mutants displayed unchanged kinetics and Ca(2+) dependence of fusion, indicating that the mutations specifically affect the vesicle priming step. Mutation of a nearby tyrosine (Y337A), which interacts with closed syntaxin-1, mildly increased secretory amplitude. This correlated with results from an in vitro fusion assay probing the functions of Munc18-1, indicating an easier transition to the extended state in the mutant. Our findings support the notion that a conformational transition within the Munc18-1 domain 3a helix 12 leads to opening of a closed Munc18-1:syntaxin complex, followed by productive SNARE complex assembly and vesicle priming. SIGNIFICANCE STATEMENT The essential postdocking role of Munc18-1 in vesicular exocytosis has remained elusive, but recent data led to the hypothesis that the extension of helix 12 in Munc18 within domain 3a leads to synaptobrevin-2/VAMP2 interaction and SNARE complex formation. Using both lack-of-function and gain-of-function mutants, we here report that the conformation of helix 12 predicts vesicle priming and secretory amplitude in living chromaffin cells. The effects of mutants on secretion could not be explained by differences in syntaxin-1 chaperoning/localization or vesicle docking, and the fusion kinetics and calcium dependence were unchanged, indicating that the effect of helix 12 extension is specific for the vesicle-priming step. We conclude that a conformational change within helix 12 is responsible for the essential postdocking role of Munc18-1 in neurosecretion.
Collapse
|
37
|
Zdanowicz R, Kreutzberger A, Liang B, Kiessling V, Tamm LK, Cafiso DS. Complexin Binding to Membranes and Acceptor t-SNAREs Explains Its Clamping Effect on Fusion. Biophys J 2017; 113:1235-1250. [PMID: 28456331 DOI: 10.1016/j.bpj.2017.04.002] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2017] [Revised: 03/31/2017] [Accepted: 04/04/2017] [Indexed: 02/07/2023] Open
Abstract
Complexin-1 is a SNARE effector protein that decreases spontaneous neurotransmitter release and enhances evoked release. Complexin binds to the fully assembled four-helical neuronal SNARE core complex as revealed in competing molecular models derived from x-ray crystallography. Presently, it is unclear how complexin binding to the postfusion complex accounts for its effects upon spontaneous and evoked release in vivo. Using a combination of spectroscopic and imaging methods, we characterize in molecular detail how complexin binds to the 1:1 plasma membrane t-SNARE complex of syntaxin-1a and SNAP-25 while simultaneously binding the lipid bilayer at both its N- and C-terminal ends. These interactions are cooperative, and binding to the prefusion acceptor t-SNARE complex is stronger than to the postfusion core complex. This complexin interaction reduces the affinity of synaptobrevin-2 for the 1:1 complex, thereby retarding SNARE assembly and vesicle docking in vitro. The results provide the basis for molecular models that account for the observed clamping effect of complexin beginning with the acceptor t-SNARE complex and the subsequent activation of the clamped complex by Ca2+ and synaptotagmin.
Collapse
Affiliation(s)
- Rafal Zdanowicz
- Department of Chemistry, University of Virginia, Charlottesville, Virginia; Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, Virginia
| | - Alex Kreutzberger
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, Virginia; Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia
| | - Binyong Liang
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, Virginia; Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia
| | - Volker Kiessling
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, Virginia; Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia
| | - Lukas K Tamm
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, Virginia; Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia.
| | - David S Cafiso
- Department of Chemistry, University of Virginia, Charlottesville, Virginia; Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, Virginia.
| |
Collapse
|
38
|
Witkowska A, Jahn R. Rapid SNARE-Mediated Fusion of Liposomes and Chromaffin Granules with Giant Unilamellar Vesicles. Biophys J 2017; 113:1251-1259. [PMID: 28400045 PMCID: PMC5607038 DOI: 10.1016/j.bpj.2017.03.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2016] [Revised: 03/12/2017] [Accepted: 03/13/2017] [Indexed: 11/03/2022] Open
Abstract
Soluble N-ethylmaleimide-sensitive factor activating protein receptor (SNARE) proteins are the main catalysts for membrane fusion in the secretory pathway of eukaryotic cells. In vitro, SNAREs are sufficient to mediate effective fusion of both native and artificial membranes. Here we have established, to our knowledge, a new platform for monitoring SNARE-mediated docking and fusion between giant unilamellar vesicles (GUVs) and smaller liposomes or purified secretory granules with high temporal and spatial resolution. Analysis of fusion is restricted to the free-standing part of the GUV-membrane exhibiting low curvature and a lack of surface contact, thus avoiding adhesion-mediated interference with the fusion reaction as in fusion with supported bilayers or surface-immobilized small vesicles. Our results show that liposomes and chromaffin granules fuse with GUVs containing activated SNAREs with only few milliseconds delay between docking and fusion. We conclude that after initial contact in trans, SNAREs alone can complete fusion at a rate close to fast neuronal exocytosis.
Collapse
Affiliation(s)
- Agata Witkowska
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany; International Max Planck Research School for Molecular Biology at the University of Göttingen, Göttingen, Germany
| | - Reinhard Jahn
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.
| |
Collapse
|
39
|
Heo P, Park JB, Shin YK, Kweon DH. Visualization of SNARE-Mediated Hemifusion between Giant Unilamellar Vesicles Arrested by Myricetin. Front Mol Neurosci 2017; 10:93. [PMID: 28408867 PMCID: PMC5374201 DOI: 10.3389/fnmol.2017.00093] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2016] [Accepted: 03/20/2017] [Indexed: 11/13/2022] Open
Abstract
Neurotransmitters are released within a millisecond after Ca2+ arrives at an active zone. However, the vesicle fusion pathway underlying this synchronous release is yet to be understood. At the center of controversy is whether hemifusion, in which outer leaflets are merged while inner leaflets are still separated, is an on-pathway or off-pathway product of Ca2+-triggered exocytosis. Using the single vesicle fusion assay, we recently demonstrated that hemifusion is an on-pathway intermediate that immediately proceeds to full fusion upon Ca2+ triggering. It has been shown that the flavonoid myricetin arrests soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein receptor (SNARE)-mediated vesicle fusion at hemifusion, but that the hemifused vesicles spontaneously convert to full fusion when the myricetin clamp is removed by the enzyme laccase. In the present study, we visualized SNARE-mediated hemifusion between two SNARE-reconstituted giant unilamellar vesicles (GUVs) arrested by myricetin. The large size of the GUVs enabled us to directly image the hemifusion between them. When two merging GUVs were labeled with different fluorescent dyes, GUV pairs showed asymmetric fluorescence intensities depending on the position on the GUV pair consistent with what is expected for hemifusion. The flow of lipids from one vesicle to the other was revealed with fluorescence recovery after photobleaching (FRAP), indicating that the two membranes had hemifused. These results support the hypothesis that hemifusion may be the molecular status that primes Ca2+-triggered millisecond exocytosis. This study represents the first imaging of SNARE-driven hemifusion between GUVs.
Collapse
Affiliation(s)
- Paul Heo
- Department of Genetic Engineering, College of Biotechnology and Bioengineering, Sungkyunkwan UniversitySuwon, South Korea
| | - Joon-Bum Park
- Department of Genetic Engineering, College of Biotechnology and Bioengineering, Sungkyunkwan UniversitySuwon, South Korea
| | - Yeon-Kyun Shin
- Department of Biochemistry, Biophysics and Molecular Biology, Iowa State UniversityAmes, IA, USA
| | - Dae-Hyuk Kweon
- Department of Genetic Engineering, College of Biotechnology and Bioengineering, Sungkyunkwan UniversitySuwon, South Korea
| |
Collapse
|
40
|
François-Martin C, Pincet F. Actual fusion efficiency in the lipid mixing assay - Comparison between nanodiscs and liposomes. Sci Rep 2017; 7:43860. [PMID: 28266607 PMCID: PMC5339690 DOI: 10.1038/srep43860] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Accepted: 01/31/2017] [Indexed: 01/19/2023] Open
Abstract
Lipid exchange occurs between membranes during fusion or active lipid transfer. These processes are necessary in vivo for the homeostasis of the cell at the level of the membranes, the organelles and the cell itself. They are also used by the cell to interact with the surrounding medium. Several assays have been developed to characterize in vitro these processes on model systems. The most common one, relying on fluorescence dequenching, measures lipid mixing between small membranes such as liposomes or nanodiscs in bulk. Usually, relative comparisons of the rate of lipid exchange are made between measurements performed in parallel. Here, we establish a quantitative standardization of this assay to avoid any bias resulting from the temperatures, the chosen fluorescent lipid fractions and from the various detergents used to normalize the measurements. We used this standardization to quantitatively compare the efficiency of SNARE-induced fusion in liposome-liposome and liposome-nanodisc configurations having similar collision frequency. We found that the initial yield of fusion is comparable in both cases, 1 per 2-3 million collisions in spite of a much larger dequenching signal with nanodiscs. Also, the long-term actual fusion rate is slightly lower with nanodiscs than in the liposome-liposome assay.
Collapse
Affiliation(s)
- Claire François-Martin
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, Paris Sciences et Lettres Research University, 75005, Paris, France.,Laboratoire de Physique Statistique, Université Paris Diderot Sorbonne Paris Cité, 75005, Paris, France.,Laboratoire de Physique Statistique, Sorbonne Universités, Université Pierre et Marie Curie, Univ Paris 06, CNRS, 75005, Paris, France.,Laboratoire de Physique Statistique, Ecole Normale Supérieure, Paris Sciences et Lettres Research University, 75005, Paris, France
| | - Frédéric Pincet
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, Paris Sciences et Lettres Research University, 75005, Paris, France.,Laboratoire de Physique Statistique, Université Paris Diderot Sorbonne Paris Cité, 75005, Paris, France.,Laboratoire de Physique Statistique, Sorbonne Universités, Université Pierre et Marie Curie, Univ Paris 06, CNRS, 75005, Paris, France.,Laboratoire de Physique Statistique, Ecole Normale Supérieure, Paris Sciences et Lettres Research University, 75005, Paris, France
| |
Collapse
|
41
|
Han J, Pluhackova K, Böckmann RA. The Multifaceted Role of SNARE Proteins in Membrane Fusion. Front Physiol 2017; 8:5. [PMID: 28163686 PMCID: PMC5247469 DOI: 10.3389/fphys.2017.00005] [Citation(s) in RCA: 178] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Accepted: 01/04/2017] [Indexed: 12/28/2022] Open
Abstract
Membrane fusion is a key process in all living organisms that contributes to a variety of biological processes including viral infection, cell fertilization, as well as intracellular transport, and neurotransmitter release. In particular, the various membrane-enclosed compartments in eukaryotic cells need to exchange their contents and communicate across membranes. Efficient and controllable fusion of biological membranes is known to be driven by cooperative action of SNARE proteins, which constitute the central components of the eukaryotic fusion machinery responsible for fusion of synaptic vesicles with the plasma membrane. During exocytosis, vesicle-associated v-SNARE (synaptobrevin) and target cell-associated t-SNAREs (syntaxin and SNAP-25) assemble into a core trans-SNARE complex. This complex plays a versatile role at various stages of exocytosis ranging from the priming to fusion pore formation and expansion, finally resulting in the release or exchange of the vesicle content. This review summarizes current knowledge on the intricate molecular mechanisms underlying exocytosis triggered and catalyzed by SNARE proteins. Particular attention is given to the function of the peptidic SNARE membrane anchors and the role of SNARE-lipid interactions in fusion. Moreover, the regulatory mechanisms by synaptic auxiliary proteins in SNARE-driven membrane fusion are briefly outlined.
Collapse
Affiliation(s)
- Jing Han
- Department of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Xi'an Jiaotong University Health Science CenterXi'an, China; Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-NürnbergErlangen, Germany
| | - Kristyna Pluhackova
- Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg Erlangen, Germany
| | - Rainer A Böckmann
- Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg Erlangen, Germany
| |
Collapse
|
42
|
Lürick A, Gao J, Kuhlee A, Yavavli E, Langemeyer L, Perz A, Raunser S, Ungermann C. Multivalent Rab interactions determine tether-mediated membrane fusion. Mol Biol Cell 2016; 28:322-332. [PMID: 27852901 PMCID: PMC5231900 DOI: 10.1091/mbc.e16-11-0764] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Accepted: 11/10/2016] [Indexed: 12/22/2022] Open
Abstract
Membrane fusion at endomembranes requires cross-talk between Rab GTPases and tethers to drive SNARE-mediated lipid bilayer mixing. Several tethers have multiple Rab-binding sites with largely untested function. Here we dissected the lysosomal HOPS complex as a tethering complex with just two binding sites for the Rab7-like Ypt7 protein to determine their relevance for fusion. Using tethering and fusion assays combined with HOPS mutants, we show that HOPS-dependent fusion requires both Rab-binding sites, with Vps39 being the stronger Ypt7 interactor than Vps41. The intrinsic amphipathic lipid packaging sensor (ALPS) motif within HOPS Vps41, a target of the vacuolar kinase Yck3, is dispensable for tethering and fusion but can affect tethering if phosphorylated. In combination, our data demonstrate that a multivalent tethering complex uses its two Rab bindings to determine the place of SNARE assembly and thus fusion at endomembranes.
Collapse
Affiliation(s)
- Anna Lürick
- Biochemistry Section, Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany
| | - Jieqiong Gao
- Biochemistry Section, Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany
| | - Anne Kuhlee
- Department of Physical Biochemistry, Max-Planck Institute of Molecular Physiology; 44227 Dortmund, Germany
| | - Erdal Yavavli
- Biochemistry Section, Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany
| | - Lars Langemeyer
- Biochemistry Section, Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany
| | - Angela Perz
- Biochemistry Section, Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany
| | - Stefan Raunser
- Department of Physical Biochemistry, Max-Planck Institute of Molecular Physiology; 44227 Dortmund, Germany
| | - Christian Ungermann
- Biochemistry Section, Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany
| |
Collapse
|
43
|
C-terminal domain of mammalian complexin-1 localizes to highly curved membranes. Proc Natl Acad Sci U S A 2016; 113:E7590-E7599. [PMID: 27821736 DOI: 10.1073/pnas.1609917113] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In presynaptic nerve terminals, complexin regulates spontaneous "mini" neurotransmitter release and activates Ca2+-triggered synchronized neurotransmitter release. We studied the role of the C-terminal domain of mammalian complexin in these processes using single-particle optical imaging and electrophysiology. The C-terminal domain is important for regulating spontaneous release in neuronal cultures and suppressing Ca2+-independent fusion in vitro, but it is not essential for evoked release in neuronal cultures and in vitro. This domain interacts with membranes in a curvature-dependent fashion similar to a previous study with worm complexin [Snead D, Wragg RT, Dittman JS, Eliezer D (2014) Membrane curvature sensing by the C-terminal domain of complexin. Nat Commun 5:4955]. The curvature-sensing value of the C-terminal domain is comparable to that of α-synuclein. Upon replacement of the C-terminal domain with membrane-localizing elements, preferential localization to the synaptic vesicle membrane, but not to the plasma membrane, results in suppression of spontaneous release in neurons. Membrane localization had no measurable effect on evoked postsynaptic currents of AMPA-type glutamate receptors, but mislocalization to the plasma membrane increases both the variability and the mean of the synchronous decay time constant of NMDA-type glutamate receptor evoked postsynaptic currents.
Collapse
|
44
|
N-terminal domain of complexin independently activates calcium-triggered fusion. Proc Natl Acad Sci U S A 2016; 113:E4698-707. [PMID: 27444020 DOI: 10.1073/pnas.1604348113] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Complexin activates Ca(2+)-triggered neurotransmitter release and regulates spontaneous release in the presynaptic terminal by cooperating with the neuronal soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and the Ca(2+)-sensor synaptotagmin. The N-terminal domain of complexin is important for activation, but its molecular mechanism is still poorly understood. Here, we observed that a split pair of N-terminal and central domain fragments of complexin is sufficient to activate Ca(2+)-triggered release using a reconstituted single-vesicle fusion assay, suggesting that the N-terminal domain acts as an independent module within the synaptic fusion machinery. The N-terminal domain can also interact independently with membranes, which is enhanced by a cooperative interaction with the neuronal SNARE complex. We show by mutagenesis that membrane binding of the N-terminal domain is essential for activation of Ca(2+)-triggered fusion. Consistent with the membrane-binding property, the N-terminal domain can be substituted by the influenza virus hemagglutinin fusion peptide, and this chimera also activates Ca(2+)-triggered fusion. Membrane binding of the N-terminal domain of complexin therefore cooperates with the other fusogenic elements of the synaptic fusion machinery during Ca(2+)-triggered release.
Collapse
|
45
|
Trimbuch T, Rosenmund C. Should I stop or should I go? The role of complexin in neurotransmitter release. Nat Rev Neurosci 2016; 17:118-25. [PMID: 26806630 DOI: 10.1038/nrn.2015.16] [Citation(s) in RCA: 107] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
When it comes to fusion with the neuronal cell membrane, does a synaptic vesicle have a choice whether to stop or to go? Recent work suggests that complexin, a tiny protein found within the synaptic terminal, contributes to the mechanism through which this choice is made. How complexin plays this consulting part and which synaptic vesicle proteins it interacts with remain open questions. Indeed, studies in mice and flies have led to the proposal of different models of complexin function. We suggest that understanding the modular nature of complexin will help us to unpick its role in synaptic vesicle release.
Collapse
Affiliation(s)
- Thorsten Trimbuch
- Neuroscience Research Center, Charité Universitätsmedizin Berlin, Chariteplatz 1, 10117 Berlin, Germany
| | - Christian Rosenmund
- Neuroscience Research Center, Charité Universitätsmedizin Berlin, Chariteplatz 1, 10117 Berlin, Germany
| |
Collapse
|
46
|
Xu W, Nathwani B, Lin C, Wang J, Karatekin E, Pincet F, Shih W, Rothman JE. A Programmable DNA Origami Platform to Organize SNAREs for Membrane Fusion. J Am Chem Soc 2016; 138:4439-47. [PMID: 26938705 DOI: 10.1021/jacs.5b13107] [Citation(s) in RCA: 67] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes are the core molecular machinery of membrane fusion, a fundamental process that drives inter- and intracellular communication and trafficking. One of the questions that remains controversial has been whether and how SNAREs cooperate. Here we show the use of self-assembled DNA-nanostructure rings to template uniform-sized small unilamellar vesicles containing predetermined maximal number of externally facing SNAREs to study the membrane-fusion process. We also incorporated lipid-conjugated complementary ssDNA as tethers into vesicle and target membranes, which enabled bypass of the rate-limiting docking step of fusion reactions and allowed direct observation of individual membrane-fusion events at SNARE densities as low as one pair per vesicle. With this platform, we confirmed at the single event level that, after docking of the templated-SUVs to supported lipid bilayers (SBL), one to two pairs of SNAREs are sufficient to drive fast lipid mixing. Modularity and programmability of this platform makes it readily amenable to studying more complicated systems where auxiliary proteins are involved.
Collapse
Affiliation(s)
| | - Bhavik Nathwani
- Wyss Institute for Biologically Inspired Engineering and Biological Chemistry and Molecular Pharmacology, Harvard Medical School, and Department of Cancer Biology, Dana Farber Cancer Institute , Boston, Massachusetts 02115, United States
| | - Chenxiang Lin
- Wyss Institute for Biologically Inspired Engineering and Biological Chemistry and Molecular Pharmacology, Harvard Medical School, and Department of Cancer Biology, Dana Farber Cancer Institute , Boston, Massachusetts 02115, United States
| | | | - Erdem Karatekin
- Laboratoire de Neurophotonique, Université Paris Descartes, Faculté des Sciences Fondamentales et Biomédicales, Centre National de la Recherche Scientifique (CNRS) UMR8250, 45, rue des Saints Pères, 75270 Cedex 06 Paris, France
| | - Frederic Pincet
- Laboratoire de Physique Statistique, Ecole Normale Supérieure de Paris, Université Pierre et Marie Curie, Université Paris Diderot, Centre National de la Recherche Scientifique, UMR 8550, 24 rue Lhomond, 75005 Paris, France
| | - William Shih
- Wyss Institute for Biologically Inspired Engineering and Biological Chemistry and Molecular Pharmacology, Harvard Medical School, and Department of Cancer Biology, Dana Farber Cancer Institute , Boston, Massachusetts 02115, United States
| | | |
Collapse
|
47
|
Cho RW, Buhl LK, Volfson D, Tran A, Li F, Akbergenova Y, Littleton JT. Phosphorylation of Complexin by PKA Regulates Activity-Dependent Spontaneous Neurotransmitter Release and Structural Synaptic Plasticity. Neuron 2016; 88:749-61. [PMID: 26590346 DOI: 10.1016/j.neuron.2015.10.011] [Citation(s) in RCA: 58] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2015] [Revised: 08/20/2015] [Accepted: 09/29/2015] [Indexed: 10/22/2022]
Abstract
Synaptic plasticity is a fundamental feature of the nervous system that allows adaptation to changing behavioral environments. Most studies of synaptic plasticity have examined the regulated trafficking of postsynaptic glutamate receptors that generates alterations in synaptic transmission. Whether and how changes in the presynaptic release machinery contribute to neuronal plasticity is less clear. The SNARE complex mediates neurotransmitter release in response to presynaptic Ca(2+) entry. Here we show that the SNARE fusion clamp Complexin undergoes activity-dependent phosphorylation that alters the basic properties of neurotransmission in Drosophila. Retrograde signaling following stimulation activates PKA-dependent phosphorylation of the Complexin C terminus that selectively and transiently enhances spontaneous release. Enhanced spontaneous release is required for activity-dependent synaptic growth. These data indicate that SNARE-dependent fusion mechanisms can be regulated in an activity-dependent manner and highlight the key role of spontaneous neurotransmitter release as a mediator of functional and structural plasticity.
Collapse
Affiliation(s)
- Richard W Cho
- Department of Biology and Department of Brain and Cognitive Sciences, The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
| | - Lauren K Buhl
- Department of Biology and Department of Brain and Cognitive Sciences, The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Dina Volfson
- Department of Biology and Department of Brain and Cognitive Sciences, The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Adrienne Tran
- Department of Biology and Department of Brain and Cognitive Sciences, The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Feng Li
- Department of Cell Biology, Nanobiology Institute, School of Medicine, Yale University, New Haven, CT 06520, USA
| | - Yulia Akbergenova
- Department of Biology and Department of Brain and Cognitive Sciences, The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - J Troy Littleton
- Department of Biology and Department of Brain and Cognitive Sciences, The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| |
Collapse
|
48
|
Fortoul N, Singh P, Hui CY, Bykhovskaia M, Jagota A. Coarse-Grained Model of SNARE-Mediated Docking. Biophys J 2016; 108:2258-69. [PMID: 25954883 DOI: 10.1016/j.bpj.2015.03.053] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2014] [Revised: 03/24/2015] [Accepted: 03/24/2015] [Indexed: 12/11/2022] Open
Abstract
Synaptic transmission requires that vesicles filled with neurotransmitter molecules be docked to the plasma membrane by the SNARE protein complex. The SNARE complex applies attractive forces to overcome the long-range repulsion between the vesicle and membrane. To understand how the balance between the attractive and repulsive forces defines the equilibrium docked state we have developed a model that combines the mechanics of vesicle/membrane deformation with an apparently new coarse-grained model of the SNARE complex. The coarse-grained model of the SNARE complex is calibrated by comparison with all-atom molecular dynamics simulations as well as by force measurements in laser tweezer experiments. The model for vesicle/membrane interactions includes the forces produced by membrane deformation and hydration or electrostatic repulsion. Combining these two parts, the coarse-grained model of the SNARE complex with membrane mechanics, we study how the equilibrium docked state varies with the number of SNARE complexes. We find that a single SNARE complex is able to bring a typical synaptic vesicle to within a distance of ∼ 3 nm from the membrane. Further addition of SNARE complexes shortens this distance, but an overdocked state of >4-6 SNAREs actually increases the equilibrium distance.
Collapse
Affiliation(s)
- Nicole Fortoul
- Department of Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, Pennsylvania
| | - Pankaj Singh
- Department of Mechanical & Aerospace Engineering, Cornell University, Ithaca, New York
| | - Chung-Yuen Hui
- Department of Mechanical & Aerospace Engineering, Cornell University, Ithaca, New York
| | - Maria Bykhovskaia
- Neuroscience Department, Universidad Central del Caribe, Bayamon, Puerto Rico
| | - Anand Jagota
- Department of Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, Pennsylvania; Bioengineering Program, Lehigh University, Bethlehem, Pennsylvania.
| |
Collapse
|
49
|
A Post-Docking Role of Synaptotagmin 1-C2B Domain Bottom Residues R398/399 in Mouse Chromaffin Cells. J Neurosci 2016; 35:14172-82. [PMID: 26490858 DOI: 10.1523/jneurosci.1911-15.2015] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Synaptotagmin-1 (Syt1) is the principal Ca(2+) sensor for vesicle fusion and is also essential for vesicle docking in chromaffin cells. Docking depends on interactions of the Syt1-C2B domain with the t-SNARE SNAP25/Syntaxin1 complex and/or plasma membrane phospholipids. Here, we investigated the role of the positively charged "bottom" region of the C2B domain, proposed to help crosslink membranes, in vesicle docking and secretion in mouse chromaffin cells and in cell-free assays. We expressed a double mutation shown previously to interfere with lipid mixing between proteoliposomes and with synaptic transmission, Syt1-R398/399Q (RQ), in syt1 null mutant cells. Ultrastructural morphometry revealed that Syt1-RQ fully restored the docking defect observed previously in syt1 null mutant cells, similar to wild type Syt1 (Syt1-wt). Small unilamellar lipid vesicles (SUVs) that contained the v-SNARE Synaptobrevin2 and Syt1-R398/399Q also docked to t-SNARE-containing giant vesicles (GUVs), similar to Syt1-wt. However, unlike Syt1-wt, Syt1-RQ-induced docking was strictly PI(4,5)P2-dependent. Unlike docking, neither synchronized secretion in chromaffin cells nor Ca(2+)-triggered SUV-GUV fusion was restored by the Syt1 mutants. Finally, overexpressing the RQ-mutant in wild type cells produced no effect on either docking or secretion. We conclude that the positively charged bottom region in the C2B domain--and, by inference, Syt1-mediated membrane crosslinking--is required for triggering fusion, but not for docking. Secretory vesicles dock by multiple, PI(4,5)P2-dependent and PI(4,5)P2-independent mechanisms. The R398/399 mutations selectively disrupt the latter and hereby help to discriminate protein regions involved in different aspects of Syt1 function in docking and fusion. SIGNIFICANCE STATEMENT This study provides new insights in how the two opposite sides of the C2B domain of Synaptotagmin-1 participate in secretory vesicle fusion, and in more upstream steps, especially vesicle docking. We show that the "bottom" surface of the C2B domain is required for triggering fusion, but not for docking. Synaptotagmin-1 promotes docking by multiple, PI(4,5)P2-dependent and PI(4,5)P2-independent mechanisms. Mutations in the C2B bottom surface (R398/399) selectively disrupt the latter. These mutations help to discriminate protein regions involved in different aspects of Synaptotagmin-1 function in docking and fusion.
Collapse
|
50
|
Abstract
Extensive research has yielded crucial insights into the mechanism of neurotransmitter release, and working models for the functions of key proteins involved in release. The SNAREs Syntaxin-1, Synaptobrevin, and SNAP-25 play a central role in membrane fusion, forming SNARE complexes that bridge the vesicle and plasma membranes and that are disassembled by NSF-SNAPs. Exocytosis likely starts with Syntaxin-1 folded into a self-inhibited closed conformation that binds to Munc18-1. Munc13s open Syntaxin-1, orchestrating SNARE complex assembly in an NSF-SNAP-resistant manner together with Munc18-1. In the resulting primed state, with partially assembled SNARE complexes, fusion is inhibited by Synaptotagmin-1 and Complexins, which also perform active functions in release. Upon influx of Ca(2+), Synaptotagmin-1 activates fast release, likely by relieving the inhibition caused by Complexins and cooperating with the SNAREs in bringing the membranes together. Although alternative models exist and fundamental questions remain unanswered, a definitive description of the basic release mechanism may be available soon.
Collapse
Affiliation(s)
- Josep Rizo
- Departments of Biophysics, Biochemistry, and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390;
| | | |
Collapse
|