1
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Cerda-Jara CA, Kim SJ, Thomas G, Farsi Z, Zolotarov G, Dube G, Deter A, Bahry E, Georgii E, Woehler A, Piwecka M, Rajewsky N. miR-7 controls glutamatergic transmission and neuronal connectivity in a Cdr1as-dependent manner. EMBO Rep 2024; 25:3008-3039. [PMID: 38831125 PMCID: PMC11239925 DOI: 10.1038/s44319-024-00168-9] [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: 01/04/2024] [Revised: 04/12/2024] [Accepted: 05/14/2024] [Indexed: 06/05/2024] Open
Abstract
The circular RNA (circRNA) Cdr1as is conserved across mammals and highly expressed in neurons, where it directly interacts with microRNA miR-7. However, the biological function of this interaction is unknown. Here, using primary cortical murine neurons, we demonstrate that stimulating neurons by sustained depolarization rapidly induces two-fold transcriptional upregulation of Cdr1as and strong post-transcriptional stabilization of miR-7. Cdr1as loss causes doubling of glutamate release from stimulated synapses and increased frequency and duration of local neuronal bursts. Moreover, the periodicity of neuronal networks increases, and synchronicity is impaired. Strikingly, these effects are reverted by sustained expression of miR-7, which also clears Cdr1as molecules from neuronal projections. Consistently, without Cdr1as, transcriptomic changes caused by miR-7 overexpression are stronger (including miR-7-targets downregulation) and enriched in secretion/synaptic plasticity pathways. Altogether, our results suggest that in cortical neurons Cdr1as buffers miR-7 activity to control glutamatergic excitatory transmission and neuronal connectivity important for long-lasting synaptic adaptations.
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Affiliation(s)
- Cledi A Cerda-Jara
- Laboratory for Systems Biology of Gene Regulatory Elements, Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Hannoversche Str. 28, 10115, Berlin, Germany
| | - Seung Joon Kim
- Laboratory for Systems Biology of Gene Regulatory Elements, Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Hannoversche Str. 28, 10115, Berlin, Germany
| | - Gwendolin Thomas
- Laboratory for Systems Biology of Gene Regulatory Elements, Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Hannoversche Str. 28, 10115, Berlin, Germany
| | - Zohreh Farsi
- Light Microscopy Platform, Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Hannoversche Str. 28, 10115, Berlin, Germany
| | - Grygoriy Zolotarov
- Laboratory for Systems Biology of Gene Regulatory Elements, Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Hannoversche Str. 28, 10115, Berlin, Germany
| | - Giuliana Dube
- Laboratory for Systems Biology of Gene Regulatory Elements, Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Hannoversche Str. 28, 10115, Berlin, Germany
| | - Aylina Deter
- Laboratory for Systems Biology of Gene Regulatory Elements, Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Hannoversche Str. 28, 10115, Berlin, Germany
| | - Ella Bahry
- Helmholtz Imaging, Max-Delbrück-Center for Molecular Medicine, Berlin, Germany Hannoversche Str. 28, 10115, Berlin, Germany
| | - Elisabeth Georgii
- Helmholtz AI, Helmholtz Zentrum München, Ingolstädter Landstraße 1, D-85764, Neuherberg, Germany
| | - Andrew Woehler
- Light Microscopy Platform, Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Hannoversche Str. 28, 10115, Berlin, Germany
| | - Monika Piwecka
- Department of Non-Coding RNAs, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704, Poznan, Poland
| | - Nikolaus Rajewsky
- Laboratory for Systems Biology of Gene Regulatory Elements, Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Hannoversche Str. 28, 10115, Berlin, Germany.
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2
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Bose D, Bera M, Norman CA, Timofeeva Y, Volynski KE, Krishnakumar SS. A minimal presynaptic protein machinery mediating synchronous and asynchronous exocytosis and short-term plasticity. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.15.589559. [PMID: 38659918 PMCID: PMC11042279 DOI: 10.1101/2024.04.15.589559] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/26/2024]
Abstract
Neurotransmitters are released from synaptic vesicles with remarkable precision in response to presynaptic Ca2+ influx but exhibit significant heterogeneity in exocytosis timing and efficacy based on the recent history of activity. This heterogeneity is critical for information transfer in the brain, yet its molecular basis remains poorly understood. Here, we employ a biochemically-defined fusion assay under physiologically-relevant conditions to delineate the minimal protein machinery sufficient to account for different modes of Ca2+-triggered vesicle fusion and short-term facilitation. We find that Synaptotagmin-1, Synaptotagmin-7, and Complexin, synergistically restrain SNARE complex assembly, thus preserving vesicles in a stably docked state at rest. Upon Ca2+ activation, Synaptotagmin-1 induces rapid vesicle fusion, while Synaptotagmin-7 mediates delayed fusion. Competitive binding of Synaptotagmin-1 and Synaptotagmin-7 to the same SNAREs, coupled with differential rates of Ca2+-triggered fusion clamp reversal, govern the kinetics of vesicular fusion. Under conditions mimicking sustained neuronal activity, the Synaptotagmin-7 fusion clamp is destabilized by the elevated basal Ca2+ concentration, thereby enhancing the synchronous component of fusion. These findings provide a direct demonstration that a small set of proteins is sufficient to account for how nerve terminals adapt and regulate the Ca2+-evoked neurotransmitter exocytosis process to support their specialized functions in the nervous system.
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Affiliation(s)
- Dipayan Bose
- Yale Nanobiology Institute, Yale University School of Medicine, New Haven, USA
- Department of Neurology, Yale University School of Medicine, New Haven, USA
| | - Manindra Bera
- Yale Nanobiology Institute, Yale University School of Medicine, New Haven, USA
- Cell Biology, Yale University School of Medicine, New Haven, USA
| | - Chris A Norman
- Department of Clinical and Experimental Epilepsy, UCL Queen Square Institute of Neurology, University College London, UK
- Department of Computer Science, University of Warwick, Coventry, UK
| | - Yulia Timofeeva
- Department of Computer Science, University of Warwick, Coventry, UK
| | - Kirill E Volynski
- Cell Biology, Yale University School of Medicine, New Haven, USA
- Department of Clinical and Experimental Epilepsy, UCL Queen Square Institute of Neurology, University College London, UK
| | - Shyam S Krishnakumar
- Yale Nanobiology Institute, Yale University School of Medicine, New Haven, USA
- Department of Neurology, Yale University School of Medicine, New Haven, USA
- Department of Clinical and Experimental Epilepsy, UCL Queen Square Institute of Neurology, University College London, UK
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3
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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.
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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
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4
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Genge MG, Roy Chowdhury S, Dohnálek V, Yunoki K, Hirashima T, Endo T, Doležal P, Mokranjac D. Two domains of Tim50 coordinate translocation of proteins across the two mitochondrial membranes. Life Sci Alliance 2023; 6:e202302122. [PMID: 37748811 PMCID: PMC10520260 DOI: 10.26508/lsa.202302122] [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: 04/28/2023] [Revised: 09/13/2023] [Accepted: 09/14/2023] [Indexed: 09/27/2023] Open
Abstract
Hundreds of mitochondrial proteins with N-terminal presequences are translocated across the outer and inner mitochondrial membranes via the TOM and TIM23 complexes, respectively. How translocation of proteins across two mitochondrial membranes is coordinated is largely unknown. Here, we show that the two domains of Tim50 in the intermembrane space, named core and PBD, both have essential roles in this process. Building upon the surprising observation that the two domains of Tim50 can complement each other in trans, we establish that the core domain contains the main presequence-binding site and serves as the main recruitment point to the TIM23 complex. On the other hand, the PBD plays, directly or indirectly, a critical role in cooperation of the TOM and TIM23 complexes and supports the receptor function of Tim50. Thus, the two domains of Tim50 both have essential but distinct roles and together coordinate translocation of proteins across two mitochondrial membranes.
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Affiliation(s)
- Marcel G Genge
- Biocenter-Department of Cell Biology, LMU Munich, Munich, Germany
| | | | - Vít Dohnálek
- Department of Parasitology, Faculty of Science, Charles University, BIOCEV, Vestec, Czech Republic
| | - Kaori Yunoki
- Faculty of Life Sciences and Institute for Protein Dynamics, Kyoto Sangyo University, Kyoto, Japan
| | - Takashi Hirashima
- Faculty of Life Sciences and Institute for Protein Dynamics, Kyoto Sangyo University, Kyoto, Japan
| | - Toshiya Endo
- Faculty of Life Sciences and Institute for Protein Dynamics, Kyoto Sangyo University, Kyoto, Japan
| | - Pavel Doležal
- Department of Parasitology, Faculty of Science, Charles University, BIOCEV, Vestec, Czech Republic
| | - Dejana Mokranjac
- Biocenter-Department of Cell Biology, LMU Munich, Munich, Germany
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5
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Bera M, Radhakrishnan A, Coleman J, K. Sundaram RV, Ramakrishnan S, Pincet F, Rothman JE. Synaptophysin chaperones the assembly of 12 SNAREpins under each ready-release vesicle. Proc Natl Acad Sci U S A 2023; 120:e2311484120. [PMID: 37903271 PMCID: PMC10636311 DOI: 10.1073/pnas.2311484120] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Accepted: 09/19/2023] [Indexed: 11/01/2023] Open
Abstract
The synaptic vesicle protein Synaptophysin (Syp) has long been known to form a complex with the Vesicle associated soluble N-ethylmaleimide sensitive fusion protein attachment receptor (v-SNARE) Vesicle associated membrane protein (VAMP), but a more specific molecular function or mechanism of action in exocytosis has been lacking because gene knockouts have minimal effects. Utilizing fully defined reconstitution and single-molecule measurements, we now report that Syp functions as a chaperone that determines the number of SNAREpins assembling between a ready-release vesicle and its target membrane bilayer. Specifically, Syp directs the assembly of 12 ± 1 SNAREpins under each docked vesicle, even in the face of an excess of SNARE proteins. The SNAREpins assemble in successive waves of 6 ± 1 and 5 ± 2 SNAREpins, respectively, tightly linked to oligomerization of and binding to the vesicle Ca++ sensor Synaptotagmin. Templating of 12 SNAREpins by Syp is likely the direct result of its hexamer structure and its binding of VAMP2 dimers, both of which we demonstrate in detergent extracts and lipid bilayers.
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Affiliation(s)
- Manindra Bera
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Abhijith Radhakrishnan
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Jeff Coleman
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - R. Venkat K. Sundaram
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Sathish Ramakrishnan
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Pathology, Yale University School of Medicine, New Haven, CT06520
| | - Frederic Pincet
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, Paris Sciences et Lettres Research University, CNRS, Sorbonne Université, Université de Paris Cité, 75005Paris, France
| | - James E. Rothman
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
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6
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Rothman JE, Grushin K, Bera M, Pincet F. Turbocharging synaptic transmission. FEBS Lett 2023; 597:2233-2249. [PMID: 37643878 DOI: 10.1002/1873-3468.14718] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Revised: 07/07/2023] [Accepted: 07/11/2023] [Indexed: 08/31/2023]
Abstract
Evidence from biochemistry, genetics, and electron microscopy strongly supports the idea that a ring of Synaptotagmin is central to the clamping and release of synaptic vesicles (SVs) for synchronous neurotransmission. Recent direct measurements in cell-free systems suggest there are 12 SNAREpins in each ready-release vesicle, consisting of six peripheral and six central SNAREpins. The six central SNAREpins are directly bound to the Synaptotagmin ring, are directly released by Ca++ , and they initially open the fusion pore. The six peripheral SNAREpins are indirectly bound to the ring, each linked to a central SNAREpin by a bridging molecule of Complexin. We suggest that the primary role of peripheral SNAREpins is to provide additional force to 'turbocharge' neurotransmitter release, explaining how it can occur much faster than other forms of membrane fusion. The SV protein Synaptophysin forms hexamers that bear two copies of the v-SNARE VAMP at each vertex, one likely assembling into a peripheral SNAREpin and the other into a central SNAREpin.
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Affiliation(s)
- James E Rothman
- Nanobiology Institute and Department of Cell Biology, Yale University, New Haven, CT, USA
| | - Kirill Grushin
- Nanobiology Institute and Department of Cell Biology, Yale University, New Haven, CT, USA
| | - Manindra Bera
- Nanobiology Institute and Department of Cell Biology, Yale University, New Haven, CT, USA
| | - Frederic Pincet
- Nanobiology Institute and Department of Cell Biology, Yale University, New Haven, CT, USA
- Laboratoire de Physique de l'Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, Paris, France
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7
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Kalyana Sundaram RV, Chatterjee A, Bera M, Grushin K, Panda A, Li F, Coleman J, Lee S, Ramakrishnan S, Ernst AM, Gupta K, Rothman JE, Krishnakumar SS. Roles for diacylglycerol in synaptic vesicle priming and release revealed by complete reconstitution of core protein machinery. Proc Natl Acad Sci U S A 2023; 120:e2309516120. [PMID: 37590407 PMCID: PMC10450444 DOI: 10.1073/pnas.2309516120] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2023] [Accepted: 07/14/2023] [Indexed: 08/19/2023] Open
Abstract
Here, we introduce the full functional reconstitution of genetically validated core protein machinery (SNAREs, Munc13, Munc18, Synaptotagmin, and Complexin) for synaptic vesicle priming and release in a geometry that enables detailed characterization of the fate of docked vesicles both before and after release is triggered with Ca2+. Using this setup, we identify new roles for diacylglycerol (DAG) in regulating vesicle priming and Ca2+-triggered release involving the SNARE assembly chaperone Munc13. We find that low concentrations of DAG profoundly accelerate the rate of Ca2+-dependent release, and high concentrations reduce clamping and permit extensive spontaneous release. As expected, DAG also increases the number of docked, release-ready vesicles. Dynamic single-molecule imaging of Complexin binding to release-ready vesicles directly establishes that DAG accelerates the rate of SNAREpin assembly mediated by chaperones, Munc13 and Munc18. The selective effects of physiologically validated mutations confirmed that the Munc18-Syntaxin-VAMP2 "template" complex is a functional intermediate in the production of primed, release-ready vesicles, which requires the coordinated action of Munc13 and Munc18.
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Affiliation(s)
- R. Venkat Kalyana Sundaram
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Atrouli Chatterjee
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Manindra Bera
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Kirill Grushin
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Aniruddha Panda
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Feng Li
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Jeff Coleman
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Seong Lee
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Sathish Ramakrishnan
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Pathology, Yale University School of Medicine, New Haven, CT06520
| | - Andreas M. Ernst
- School of Biological Sciences, University of California San Diego, San Diego, CA92093
| | - Kallol Gupta
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - James E. Rothman
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT06520
| | - Shyam S. Krishnakumar
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT06520
- Department of Neurology, Yale University School of Medicine, New Haven, CT06520
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8
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Bera M, Radhakrishnan A, Coleman J, Sundaram RVK, Ramakrishnan S, Pincet F, Rothman JE. Synaptophysin Chaperones the Assembly of 12 SNAREpins under each Ready-Release Vesicle. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.05.547834. [PMID: 37461465 PMCID: PMC10349951 DOI: 10.1101/2023.07.05.547834] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 07/24/2023]
Abstract
The synaptic vesicle protein Synaptophysin has long been known to form a complex with the v-SNARE VAMP, but a more specific molecular function or mechanism of action in exocytosis has been lacking because gene knockouts have minimal effects. Utilizing fully-defined reconstitution and single-molecule measurements, we now report that Synaptophysin functions as a chaperone that determines the number of SNAREpins assembling between a ready-release vesicle and its target membrane bilayer. Specifically, Synaptophysin directs the assembly of 12 ± 1 SNAREpins under each docked vesicle, even in the face of an excess of SNARE proteins. The SNAREpins assemble in successive waves of 6 ± 1 and 5 ± 2 SNAREpins, respectively, tightly linked to oligomerization of and binding to the vesicle Ca++ sensor Synaptotagmin. Templating of 12 SNAREpins by Synaptophysin is likely the direct result of its hexamer structure and its binding of VAMP2 dimers, both of which we demonstrate in detergent extracts and lipid bilayers.
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Affiliation(s)
- Manindra Bera
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Abhijith Radhakrishnan
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Jeff Coleman
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Ramalingam Venkat Kalyana Sundaram
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Sathish Ramakrishnan
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Pathology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Frederic Pincet
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
- Laboratoire de Physique de l’Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, Paris, France
| | - James E. Rothman
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
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9
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Sundaram RVK, Chatterjee A, Bera M, Grushin K, Panda A, Li F, Coleman J, Lee S, Ramakrishnan S, Ernst AM, Gupta K, Rothman JE, Krishnakumar SS. Novel Roles for Diacylglycerol in Synaptic Vesicle Priming and Release Revealed by Complete Reconstitution of Core Protein Machinery. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.05.543781. [PMID: 37333317 PMCID: PMC10274626 DOI: 10.1101/2023.06.05.543781] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/20/2023]
Abstract
Here we introduce the full functional reconstitution of genetically-validated core protein machinery (SNAREs, Munc13, Munc18, Synaptotagmin, Complexin) for synaptic vesicle priming and release in a geometry that enables detailed characterization of the fate of docked vesicles both before and after release is triggered with Ca 2+ . Using this novel setup, we discover new roles for diacylglycerol (DAG) in regulating vesicle priming and Ca 2+- triggered release involving the SNARE assembly chaperone Munc13. We find that low concentrations of DAG profoundly accelerate the rate of Ca 2+ -dependent release, and high concentrations reduce clamping and permit extensive spontaneous release. As expected, DAG also increases the number of ready-release vesicles. Dynamic single-molecule imaging of Complexin binding to ready-release vesicles directly establishes that DAG accelerates the rate of SNAREpin assembly mediated by Munc13 and Munc18 chaperones. The selective effects of physiologically validated mutations confirmed that the Munc18-Syntaxin-VAMP2 'template' complex is a functional intermediate in the production of primed, ready-release vesicles, which requires the coordinated action of Munc13 and Munc18. SIGNIFICANCE STATEMENT Munc13 and Munc18 are SNARE-associated chaperones that act as "priming" factors, facilitating the formation of a pool of docked, release-ready vesicles and regulating Ca 2+ -evoked neurotransmitter release. Although important insights into Munc18/Munc13 function have been gained, how they assemble and operate together remains enigmatic. To address this, we developed a novel biochemically-defined fusion assay which enabled us to investigate the cooperative action of Munc13 and Munc18 in molecular terms. We find that Munc18 nucleates the SNARE complex, while Munc13 promotes and accelerates the SNARE assembly in a DAG-dependent manner. The concerted action of Munc13 and Munc18 stages the SNARE assembly process to ensure efficient 'clamping' and formation of stably docked vesicles, which can be triggered to fuse rapidly (∼10 msec) upon Ca 2+ influx.
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Affiliation(s)
- R Venkat Kalyana Sundaram
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Atrouli Chatterjee
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Manindra Bera
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Kirill Grushin
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Aniruddha Panda
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Feng Li
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Jeff Coleman
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Seong Lee
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Sathish Ramakrishnan
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Pathology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Andreas M. Ernst
- School of Biological Sciences, University of California San Diego, La Jolla CA 92093, USA
| | - Kallol Gupta
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - James E. Rothman
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Shyam S. Krishnakumar
- Nanobiology Institute, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06520, USA
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10
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Bykhovskaia M. Molecular Dynamics Simulations of the Proteins Regulating Synaptic Vesicle Fusion. MEMBRANES 2023; 13:307. [PMID: 36984694 PMCID: PMC10058449 DOI: 10.3390/membranes13030307] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/23/2023] [Revised: 02/11/2023] [Accepted: 03/01/2023] [Indexed: 06/18/2023]
Abstract
Neuronal transmitters are packaged in synaptic vesicles (SVs) and released by the fusion of SVs with the presynaptic membrane (PM). An inflow of Ca2+ into the nerve terminal triggers fusion, and the SV-associated protein Synaptotagmin 1 (Syt1) serves as a Ca2+ sensor. In preparation for fusion, SVs become attached to the PM by the SNARE protein complex, a coiled-coil bundle that exerts the force overcoming SV-PM repulsion. A cytosolic protein Complexin (Cpx) attaches to the SNARE complex and differentially regulates the evoked and spontaneous release components. It is still debated how the dynamic interactions of Syt1, SNARE proteins and Cpx lead to fusion. This problem is confounded by heterogeneity in the conformational states of the prefusion protein-lipid complex and by the lack of tools to experimentally monitor the rapid conformational transitions of the complex, which occur at a sub-millisecond scale. However, these complications can be overcome employing molecular dynamics (MDs), a computational approach that enables simulating interactions and conformational transitions of proteins and lipids. This review discusses the use of molecular dynamics for the investigation of the pre-fusion protein-lipid complex. We discuss the dynamics of the SNARE complex between lipid bilayers, as well as the interactions of Syt1 with lipids and SNARE proteins, and Cpx regulating the assembly of the SNARE complex.
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Affiliation(s)
- Maria Bykhovskaia
- Neurology Department, Wayne State University, Detroit, MI 48202, USA
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11
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Lévêque C, Maulet Y, Wang Q, Rame M, Rodriguez L, Mochida S, Sangiardi M, Youssouf F, Iborra C, Seagar M, Vitale N, El Far O. A Role for the V0 Sector of the V-ATPase in Neuroexocytosis: Exogenous V0d Blocks Complexin and SNARE Interactions with V0c. Cells 2023; 12:cells12050750. [PMID: 36899886 PMCID: PMC10001230 DOI: 10.3390/cells12050750] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Revised: 02/23/2023] [Accepted: 02/24/2023] [Indexed: 03/03/2023] Open
Abstract
V-ATPase is an important factor in synaptic vesicle acidification and is implicated in synaptic transmission. Rotation in the extra-membranous V1 sector drives proton transfer through the membrane-embedded multi-subunit V0 sector of the V-ATPase. Intra-vesicular protons are then used to drive neurotransmitter uptake by synaptic vesicles. V0a and V0c, two membrane subunits of the V0 sector, have been shown to interact with SNARE proteins, and their photo-inactivation rapidly impairs synaptic transmission. V0d, a soluble subunit of the V0 sector strongly interacts with its membrane-embedded subunits and is crucial for the canonic proton transfer activity of the V-ATPase. Our investigations show that the loop 1.2 of V0c interacts with complexin, a major partner of the SNARE machinery and that V0d1 binding to V0c inhibits this interaction, as well as V0c association with SNARE complex. The injection of recombinant V0d1 in rat superior cervical ganglion neurons rapidly reduced neurotransmission. In chromaffin cells, V0d1 overexpression and V0c silencing modified in a comparable manner several parameters of unitary exocytotic events. Our data suggest that V0c subunit promotes exocytosis via interactions with complexin and SNAREs and that this activity can be antagonized by exogenous V0d.
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Affiliation(s)
- Christian Lévêque
- INSERM UMR_S 1072, 13015 Marseille, France
- Aix-Marseille Université, 13015 Marseille, France
| | - Yves Maulet
- INSERM UMR_S 1072, 13015 Marseille, France
- Aix-Marseille Université, 13015 Marseille, France
| | - Qili Wang
- Institut des Neurosciences Cellulaires et Intégratives, Centre National de la Recherche Scientifique, Université de Strasbourg, 67000 Strasbourg, France
| | - Marion Rame
- Institut des Neurosciences Cellulaires et Intégratives, Centre National de la Recherche Scientifique, Université de Strasbourg, 67000 Strasbourg, France
| | - Léa Rodriguez
- INSERM UMR_S 1072, 13015 Marseille, France
- Aix-Marseille Université, 13015 Marseille, France
| | - Sumiko Mochida
- Department of Physiology, Tokyo Medical University, Tokyo 160-8402, Japan
| | - Marion Sangiardi
- INSERM UMR_S 1072, 13015 Marseille, France
- Aix-Marseille Université, 13015 Marseille, France
| | - Fahamoe Youssouf
- INSERM UMR_S 1072, 13015 Marseille, France
- Aix-Marseille Université, 13015 Marseille, France
| | - Cécile Iborra
- INSERM UMR_S 1072, 13015 Marseille, France
- Aix-Marseille Université, 13015 Marseille, France
| | - Michael Seagar
- INSERM UMR_S 1072, 13015 Marseille, France
- Aix-Marseille Université, 13015 Marseille, France
| | - Nicolas Vitale
- Institut des Neurosciences Cellulaires et Intégratives, Centre National de la Recherche Scientifique, Université de Strasbourg, 67000 Strasbourg, France
- Correspondence: (N.V.); or (O.E.F.); Tel.: +33-(0)3-8845-6712 (N.V.); +33-(0)4-9169-8860 (O.E.F.)
| | - Oussama El Far
- INSERM UMR_S 1072, 13015 Marseille, France
- Aix-Marseille Université, 13015 Marseille, France
- Correspondence: (N.V.); or (O.E.F.); Tel.: +33-(0)3-8845-6712 (N.V.); +33-(0)4-9169-8860 (O.E.F.)
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12
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Hesselbarth J, Schmidt C. Mass spectrometry uncovers intermediates and off-pathway complexes for SNARE complex assembly. Commun Biol 2023; 6:198. [PMID: 36806321 PMCID: PMC9941103 DOI: 10.1038/s42003-023-04548-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Accepted: 02/01/2023] [Indexed: 02/22/2023] Open
Abstract
The SNARE complex assembles from vesicular Synaptobrevin-2 as well as Syntaxin-1 and SNAP25 both anchored to the presynaptic membrane. It mediates fusion of synaptic vesicles with the presynaptic plasma membrane resulting in exocytosis of neurotransmitters. While the general sequence of SNARE complex formation is well-established, our knowledge on possible intermediates and stable off-pathway complexes is incomplete. We, therefore, follow the stepwise assembly of the SNARE complex and target individual SNAREs, binary sub-complexes, the ternary SNARE complex as well as interactions with Complexin-1. Using native mass spectrometry, we identify the stoichiometry of sub-complexes and monitor oligomerisation of various assemblies. Importantly, we find that interactions with Complexin-1 reduce multimerisation of the ternary SNARE complex. Chemical cross-linking provides detailed insights into these interactions suggesting a role for membrane fusion. In summary, we unravel the stoichiometry of intermediates and off-pathway complexes and compile a road map of SNARE complex assembly including regulation by Complexin-1.
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Affiliation(s)
- Julia Hesselbarth
- Interdisciplinary Research Centre HALOmem, Charles Tanford Protein Centre, Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Halle, Germany
- Department of Chemistry - Biochemistry, Biocenter II, Johannes Gutenberg University Mainz, Mainz, Germany
| | - Carla Schmidt
- Interdisciplinary Research Centre HALOmem, Charles Tanford Protein Centre, Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Halle, Germany.
- Department of Chemistry - Biochemistry, Biocenter II, Johannes Gutenberg University Mainz, Mainz, Germany.
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13
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Hao T, Feng N, Gong F, Yu Y, Liu J, Ren YX. Complexin-1 regulated assembly of single neuronal SNARE complex revealed by single-molecule optical tweezers. Commun Biol 2023; 6:155. [PMID: 36750663 PMCID: PMC9905088 DOI: 10.1038/s42003-023-04506-w] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2022] [Accepted: 01/19/2023] [Indexed: 02/09/2023] Open
Abstract
The dynamic assembly of the Synaptic-soluble N-ethylmaleimide-sensitive factor Attachment REceptor (SNARE) complex is crucial to understand membrane fusion. Traditional ensemble study meets the challenge to dissect the dynamic assembly of the protein complex. Here, we apply minute force on a tethered protein complex through dual-trap optical tweezers and study the folding dynamics of SNARE complex under mechanical force regulated by complexin-1 (CpxI). We reconstruct the clamp and facilitate functions of CpxI in vitro and identify different interplay mechanism of CpxI fragment binding on the SNARE complex. Specially, while the N-terminal domain (NTD) plays a dominant role of the facilitate function, CTD is mainly related to clamping. And the mixture of 1-83aa and CTD of CpxI can efficiently reconstitute the inhibitory signal identical to that the full-length CpxI functions. Our observation identifies the important chaperone role of the CpxI molecule in the dynamic assembly of SNARE complex under mechanical tension, and elucidates the specific function of each fragment of CpxI molecules in the chaperone process.
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Affiliation(s)
- Tongrui Hao
- State Key Laboratory of Molecular Biology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Science, Shanghai, 200031, China. .,University of Chinese Academy of Sciences, Beijing, 200049, China.
| | - Nan Feng
- grid.9227.e0000000119573309State Key Laboratory of Molecular Biology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Science, Shanghai, 200031 China ,grid.410726.60000 0004 1797 8419University of Chinese Academy of Sciences, Beijing, 200049 China
| | - Fan Gong
- grid.9227.e0000000119573309National Facility for Protein Science in Shanghai, Zhangjiang Lab, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai, 201210 China
| | - Yang Yu
- grid.9227.e0000000119573309National Facility for Protein Science in Shanghai, Zhangjiang Lab, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai, 201210 China
| | - Jiaquan Liu
- State Key Laboratory of Molecular Biology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Science, Shanghai, 200031, China.
| | - Yu-Xuan Ren
- Institute for Translational Brain Research, Shanghai Medical College, Fudan University, Shanghai, 200032, China.
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14
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Grasso EM, Terakawa MS, Lai AL, Xue Xie Y, Ramlall TF, Freed JH, Eliezer D. Membrane Binding Induces Distinct Structural Signatures in the Mouse Complexin-1C-Terminal Domain. J Mol Biol 2023; 435:167710. [PMID: 35777466 PMCID: PMC9794636 DOI: 10.1016/j.jmb.2022.167710] [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: 05/10/2022] [Revised: 06/24/2022] [Accepted: 06/24/2022] [Indexed: 02/04/2023]
Abstract
Complexins play a critical role in regulating SNARE-mediated exocytosis of synaptic vesicles. Evolutionary divergences in complexin function have complicated our understanding of the role these proteins play in inhibiting the spontaneous fusion of vesicles. Previous structural and functional characterizations of worm and mouse complexins have indicated the membrane curvature-sensing C-terminal domain of these proteins is responsible for differences in inhibitory function. We have characterized the structure and dynamics of the mCpx1 CTD in the absence and presence of membranes and membrane mimetics using NMR, ESR, and optical spectroscopies. In the absence of lipids, the mCpx1 CTD features a short helix near its N-terminus and is otherwise disordered. In the presence of micelles and small unilamellar vesicles, the mCpx1 CTD forms a discontinuous helical structure in its C-terminal 20 amino acids, with no preference for specific lipid compositions. In contrast, the mCpx1 CTD shows distinct compositional preferences in its interactions with large unilamellar vesicles. These studies identify structural divergences in the mCpx1 CTD relative to the wCpx1 CTD in regions that are known to be critical to the wCpx1 CTD's role in inhibiting spontaneous fusion of synaptic vesicles, suggesting a potential structural basis for evolutionary divergences in complexin function.1.
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Affiliation(s)
- Emily M Grasso
- Department of Biochemistry, Weill Cornell Medicine, New York, NY, United States
| | - Mayu S Terakawa
- Department of Biochemistry, Weill Cornell Medicine, New York, NY, United States
| | - Alex L Lai
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, United States
| | - Ying Xue Xie
- Department of Biochemistry, Weill Cornell Medicine, New York, NY, United States
| | - Trudy F Ramlall
- Department of Biochemistry, Weill Cornell Medicine, New York, NY, United States
| | - Jack H Freed
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, United States
| | - David Eliezer
- Department of Biochemistry, Weill Cornell Medicine, New York, NY, United States
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15
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Lottermoser JA, Dittman JS. Complexin Membrane Interactions: Implications for Synapse Evolution and Function. J Mol Biol 2023; 435:167774. [PMID: 35931110 PMCID: PMC9807284 DOI: 10.1016/j.jmb.2022.167774] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Revised: 07/27/2022] [Accepted: 07/28/2022] [Indexed: 02/04/2023]
Abstract
The molecules and mechanisms behind chemical synaptic transmission have been explored for decades. For several of the core proteins involved in synaptic vesicle fusion, we now have a reasonably detailed grasp of their biochemical, structural, and functional properties. Complexin is one of the key synaptic proteins for which a simple mechanistic understanding is still lacking. Living up to its name, this small protein has been associated with a variety of roles differing between synapses and between species, but little consensus has been reached on its fundamental modes of action. Much attention has been paid to its deeply conserved SNARE-binding properties, while membrane-binding features of complexin and their functional significance have yet to be explored to the same degree. In this review, we summarize the known membrane interactions of the complexin C-terminal domain and their potential relevance to its function, synaptic localization, and evolutionary history.
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Affiliation(s)
| | - Jeremy S Dittman
- Department of Biochemistry, Weill Cornell Medicine, New York, NY, United States.
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16
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Cui L, Li H, Xi Y, Hu Q, Liu H, Fan J, Xiang Y, Zhang X, Shui W, Lai Y. Vesicle trafficking and vesicle fusion: mechanisms, biological functions, and their implications for potential disease therapy. MOLECULAR BIOMEDICINE 2022; 3:29. [PMID: 36129576 PMCID: PMC9492833 DOI: 10.1186/s43556-022-00090-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Accepted: 07/12/2022] [Indexed: 11/10/2022] Open
Abstract
Intracellular vesicle trafficking is the fundamental process to maintain the homeostasis of membrane-enclosed organelles in eukaryotic cells. These organelles transport cargo from the donor membrane to the target membrane through the cargo containing vesicles. Vesicle trafficking pathway includes vesicle formation from the donor membrane, vesicle transport, and vesicle fusion with the target membrane. Coat protein mediated vesicle formation is a delicate membrane budding process for cargo molecules selection and package into vesicle carriers. Vesicle transport is a dynamic and specific process for the cargo containing vesicles translocation from the donor membrane to the target membrane. This process requires a group of conserved proteins such as Rab GTPases, motor adaptors, and motor proteins to ensure vesicle transport along cytoskeletal track. Soluble N-ethyl-maleimide-sensitive factor (NSF) attachment protein receptors (SNARE)-mediated vesicle fusion is the final process for vesicle unloading the cargo molecules at the target membrane. To ensure vesicle fusion occurring at a defined position and time pattern in eukaryotic cell, multiple fusogenic proteins, such as synaptotagmin (Syt), complexin (Cpx), Munc13, Munc18 and other tethering factors, cooperate together to precisely regulate the process of vesicle fusion. Dysfunctions of the fusogenic proteins in SNARE-mediated vesicle fusion are closely related to many diseases. Recent studies have suggested that stimulated membrane fusion can be manipulated pharmacologically via disruption the interface between the SNARE complex and Ca2+ sensor protein. Here, we summarize recent insights into the molecular mechanisms of vesicle trafficking, and implications for the development of new therapeutics based on the manipulation of vesicle fusion.
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17
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Rizo J, David G, Fealey ME, Jaczynska K. On the difficulties of characterizing weak protein interactions that are critical for neurotransmitter release. FEBS Open Bio 2022; 12:1912-1938. [PMID: 35986639 PMCID: PMC9623538 DOI: 10.1002/2211-5463.13473] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Revised: 08/09/2022] [Accepted: 08/18/2022] [Indexed: 01/25/2023] Open
Abstract
The mechanism of neurotransmitter release has been extensively characterized, showing that vesicle fusion is mediated by the SNARE complex formed by syntaxin-1, SNAP-25 and synaptobrevin. This complex is disassembled by N-ethylmaleimide sensitive factor (NSF) and SNAPs to recycle the SNAREs, whereas Munc18-1 and Munc13s organize SNARE complex assembly in an NSF-SNAP-resistant manner. Synaptotagmin-1 acts as the Ca2+ sensor that triggers exocytosis in a tight interplay with the SNAREs and complexins. Here, we review technical aspects associated with investigation of protein interactions underlying these steps, which is hindered because the release machinery is assembled between two membranes and is highly dynamic. Moreover, weak interactions, which are difficult to characterize, play key roles in neurotransmitter release, for instance by lowering energy barriers that need to be overcome in this highly regulated process. We illustrate the crucial role that structural biology has played in uncovering mechanisms underlying neurotransmitter release, but also discuss the importance of considering the limitations of the techniques used, including lessons learned from research in our lab and others. In particular, we emphasize: (a) the promiscuity of some protein sequences, including membrane-binding regions that can mediate irrelevant interactions with proteins in the absence of their native targets; (b) the need to ensure that weak interactions observed in crystal structures are biologically relevant; and (c) the limitations of isothermal titration calorimetry to analyze weak interactions. Finally, we stress that even studies that required re-interpretation often helped to move the field forward by improving our understanding of the system and providing testable hypotheses.
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Affiliation(s)
- Josep Rizo
- Department of BiophysicsUniversity of Texas Southwestern Medical CenterDallasTXUSA,Department of BiochemistryUniversity of Texas Southwestern Medical CenterDallasTXUSA,Department of PharmacologyUniversity of Texas Southwestern Medical CenterDallasTXUSA
| | - Guillaume David
- Department of BiophysicsUniversity of Texas Southwestern Medical CenterDallasTXUSA,Department of BiochemistryUniversity of Texas Southwestern Medical CenterDallasTXUSA,Department of PharmacologyUniversity of Texas Southwestern Medical CenterDallasTXUSA
| | - Michael E. Fealey
- Department of BiophysicsUniversity of Texas Southwestern Medical CenterDallasTXUSA,Department of BiochemistryUniversity of Texas Southwestern Medical CenterDallasTXUSA,Department of PharmacologyUniversity of Texas Southwestern Medical CenterDallasTXUSA
| | - Klaudia Jaczynska
- Department of BiophysicsUniversity of Texas Southwestern Medical CenterDallasTXUSA,Department of BiochemistryUniversity of Texas Southwestern Medical CenterDallasTXUSA,Department of PharmacologyUniversity of Texas Southwestern Medical CenterDallasTXUSA
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18
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Wang S, Ma C. Stability profile of the neuronal SNARE complex reflects its potency to drive fast membrane fusion. Biophys J 2022; 121:3081-3102. [PMID: 35810329 PMCID: PMC9463651 DOI: 10.1016/j.bpj.2022.07.013] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2022] [Revised: 05/24/2022] [Accepted: 07/07/2022] [Indexed: 11/02/2022] Open
Abstract
Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) form the SNARE complex to mediate most fusion events of the secretory pathway. The neuronal SNARE complex is featured by its high stability and half-zippered conformation required for driving robust and fast synaptic exocytosis. However, these two features seem to be thermodynamically mutually exclusive. In this study, we have employed temperature-dependent disassociation assays and single-molecule Förster resonance energy transfer (FRET) experiments to analyze the stability and conformation of the neuronal SNARE complex. We reclassified the amino acids of the SNARE motif into four sub-groups (core, core-side I and II, and non-contact). Our data showed that the core residues predominantly contribute to the complex stability to meet a basal requirement for SNARE-mediated membrane fusion, while the core-side residues exert an unbalanced effect on the N- and C-half bundle stability that determines the half-zippered conformation of the neuronal SNARE complex, which would accommodate essential regulations by complexins and synaptotagmins for fast Ca2+-triggered membrane fusion. Furthermore, our data confirmed a strong coupling of folding energy between the N- and C-half assembly of the neuronal SNARE complex, which rationalizes the strong potency of the half-zippered conformation to conduct robust and fast fusion. Overall, these results uncovered that the stability profile of the neuronal SNARE complex reflects its potency to drive fast and robust membrane fusion. Based on these results, we also developed a new parameter, the stability factor (Fs), to characterize the overall stability of the neuronal SNARE complex and resolved a linear correlation between the stability and inter-residue coulombic interactions of the neuronal SNARE complex, which would help rationally design artificial SNARE complexes and remold functional SNARE complexes with desirable stability.
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Affiliation(s)
- Shen Wang
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Cong Ma
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China.
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19
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Davis LA, Fogarty MJ, Brown A, Sieck GC. Structure and Function of the Mammalian Neuromuscular Junction. Compr Physiol 2022; 12:3731-3766. [PMID: 35950651 PMCID: PMC10461538 DOI: 10.1002/cphy.c210022] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The mammalian neuromuscular junction (NMJ) comprises a presynaptic terminal, a postsynaptic receptor region on the muscle fiber (endplate), and the perisynaptic (terminal) Schwann cell. As with any synapse, the purpose of the NMJ is to transmit signals from the nervous system to muscle fibers. This neural control of muscle fibers is organized as motor units, which display distinct structural and functional phenotypes including differences in pre- and postsynaptic elements of NMJs. Motor units vary considerably in the frequency of their activation (both motor neuron discharge rate and duration/duty cycle), force generation, and susceptibility to fatigue. For earlier and more frequently recruited motor units, the structure and function of the activated NMJs must have high fidelity to ensure consistent activation and continued contractile response to sustain vital motor behaviors (e.g., breathing and postural balance). Similarly, for higher force less frequent behaviors (e.g., coughing and jumping), the structure and function of recruited NMJs must ensure short-term reliable activation but not activation sustained for a prolonged period in which fatigue may occur. The NMJ is highly plastic, changing structurally and functionally throughout the life span from embryonic development to old age. The NMJ also changes under pathological conditions including acute and chronic disease. Such neuroplasticity often varies across motor unit types. © 2022 American Physiological Society. Compr Physiol 12:1-36, 2022.
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Affiliation(s)
- Leah A. Davis
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Matthew J. Fogarty
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Alyssa Brown
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Gary C. Sieck
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
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20
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Rizo J, Sari L, Qi Y, Im W, Lin MM. All-atom molecular dynamics simulations of Synaptotagmin-SNARE-complexin complexes bridging a vesicle and a flat lipid bilayer. eLife 2022; 11:76356. [PMID: 35708237 PMCID: PMC9239685 DOI: 10.7554/elife.76356] [Citation(s) in RCA: 27] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Accepted: 06/15/2022] [Indexed: 12/14/2022] Open
Abstract
Synaptic vesicles are primed into a state that is ready for fast neurotransmitter release upon Ca2+-binding to Synaptotagmin-1. This state likely includes trans-SNARE complexes between the vesicle and plasma membranes that are bound to Synaptotagmin-1 and complexins. However, the nature of this state and the steps leading to membrane fusion are unclear, in part because of the difficulty of studying this dynamic process experimentally. To shed light into these questions, we performed all-atom molecular dynamics simulations of systems containing trans-SNARE complexes between two flat bilayers or a vesicle and a flat bilayer with or without fragments of Synaptotagmin-1 and/or complexin-1. Our results need to be interpreted with caution because of the limited simulation times and the absence of key components, but suggest mechanistic features that may control release and help visualize potential states of the primed Synaptotagmin-1-SNARE-complexin-1 complex. The simulations suggest that SNAREs alone induce formation of extended membrane-membrane contact interfaces that may fuse slowly, and that the primed state contains macromolecular assemblies of trans-SNARE complexes bound to the Synaptotagmin-1 C2B domain and complexin-1 in a spring-loaded configuration that prevents premature membrane merger and formation of extended interfaces, but keeps the system ready for fast fusion upon Ca2+ influx.
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Affiliation(s)
- Josep Rizo
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, United States.,Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Levent Sari
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, United States.,Green Center for Systems Biology, The University of Texas Southwestern Medical Center, Dallas, United States
| | - Yife Qi
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, Shanghai, China
| | - Wonpil Im
- Department of Biological Sciences, Lehigh University, Bethlehem, United States.,Department of Chemistry, Lehigh University, Bethlehem, United States.,Department of Bioengineering, Lehigh University, Bethlehem, United States.,Department of Computer Science and Engineering, Lehigh University, Bethlehem, United States
| | - Milo M Lin
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, United States.,Green Center for Systems Biology, The University of Texas Southwestern Medical Center, Dallas, United States
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21
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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.
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Affiliation(s)
- Josep Rizo
- Departments of Biophysics, Biochemistry, and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, USA;
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22
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Bera M, Ramakrishnan S, Coleman J, Krishnakumar SS, Rothman JE. Molecular determinants of complexin clamping and activation function. eLife 2022; 11:e71938. [PMID: 35442188 PMCID: PMC9020821 DOI: 10.7554/elife.71938] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Accepted: 03/15/2022] [Indexed: 11/13/2022] Open
Abstract
Previously we reported that Synaptotagmin-1 and Complexin synergistically clamp the SNARE assembly process to generate and maintain a pool of docked vesicles that fuse rapidly and synchronously upon Ca2+ influx (Ramakrishnan et al., 2020). Here, using the same in vitro single-vesicle fusion assay, we determine the molecular details of the Complexin-mediated fusion clamp and its role in Ca2+-activation. We find that a delay in fusion kinetics, likely imparted by Synaptotagmin-1, is needed for Complexin to block fusion. Systematic truncation/mutational analyses reveal that continuous alpha-helical accessory-central domains of Complexin are essential for its inhibitory function and specific interaction of the accessory helix with the SNAREpins enhances this functionality. The C-terminal domain promotes clamping by locally elevating Complexin concentration through interactions with the membrane. Independent of their clamping functions, the accessory-central helical domains of Complexin also contribute to rapid Ca2+-synchronized vesicle release by increasing the probability of fusion from the clamped state.
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Affiliation(s)
- Manindra Bera
- Yale Nanobiology InstituteNew HavenUnited States
- Department of Cell Biology, Yale University School of MedicineNew HavenUnited States
| | - Sathish Ramakrishnan
- Yale Nanobiology InstituteNew HavenUnited States
- Department of Pathology, Yale University School of MedicineNew HavenUnited States
| | - Jeff Coleman
- Yale Nanobiology InstituteNew HavenUnited States
- Department of Cell Biology, Yale University School of MedicineNew HavenUnited States
| | - Shyam S Krishnakumar
- Yale Nanobiology InstituteNew HavenUnited States
- Departments of Neurology, Yale University School of MedicineNew HavenUnited States
| | - James E Rothman
- Yale Nanobiology InstituteNew HavenUnited States
- Department of Cell Biology, Yale University School of MedicineNew HavenUnited States
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Transfer RNA-Derived Fragments and isomiRs Are Novel Components of Chronic TBI-Induced Neuropathology. Biomedicines 2022; 10:biomedicines10010136. [PMID: 35052815 PMCID: PMC8773447 DOI: 10.3390/biomedicines10010136] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2021] [Revised: 12/31/2021] [Accepted: 01/04/2022] [Indexed: 02/04/2023] Open
Abstract
Neuroinflammation is a secondary injury mechanism that evolves in the brain for months after traumatic brain injury (TBI). We hypothesized that an altered small non-coding RNA (sncRNA) signature plays a key role in modulating post-TBI secondary injury and neuroinflammation. At 3threemonths post-TBI, messenger RNA sequencing (seq) and small RNAseq were performed on samples from the ipsilateral thalamus and perilesional cortex of selected rats with a chronic inflammatory endophenotype, and sham-operated controls. The small RNAseq identified dysregulation of 2 and 19 miRNAs in the thalamus and cortex, respectively. The two candidates from the thalamus and the top ten from the cortex were selected for validation. In the thalamus, miR-146a-5p and miR-155-5p levels were upregulated, and in the cortex, miR-375-3p and miR-211-5p levels were upregulated. Analysis of isomiRs of differentially expressed miRNAs identified 3′ nucleotide additions that were increased after TBI. Surprisingly, we found fragments originating from 16 and 13 tRNAs in the thalamus and cortex, respectively. We further analyzed two upregulated fragments, 3′tRF-IleAAT and 3′tRF-LysTTT. Increased expression of the full miR-146a profile, and 3′tRF-IleAAT and 3′tRF-LysTTT was associated with a worse behavioral outcome in animals with chronic neuroinflammation. Our results highlight the importance of understanding the regulatory roles of as-yet unknown sncRNAs for developing better strategies to treat TBI and neuroinflammation.
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24
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Szule JA. Hypothesis Relating the Structure, Biochemistry and Function of Active Zone Material Macromolecules at a Neuromuscular Junction. Front Synaptic Neurosci 2022; 13:798225. [PMID: 35069169 PMCID: PMC8766674 DOI: 10.3389/fnsyn.2021.798225] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Accepted: 12/14/2021] [Indexed: 12/22/2022] Open
Abstract
This report integrates knowledge of in situ macromolecular structures and synaptic protein biochemistry to propose a unified hypothesis for the regulation of certain vesicle trafficking events (i.e., docking, priming, Ca2+-triggering, and membrane fusion) that lead to neurotransmitter secretion from specialized “active zones” of presynaptic axon terminals. Advancements in electron tomography, to image tissue sections in 3D at nanometer scale resolution, have led to structural characterizations of a network of different classes of macromolecules at the active zone, called “Active Zone Material’. At frog neuromuscular junctions, the classes of Active Zone Material macromolecules “top-masts”, “booms”, “spars”, “ribs” and “pins” direct synaptic vesicle docking while “pins”, “ribs” and “pegs” regulate priming to influence Ca2+-triggering and membrane fusion. Other classes, “beams”, “steps”, “masts”, and “synaptic vesicle luminal filaments’ likely help organize and maintain the structural integrity of active zones. Extensive studies on the biochemistry that regulates secretion have led to comprehensive characterizations of the many conserved proteins universally involved in these trafficking events. Here, a hypothesis including a partial proteomic atlas of Active Zone Material is presented which considers the common roles, binding partners, physical features/structure, and relative positioning in the axon terminal of both the proteins and classes of macromolecules involved in the vesicle trafficking events. The hypothesis designates voltage-gated Ca2+ channels and Ca2+-gated K+ channels to ribs and pegs that are connected to macromolecules that span the presynaptic membrane at the active zone. SNARE proteins (Syntaxin, SNAP25, and Synaptobrevin), SNARE-interacting proteins Synaptotagmin, Munc13, Munc18, Complexin, and NSF are designated to ribs and/or pins. Rab3A and Rabphillin-3A are designated to top-masts and/or booms and/or spars. RIM, Bassoon, and Piccolo are designated to beams, steps, masts, ribs, spars, booms, and top-masts. Spectrin is designated to beams. Lastly, the luminal portions of SV2 are thought to form the bulk of the observed synaptic vesicle luminal filaments. The goal here is to help direct future studies that aim to bridge Active Zone Material structure, biochemistry, and function to ultimately determine how it regulates the trafficking events in vivo that lead to neurotransmitter secretion.
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25
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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.
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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
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26
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Bera M, Ramakrishnan S, Coleman J, Krishnakumar SS, Rothman JE. Molecular Determinants of Complexin Clamping in Reconstituted Single-Vesicle Fusion.. [DOI: 10.1101/2021.07.05.451112] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
ABSTRACTPreviously we reported that Synaptotagmin-1 and Complexin synergistically clamp the SNARE assembly process to generate and maintain a pool of docked vesicles that fuse rapidly and synchronously upon Ca2+ influx (Ramakrishnan et al. 2020). Here using the same in vitro single-vesicle fusion assay, we establish the molecular details of the Complexin clamp and its physiological relevance. We find that a delay in fusion kinetics, likely imparted by Synaptotagmin-1, is needed for Complexin to block fusion. Systematic truncation/mutational analyses reveal that continuous alpha-helical accessory-central domains of Complexin are essential for its inhibitory function and specific interaction of the accessory helix with the SNAREpins, analogous to the trans clamping model, enhances this functionality. The c-terminal domain promotes clamping by locally elevating Complexin concentration through interactions with the membrane. Further, we find that Complexin likely contributes to rapid Ca2+-synchronized vesicular release by preventing un-initiated fusion rather than by directly facilitating vesicle fusion.
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27
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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.
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28
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Bowman SL, Le L, Zhu Y, Harper DC, Sitaram A, Theos AC, Sviderskaya EV, Bennett DC, Raposo-Benedetti G, Owen DJ, Dennis MK, Marks MS. A BLOC-1-AP-3 super-complex sorts a cis-SNARE complex into endosome-derived tubular transport carriers. J Cell Biol 2021; 220:212016. [PMID: 33886957 PMCID: PMC8077166 DOI: 10.1083/jcb.202005173] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2020] [Revised: 02/15/2021] [Accepted: 03/19/2021] [Indexed: 02/02/2023] Open
Abstract
Membrane transport carriers fuse with target membranes through engagement of cognate vSNAREs and tSNAREs on each membrane. How vSNAREs are sorted into transport carriers is incompletely understood. Here we show that VAMP7, the vSNARE for fusing endosome-derived tubular transport carriers with maturing melanosomes in melanocytes, is sorted into transport carriers in complex with the tSNARE component STX13. Sorting requires either recognition of VAMP7 by the AP-3δ subunit of AP-3 or of STX13 by the pallidin subunit of BLOC-1, but not both. Consequently, melanocytes expressing both AP-3δ and pallidin variants that cannot bind their respective SNARE proteins are hypopigmented and fail to sort BLOC-1-dependent cargo, STX13, or VAMP7 into transport carriers. However, SNARE binding does not influence BLOC-1 function in generating tubular transport carriers. These data reveal a novel mechanism of vSNARE sorting by recognition of redundant sorting determinants on a SNARE complex by an AP-3-BLOC-1 super-complex.
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Affiliation(s)
- Shanna L. Bowman
- Department of Pathology & Laboratory Medicine, Children's Hospital of Philadelphia Research Institute, Philadelphia, PA,Department of Pathology & Laboratory Medicine, University of Pennsylvania, Philadelphia, PA,Department of Physiology, University of Pennsylvania, Philadelphia, PA,Department of Biology, Linfield University, McMinnville, OR
| | - Linh Le
- Department of Pathology & Laboratory Medicine, Children's Hospital of Philadelphia Research Institute, Philadelphia, PA,Department of Pathology & Laboratory Medicine, University of Pennsylvania, Philadelphia, PA,Department of Physiology, University of Pennsylvania, Philadelphia, PA,Cell and Molecular Biology Graduate Group, University of Pennsylvania, Philadelphia, PA
| | - Yueyao Zhu
- Department of Pathology & Laboratory Medicine, Children's Hospital of Philadelphia Research Institute, Philadelphia, PA,Department of Pathology & Laboratory Medicine, University of Pennsylvania, Philadelphia, PA,Department of Physiology, University of Pennsylvania, Philadelphia, PA,Department of Biology, University of Pennsylvania, Philadelphia, PA
| | - Dawn C. Harper
- Department of Pathology & Laboratory Medicine, Children's Hospital of Philadelphia Research Institute, Philadelphia, PA,Department of Pathology & Laboratory Medicine, University of Pennsylvania, Philadelphia, PA,Department of Physiology, University of Pennsylvania, Philadelphia, PA
| | - Anand Sitaram
- Department of Pathology & Laboratory Medicine, Children's Hospital of Philadelphia Research Institute, Philadelphia, PA,Department of Pathology & Laboratory Medicine, University of Pennsylvania, Philadelphia, PA,Department of Physiology, University of Pennsylvania, Philadelphia, PA
| | | | - Elena V. Sviderskaya
- Cell Biology Research Centre, Molecular and Clinical Sciences Research Institute, St George's, University of London, London, UK
| | - Dorothy C. Bennett
- Cell Biology Research Centre, Molecular and Clinical Sciences Research Institute, St George's, University of London, London, UK
| | - Graça Raposo-Benedetti
- Institut Curie, Paris Sciences et Lettres Research University, Centre National de la Recherche Scientifique Unité Mixte de Recherche 144, Compartiments de Structure et de Membrane, Paris, France
| | - David J. Owen
- Cambridge Institute for Medical Research, Cambridge, UK
| | - Megan K. Dennis
- Department of Pathology & Laboratory Medicine, Children's Hospital of Philadelphia Research Institute, Philadelphia, PA,Department of Pathology & Laboratory Medicine, University of Pennsylvania, Philadelphia, PA,Department of Physiology, University of Pennsylvania, Philadelphia, PA,Department of Biology, Marist College, Poughkeepsie, NY
| | - Michael S. Marks
- Department of Pathology & Laboratory Medicine, Children's Hospital of Philadelphia Research Institute, Philadelphia, PA,Department of Pathology & Laboratory Medicine, University of Pennsylvania, Philadelphia, PA,Department of Physiology, University of Pennsylvania, Philadelphia, PA,Correspondence to Michael S. Marks:
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29
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The Accessory Helix of Complexin Stabilizes a Partially Unzippered State of the SNARE Complex and Mediates the Complexin Clamping Function In Vivo. eNeuro 2021; 8:ENEURO.0526-20.2021. [PMID: 33692090 PMCID: PMC8026252 DOI: 10.1523/eneuro.0526-20.2021] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Revised: 01/16/2021] [Accepted: 02/09/2021] [Indexed: 12/17/2022] Open
Abstract
Spontaneous synaptic transmission is regulated by the protein complexin (Cpx). Cpx binds the SNARE complex, a coil-coiled four-helical bundle that mediates the attachment of a synaptic vesicle (SV) to the presynaptic membrane (PM). Cpx is thought to clamp spontaneous fusion events by stabilizing a partially unraveled state of the SNARE bundle; however, the molecular detail of this mechanism is still debated. We combined electrophysiology, molecular modeling, and site-directed mutagenesis in Drosophila to develop and validate the atomic model of the Cpx-mediated clamped state of the SNARE complex. We took advantage of botulinum neurotoxins (BoNTs) B and G, which cleave the SNARE protein synaptobrevin (Syb) at different sites. Monitoring synaptic depression on BoNT loading revealed that the clamped state of the SNARE complex has two or three unraveled helical turns of Syb. Site-directed mutagenesis showed that the Cpx clamping function is predominantly maintained by its accessory helix (AH), while molecular modeling suggested that the Cpx AH interacts with the unraveled C terminus of Syb and the SV lipid bilayer. The developed molecular model was employed to design new Cpx poor-clamp and super-clamp mutations and to tested the predictions in silico employing molecular dynamics simulations. Subsequently, we generated Drosophila lines harboring these mutations and confirmed the poor-clamp and super-clamp phenotypes in vivo. Altogether, these results validate the atomic model of the Cpx-mediated fusion clamp, wherein the Cpx AH inserts between the SNARE bundle and the SV lipid bilayer, simultaneously binding the unraveled C terminus of Syb and preventing full SNARE assembly.
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30
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Hirano AA, Vuong HE, Kornmann HL, Schietroma C, Stella SL, Barnes S, Brecha NC. Vesicular Release of GABA by Mammalian Horizontal Cells Mediates Inhibitory Output to Photoreceptors. Front Cell Neurosci 2020; 14:600777. [PMID: 33335476 PMCID: PMC7735995 DOI: 10.3389/fncel.2020.600777] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Accepted: 11/04/2020] [Indexed: 12/14/2022] Open
Abstract
Feedback inhibition by horizontal cells regulates rod and cone photoreceptor calcium channels that control their release of the neurotransmitter glutamate. This inhibition contributes to synaptic gain control and the formation of the center-surround antagonistic receptive fields passed on to all downstream neurons, which is important for contrast sensitivity and color opponency in vision. In contrast to the plasmalemmal GABA transporter found in non-mammalian horizontal cells, there is evidence that the mechanism by which mammalian horizontal cells inhibit photoreceptors involves the vesicular release of the inhibitory neurotransmitter GABA. Historically, inconsistent findings of GABA and its biosynthetic enzyme, L-glutamate decarboxylase (GAD) in horizontal cells, and the apparent lack of surround response block by GABAergic agents diminished support for GABA's role in feedback inhibition. However, the immunolocalization of the vesicular GABA transporter (VGAT) in the dendritic and axonal endings of horizontal cells that innervate photoreceptor terminals suggested GABA was released via vesicular exocytosis. To test the idea that GABA is released from vesicles, we localized GABA and GAD, multiple SNARE complex proteins, synaptic vesicle proteins, and Cav channels that mediate exocytosis to horizontal cell dendritic tips and axonal terminals. To address the perceived relative paucity of synaptic vesicles in horizontal cell endings, we used conical electron tomography on mouse and guinea pig retinas that revealed small, clear-core vesicles, along with a few clathrin-coated vesicles and endosomes in horizontal cell processes within photoreceptor terminals. Some small-diameter vesicles were adjacent to the plasma membrane and plasma membrane specializations. To assess vesicular release, a functional assay involving incubation of retinal slices in luminal VGAT-C antibodies demonstrated vesicles fused with the membrane in a depolarization- and calcium-dependent manner, and these labeled vesicles can fuse multiple times. Finally, targeted elimination of VGAT in horizontal cells resulted in a loss of tonic, autaptic GABA currents, and of inhibitory feedback modulation of the cone photoreceptor Cai, consistent with the elimination of GABA release from horizontal cell endings. These results in mammalian retina identify the central role of vesicular release of GABA from horizontal cells in the feedback inhibition of photoreceptors.
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Affiliation(s)
- Arlene A. Hirano
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Veterans Administration Greater Los Angeles Healthcare System, Los Angeles, CA, United States
| | - Helen E. Vuong
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - Helen L. Kornmann
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - Cataldo Schietroma
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - Salvatore L. Stella
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - Steven Barnes
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Department of Ophthalmology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Doheny Eye Institute, University of California, Los Angeles, Los Angeles, CA, United States
| | - Nicholas C. Brecha
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Veterans Administration Greater Los Angeles Healthcare System, Los Angeles, CA, United States
- Department of Ophthalmology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
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31
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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.
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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
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32
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Mu G, Xiang Q, Zhang Z, Liu C, Zhang H, Liu Z, Pang X, Jiang J, Xie Q, Zhou S, Wang Z, Hu K, Wang Z, Jiang S, Qin X, Cui Y. PNPT1 and PCGF3 variants associated with angiotensin-converting enzyme inhibitor-induced cough: a nested case–control genome-wide study. Pharmacogenomics 2020; 21:601-614. [PMID: 32397904 DOI: 10.2217/pgs-2019-0167] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Aim: We aimed to identify genetic variants associated with ACE inhibitor (ACEI)-induced cough. Materials & methods: A nested case–control study was performed among hypertensive Chinese patients receiving enalapril-only therapy. Whole-exome sequencing and genome-wide association analysis were performed. Results: We identified that PNPT1 rs13015243 (odds ratio [OR]: 0.47; 95% CI: 0.34–0.66; p = 7.45 × 10-6), PNPT1 rs13009649 (OR: 0.48; 95% CI: 0.35–0.67; p = 9.96 × 10-6) and PCGF3 rs1044147 (OR: 2.67; 95% CI: 1.71–4.17; p = 9.91 × 10-6) were significantly associated with ACEI-induced cough. Nearly genome-wide significant associations in previously reported candidate risk genes CLASP1, ACE, CES1, CPN1, XPNPEP1, PDE11A or SLC38A were detected in our dataset. Conclusion: Our results suggest that ACEI-induced cough is associated with noncoding SNPs of PNPT1 and PCGF3, all of which are independent of the bradykinin pathway. Study registration: NCT03259399.
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Affiliation(s)
- Guangyan Mu
- Department of Pharmacy, Peking University First Hospital, Beijing, 100034, China
| | - Qian Xiang
- Department of Pharmacy, Peking University First Hospital, Beijing, 100034, China
| | - Zhuo Zhang
- Department of Pharmacy, Peking University First Hospital, Beijing, 100034, China
| | - Chengzhang Liu
- Research Center, Shenzhen Evergreen Medical Institute, Shenzhen, 518057, China
| | - Hanxu Zhang
- Department of Pharmacy, Peking University First Hospital, Beijing, 100034, China
| | - Zhiyan Liu
- Department of Pharmacy, Peking University First Hospital, Beijing, 100034, China
| | - Xiaocong Pang
- Department of Pharmacy, Peking University First Hospital, Beijing, 100034, China
| | - Jie Jiang
- Department of Cardiology, Peking University First Hospital, Beijing, 100034, China
| | - Qiufen Xie
- Department of Pharmacy, Peking University First Hospital, Beijing, 100034, China
| | - Shuang Zhou
- Department of Pharmacy, Peking University First Hospital, Beijing, 100034, China
| | - Zining Wang
- Department of Pharmacy, Peking University First Hospital, Beijing, 100034, China
| | - Kun Hu
- Department of Pharmacy, Peking University First Hospital, Beijing, 100034, China
| | - Zhe Wang
- Department of Pharmacy, Peking University First Hospital, Beijing, 100034, China
| | - Shanqun Jiang
- School of Life Science, Anhui University, Hefei, 230601, China
| | - Xianhui Qin
- Division of Nephrology, Nanfang Hospital, Southern Medical University, Guangzhou, 510515, China
| | - Yimin Cui
- Department of Pharmacy, Peking University First Hospital, Beijing, 100034, China
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33
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Ramakrishnan S, Bera M, Coleman J, Rothman JE, Krishnakumar SS. Synergistic roles of Synaptotagmin-1 and complexin in calcium-regulated neuronal exocytosis. eLife 2020; 9:54506. [PMID: 32401194 PMCID: PMC7220375 DOI: 10.7554/elife.54506] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Accepted: 04/22/2020] [Indexed: 01/06/2023] Open
Abstract
Calcium (Ca2+)-evoked release of neurotransmitters from synaptic vesicles requires mechanisms both to prevent un-initiated fusion of vesicles (clamping) and to trigger fusion following Ca2+-influx. The principal components involved in these processes are the vesicular fusion machinery (SNARE proteins) and the regulatory proteins, Synaptotagmin-1 and Complexin. Here, we use a reconstituted single-vesicle fusion assay under physiologically-relevant conditions to delineate a novel mechanism by which Synaptotagmin-1 and Complexin act synergistically to establish Ca2+-regulated fusion. We find that under each vesicle, Synaptotagmin-1 oligomers bind and clamp a limited number of 'central' SNARE complexes via the primary interface and introduce a kinetic delay in vesicle fusion mediated by the excess of free SNAREpins. This in turn enables Complexin to arrest the remaining free 'peripheral' SNAREpins to produce a stably clamped vesicle. Activation of the central SNAREpins associated with Synaptotagmin-1 by Ca2+ is sufficient to trigger rapid (<100 msec) and synchronous fusion of the docked vesicles.
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Affiliation(s)
- Sathish Ramakrishnan
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States
| | - Manindra Bera
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States
| | - Jeff Coleman
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States
| | - James E Rothman
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States
| | - Shyam S Krishnakumar
- Department of Cell Biology, Yale University School of Medicine, New Haven, United States.,Department of Clinical and Experimental Epilepsy, Institute of Neurology, University College London, London, United Kingdom
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Yang L, Yang Y, Yuan J, Sun Y, Dai J, Su B. Transcriptomic Landscape of von Economo Neurons in Human Anterior Cingulate Cortex Revealed by Microdissected-Cell RNA Sequencing. Cereb Cortex 2020; 29:838-851. [PMID: 30535007 PMCID: PMC6319179 DOI: 10.1093/cercor/bhy286] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Indexed: 01/19/2023] Open
Abstract
The von Economo neurons (VENs) are specialized large bipolar projection neurons with restricted distribution in the human brain, and they are far more abundant in humans than in non-human primates. However, VEN functions remain elusive due to the difficulty of isolating VENs and dissecting their connections in the brain. Here, we combined laser-capture-microdissection with RNA sequencing to describe the transcriptomic profile of VENs from human anterior cingulate cortex (ACC). Using pyramidal neurons as reference cells, we identified 344 genes with VEN-associated expression differences, including 215 higher and 129 lower expression genes. Functional enrichment and protein–protein interaction network analyses showed that these genes with VEN-associated expression differences are involved in VEN morphogenesis and functions, such as dendrite branching and axon myelination, and many of them are associated with human social-emotional disorders. With the use of in situ hybridization and immunohistochemistry assays, we validated four novel VEN markers (VAT1L, CHST8, LYPD1, and SULF2). Collectively, we generated a full-spectrum expression profile of VENs from human ACC, greatly enlarging the pool of genes with VEN-associated expression differences that can help researchers to understand the role of VENs in normal and disordered human brains.
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Affiliation(s)
- Lixin Yang
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, China.,Center for Excellence in Animal Evolution and Genetics, Chinese Academy of Sciences, Kunming, China
| | - Yandong Yang
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, China.,Center for Excellence in Animal Evolution and Genetics, Chinese Academy of Sciences, Kunming, China.,Kunming College of Life Science, University of Chinese Academy of Sciences, Beijing, China
| | - Jiamiao Yuan
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, China.,Center for Excellence in Animal Evolution and Genetics, Chinese Academy of Sciences, Kunming, China.,Kunming College of Life Science, University of Chinese Academy of Sciences, Beijing, China
| | - Yan Sun
- Chinese Brain Bank Center, South-Central University for Nationalities, Wuhan, China
| | - Jiapei Dai
- Chinese Brain Bank Center, South-Central University for Nationalities, Wuhan, China
| | - Bing Su
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, China.,Center for Excellence in Animal Evolution and Genetics, Chinese Academy of Sciences, Kunming, China
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35
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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.
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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.
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36
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Wang S, Li Y, Gong J, Ye S, Yang X, Zhang R, Ma C. Munc18 and Munc13 serve as a functional template to orchestrate neuronal SNARE complex assembly. Nat Commun 2019; 10:69. [PMID: 30622273 PMCID: PMC6325239 DOI: 10.1038/s41467-018-08028-6] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2018] [Accepted: 12/12/2018] [Indexed: 11/30/2022] Open
Abstract
The transition of the Munc18-1/syntaxin-1 complex to the SNARE complex, a key step involved in exocytosis, is regulated by Munc13-1, SNAP-25 and synaptobrevin-2, but the underlying mechanism remains elusive. Here, we identify an interaction between Munc13-1 and the membrane-proximal linker region of synaptobrevin-2, and reveal its essential role in transition and exocytosis. Upon this interaction, Munc13-1 not only recruits synaptobrevin-2-embedded vesicles to the target membrane but also renders the synaptobrevin-2 SNARE motif more accessible to the Munc18-1/syntaxin-1 complex. Afterward, the entry of SNAP-25 leads to a half-zippered SNARE assembly, which eventually dissociates the Munc18-1/syntaxin-1 complex to complete SNARE complex formation. Our data suggest that Munc18-1 and Munc13-1 together serve as a functional template to orchestrate SNARE complex assembly. Synaptic exocytosis depends on formation of the SNARE complex but its assembly mechanism is still under debate. Here, the authors identify an interaction between Munc13-1 and synaptobrevin-2 that is critical for the transition of the Munc18-1/syntaxin-1 complex to the SNARE complex.
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Affiliation(s)
- Shen Wang
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, and the Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, 430074, Wuhan, China
| | - Yun Li
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, and the Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, 430074, Wuhan, China
| | - Jihong Gong
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, and the Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, 430074, Wuhan, China
| | - Sheng Ye
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 100101, Beijing, China
| | - Xiaofei Yang
- Key Laboratory of Cognitive Science, Hubei Key Laboratory of Medical Information Analysis and Tumor Diagnosis and Treatment, Laboratory of Membrane Ion Channels and Medicine, College of Biomedical Engineering, South-Central University for Nationalities, 430074, Wuhan, China
| | - Rongguang Zhang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 100101, Beijing, China.,National Center for Protein Science Shanghai, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Science, Chinese Academy of Sciences, 201203, Shanghai, China
| | - Cong Ma
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, and the Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, 430074, Wuhan, China.
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37
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Bykhovskaia M. Molecular Dynamics Simulations of the SNARE Complex. Methods Mol Biol 2018; 1860:3-13. [PMID: 30317495 DOI: 10.1007/978-1-4939-8760-3_1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/09/2023]
Abstract
Molecular dynamics (MD) simulations enable in silico investigations of the dynamic behavior of proteins and protein complexes. Here, we describe MD simulations of the SNARE complex and its interactions with the neuronal protein complexin. Complexin is an effector of neuronal secretion that inhibits spontaneous fusion and is thought to clamp the fusion process via the interactions with the SNARE complex. We describe MD simulations of the SNARE complex alone and bound to complexin. The MD simulations under external forces imitating the repulsion between lipid bilayers enabled us to investigate unraveling and assembly of the SNARE complex.
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Affiliation(s)
- Maria Bykhovskaia
- Department of Neurology, Wayne State University School of Medicine, Detroit, MI, USA. .,Department of Anatomy and Cell Biology, Wayne State University School of Medicine, Detroit, MI, USA.
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38
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SNAREpin Assembly: Kinetic and Thermodynamic Approaches. Methods Mol Biol 2018. [PMID: 30317499 DOI: 10.1007/978-1-4939-8760-3_5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Proteins constantly interact and often form molecular complexes. The dynamics of most biological processes strongly rely on the kinetics and thermodynamics of assembly and disassembly of these complexes. Consequently an accurate characterization of these kinetics and thermodynamics that underlie them provides key information to better understand these processes. Here, we present two efficient techniques to quantify the assembly and disassembly of protein complexes: isothermal titration calorimetry and fluorescence anisotropy. As an example we focus on the formation of SNAREpins and also present how to prepare SNARE proteins to use in these experimental setups. We then show how to use these techniques to determine the critical factors that activate assembly kinetics.
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39
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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.
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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.
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40
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Focused clamping of a single neuronal SNARE complex by complexin under high mechanical tension. Nat Commun 2018; 9:3639. [PMID: 30194295 PMCID: PMC6128827 DOI: 10.1038/s41467-018-06122-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2018] [Accepted: 08/14/2018] [Indexed: 01/10/2023] Open
Abstract
Neuronal soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) catalyze synaptic vesicle fusion with presynaptic membranes through the formation of SNARE complexes. Complexin (Cpx) is the only presynaptic protein that tightly binds to SNAREs and regulates membrane fusion, but how it modulates the energy landscape of SNARE complex assembly, especially under mechanical tension on the complex, remains unclear. Here, using magnetic tweezers, we report how Cpx interacts with single SNARE complexes. The effects of Cpx manifest only under high mechanical tensions above 13 pN. Cpx stabilizes the central four-helix bundle of SNARE motifs and, at the same time, prevents the complete zippering of SNAREs by inhibiting linker-domain assembly. These results suggest that Cpx generates a focused clamp for the neuronal SNARE complex in a linker-open conformation. Our results provide a hint as to how Cpx cooperates with neuronal SNAREs to prime synaptic vesicles in preparation for synchronous neurotransmitter release. The SNARE complex enables the fusion of synaptic vesicles with presynaptic membrane via a zippering process that is modulated by the protein complexin, though the precise mechanism remains unclear. Here, the authors used magnetic tweezers to show how complexin prepares a SNARE complex for fusion under mechanical tension.
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41
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Tam AB, Roberts LS, Chandra V, Rivera IG, Nomura DK, Forbes DJ, Niwa M. The UPR Activator ATF6 Responds to Proteotoxic and Lipotoxic Stress by Distinct Mechanisms. Dev Cell 2018; 46:327-343.e7. [PMID: 30086303 DOI: 10.1016/j.devcel.2018.04.023] [Citation(s) in RCA: 111] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2018] [Revised: 04/13/2018] [Accepted: 04/24/2018] [Indexed: 02/06/2023]
Abstract
The unfolded protein response (UPR) is induced by proteotoxic stress of the endoplasmic reticulum (ER). Here we report that ATF6, a major mammalian UPR sensor, is also activated by specific sphingolipids, dihydrosphingosine (DHS) and dihydroceramide (DHC). Single mutations in a previously undefined transmembrane domain motif that we identify in ATF6 incapacitate DHS/DHC activation while still allowing proteotoxic stress activation via the luminal domain. ATF6 thus possesses two activation mechanisms: DHS/DHC activation and proteotoxic stress activation. Reporters constructed to monitor each mechanism show that phenobarbital-induced ER membrane expansion depends on transmembrane domain-induced ATF6. DHS/DHC addition preferentially induces transcription of ATF6 target lipid biosynthetic and metabolic genes over target ER chaperone genes. Importantly, ATF6 containing a luminal achromatopsia eye disease mutation, unresponsive to proteotoxic stress, can be activated by fenretinide, a drug that upregulates DHC, suggesting a potential therapy for this and other ATF6-related diseases including heart disease and stroke.
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Affiliation(s)
- Arvin B Tam
- Division of Biological Sciences, Section of Molecular Biology, University of California, San Diego, NSB#1, Rm5328, 9500 Gilman Drive, La Jolla, CA 92093-0377, USA
| | - Lindsay S Roberts
- Department of Chemistry, Molecular and Cell Biology, and Nutritional Sciences and Toxicology, University of California, Berkeley, 127 Morgan Hall, Berkeley, CA 94720, USA
| | - Vivek Chandra
- Division of Biological Sciences, Section of Molecular Biology, University of California, San Diego, NSB#1, Rm5328, 9500 Gilman Drive, La Jolla, CA 92093-0377, USA
| | - Io Guane Rivera
- Division of Biological Sciences, Section of Molecular Biology, University of California, San Diego, NSB#1, Rm5328, 9500 Gilman Drive, La Jolla, CA 92093-0377, USA
| | - Daniel K Nomura
- Department of Chemistry, Molecular and Cell Biology, and Nutritional Sciences and Toxicology, University of California, Berkeley, 127 Morgan Hall, Berkeley, CA 94720, USA
| | - Douglass J Forbes
- Division of Biological Sciences, Section of Cell and Developmental Biology, University of California, San Diego, 2124A Pacific Hall, 9500 Gilman Drive, La Jolla, CA 92093-0347, USA
| | - Maho Niwa
- Division of Biological Sciences, Section of Molecular Biology, University of California, San Diego, NSB#1, Rm5328, 9500 Gilman Drive, La Jolla, CA 92093-0377, USA.
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42
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Brunger AT, Leitz J, Zhou Q, Choi UB, Lai Y. Ca 2+-Triggered Synaptic Vesicle Fusion Initiated by Release of Inhibition. Trends Cell Biol 2018; 28:631-645. [PMID: 29706534 PMCID: PMC6056330 DOI: 10.1016/j.tcb.2018.03.004] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Revised: 03/17/2018] [Accepted: 03/26/2018] [Indexed: 12/20/2022]
Abstract
Recent structural and functional studies of the synaptic vesicle fusion machinery suggest an inhibited tripartite complex consisting of neuronal soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs), synaptotagmin, and complexin prior to Ca2+-triggered synaptic vesicle fusion. We speculate that Ca2+-triggered fusion commences with the release of inhibition by Ca2+ binding to synaptotagmin C2 domains. Subsequently, fusion is assisted by SNARE complex zippering and by active membrane remodeling properties of synaptotagmin. This additional, inhibitory role of synaptotagmin may be a general principle since other recent studies suggest that Ca2+ binding to extended synaptotagmin C2 domains enables lipid transport by releasing an inhibited state of the system, and that Munc13 may nominally be in an inhibited state, which is released upon Ca2+ binding to one of its C2 domains.
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Affiliation(s)
- Axel T Brunger
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA; Department of Structural Biology, Stanford University, Stanford, CA, USA; Department of Photon Science, Stanford University, Stanford, CA, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA.
| | - Jeremy Leitz
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA; Department of Structural Biology, Stanford University, Stanford, CA, USA; Department of Photon Science, Stanford University, Stanford, CA, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA
| | - Qiangjun Zhou
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA; Department of Structural Biology, Stanford University, Stanford, CA, USA; Department of Photon Science, Stanford University, Stanford, CA, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA
| | - Ucheor B Choi
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA; Department of Structural Biology, Stanford University, Stanford, CA, USA; Department of Photon Science, Stanford University, Stanford, CA, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA
| | - Ying Lai
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA; Department of Structural Biology, Stanford University, Stanford, CA, USA; Department of Photon Science, Stanford University, Stanford, CA, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA
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43
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Synergistic control of neurotransmitter release by different members of the synaptotagmin family. Curr Opin Neurobiol 2018; 51:154-162. [DOI: 10.1016/j.conb.2018.05.006] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Revised: 05/19/2018] [Accepted: 05/21/2018] [Indexed: 01/06/2023]
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44
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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.
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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
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45
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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.
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Affiliation(s)
- Josep Rizo
- Departments of Biophysics, Biochemistry and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, 75390
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46
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Abstract
This review summarizes current knowledge of synaptic proteins that are central to synaptic vesicle fusion in presynaptic active zones, including SNAREs (soluble N-ethylmaleimide sensitive factor attachment protein receptors), synaptotagmin, complexin, Munc18 (mammalian uncoordinated-18), and Munc13 (mammalian uncoordinated-13), and highlights recent insights in the cooperation of these proteins for neurotransmitter release. Structural and functional studies of the synaptic fusion machinery suggest new molecular models of synaptic vesicle priming and Ca2+-triggered fusion. These studies will be a stepping-stone toward answering the question of how the synaptic vesicle fusion machinery achieves such high speed and sensitivity.
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Affiliation(s)
- Axel T Brunger
- Department of Molecular and Cellular Physiology, Department of Neurology and Neurological Sciences, Department of Structural Biology, Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA;
| | - Ucheor B Choi
- Department of Molecular and Cellular Physiology, Department of Neurology and Neurological Sciences, Department of Structural Biology, Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA;
| | - Ying Lai
- Department of Molecular and Cellular Physiology, Department of Neurology and Neurological Sciences, Department of Structural Biology, Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA;
| | - Jeremy Leitz
- Department of Molecular and Cellular Physiology, Department of Neurology and Neurological Sciences, Department of Structural Biology, Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA;
| | - Qiangjun Zhou
- Department of Molecular and Cellular Physiology, Department of Neurology and Neurological Sciences, Department of Structural Biology, Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA;
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47
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Rothman JE, Krishnakumar SS, Grushin K, Pincet F. Hypothesis - buttressed rings assemble, clamp, and release SNAREpins for synaptic transmission. FEBS Lett 2017; 591:3459-3480. [PMID: 28983915 PMCID: PMC5698743 DOI: 10.1002/1873-3468.12874] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Revised: 10/02/2017] [Accepted: 10/02/2017] [Indexed: 11/21/2022]
Abstract
Neural networks are optimized to detect temporal coincidence on the millisecond timescale. Here, we offer a synthetic hypothesis based on recent structural insights into SNAREs and the C2 domain proteins to explain how synaptic transmission can keep this pace. We suggest that an outer ring of up to six curved Munc13 ‘MUN’ domains transiently anchored to the plasma membrane via its flanking domains surrounds a stable inner ring comprised of synaptotagmin C2 domains to serve as a work‐bench on which SNAREpins are templated. This ‘buttressed‐ring hypothesis’ affords straightforward answers to many principal and long‐standing questions concerning how SNAREpins can be assembled, clamped, and then released synchronously with an action potential.
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Affiliation(s)
- James E Rothman
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - Shyam S Krishnakumar
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - Kirill Grushin
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - Frederic Pincet
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA.,Laboratoire de Physique Statistique, Ecole Normale Supérieure, PSL Research University, Université Paris Diderot Sorbonne Paris Cité, Sorbonne Universités UPMC Univ, CNRS, Paris, France
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48
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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.
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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.
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Prinslow EA, Brautigam CA, Rizo J. Reconciling isothermal titration calorimetry analyses of interactions between complexin and truncated SNARE complexes. eLife 2017; 6. [PMID: 28880148 PMCID: PMC5589412 DOI: 10.7554/elife.30286] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2017] [Accepted: 08/16/2017] [Indexed: 01/01/2023] Open
Abstract
Neurotransmitter release depends on the SNARE complex formed by syntaxin-1, synaptobrevin and SNAP-25, as well as on complexins, which bind to the SNARE complex and play active and inhibitory roles. A crystal structure of a Complexin-I fragment bearing a so-called 'superclamp' mutation bound to a truncated SNARE complex lacking the C-terminus of the synaptobrevin SNARE motif (SNAREΔ60) suggested that an 'accessory' α-helix of Complexin-I inhibits release by inserting into the C-terminus of the SNARE complex. Previously, isothermal titration calorimetry (ITC) experiments performed in different laboratories yielded apparently discrepant results in support or against the existence of such binding mode in solution (Trimbuch et al., 2014; Krishnakumar et al., 2015). Here, ITC experiments performed to solve these discrepancies now show that the region containing the Complexin-I accessory helix and preceding N-terminal sequences does interact with SNAREΔ60, but the interaction requires the polybasic juxtamembrane region of syntaxin-1 and is not affected by the superclamp mutation within the experimental error of these experiments.
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Affiliation(s)
- Eric A Prinslow
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Chad A Brautigam
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Josep Rizo
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
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50
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Gipson P, Fukuda Y, Danev R, Lai Y, Chen DH, Baumeister W, Brunger AT. Morphologies of synaptic protein membrane fusion interfaces. Proc Natl Acad Sci U S A 2017; 114:9110-9115. [PMID: 28739947 PMCID: PMC5576828 DOI: 10.1073/pnas.1708492114] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Neurotransmitter release is orchestrated by synaptic proteins, such as SNAREs, synaptotagmin, and complexin, but the molecular mechanisms remain unclear. We visualized functionally active synaptic proteins reconstituted into proteoliposomes and their interactions in a native membrane environment by electron cryotomography with a Volta phase plate for improved resolvability. The images revealed individual synaptic proteins and synaptic protein complex densities at prefusion contact sites between membranes. We observed distinct morphologies of individual synaptic proteins and their complexes. The minimal system, consisting of neuronal SNAREs and synaptotagmin-1, produced point and long-contact prefusion states. Morphologies and populations of these states changed as the regulatory factors complexin and Munc13 were added. Complexin increased the membrane separation, along with a higher propensity of point contacts. Further inclusion of the priming factor Munc13 exclusively restricted prefusion states to point contacts, all of which efficiently fused upon Ca2+ triggering. We conclude that synaptic proteins have evolved to limit possible contact site assemblies and morphologies to those that promote fast Ca2+-triggered release.
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Affiliation(s)
- Preeti Gipson
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305
- Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA 94305
- Department of Structural Biology, Stanford University, Stanford, CA 94305
- Department of Photon Science, Stanford University, Stanford, CA 94305
- Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305
| | - Yoshiyuki Fukuda
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Radostin Danev
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Ying Lai
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305
- Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA 94305
- Department of Structural Biology, Stanford University, Stanford, CA 94305
- Department of Photon Science, Stanford University, Stanford, CA 94305
- Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305
| | - Dong-Hua Chen
- Department of Structural Biology, Stanford University, Stanford, CA 94305
| | - Wolfgang Baumeister
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Axel T Brunger
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305;
- Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA 94305
- Department of Structural Biology, Stanford University, Stanford, CA 94305
- Department of Photon Science, Stanford University, Stanford, CA 94305
- Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305
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