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Leitz J, Wang C, Esquivies L, Pfuetzner RA, Peters JJ, Couoh-Cardel S, Wang AL, Brunger AT. Beyond the MUN domain, Munc13 controls priming and depriming of synaptic vesicles. Cell Rep 2024; 43:114026. [PMID: 38809756 PMCID: PMC11286359 DOI: 10.1016/j.celrep.2024.114026] [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: 11/20/2023] [Revised: 02/20/2024] [Accepted: 03/15/2024] [Indexed: 05/31/2024] Open
Abstract
Synaptic vesicle docking and priming are dynamic processes. At the molecular level, SNAREs (soluble NSF attachment protein receptors), synaptotagmins, and other factors are critical for Ca2+-triggered vesicle exocytosis, while disassembly factors, including NSF (N-ethylmaleimide-sensitive factor) and α-SNAP (soluble NSF attachment protein), disassemble and recycle SNAREs and antagonize fusion under some conditions. Here, we introduce a hybrid fusion assay that uses synaptic vesicles isolated from mouse brains and synthetic plasma membrane mimics. We included Munc18, Munc13, complexin, NSF, α-SNAP, and an ATP-regeneration system and maintained them continuously-as in the neuron-to investigate how these opposing processes yield fusogenic synaptic vesicles. In this setting, synaptic vesicle association is reversible, and the ATP-regeneration system produces the most synchronous Ca2+-triggered fusion, suggesting that disassembly factors perform quality control at the early stages of synaptic vesicle association to establish a highly fusogenic state. We uncovered a functional role for Munc13 ancillary to the MUN domain that alleviates an α-SNAP-dependent inhibition of Ca2+-triggered fusion.
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Affiliation(s)
- 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
| | - Chuchu Wang
- 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
| | - Luis Esquivies
- 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
| | - Richard A Pfuetzner
- 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
| | - John Jacob Peters
- 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
| | - Sergio Couoh-Cardel
- 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
| | - Austin L Wang
- 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
| | - 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.
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2
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Bhaskar BR, Yadav L, Sriram M, Sanghrajka K, Gupta M, V BK, Nellikka RK, Das D. Differential SNARE chaperoning by Munc13-1 and Munc18-1 dictates fusion pore fate at the release site. Nat Commun 2024; 15:4132. [PMID: 38755165 PMCID: PMC11099066 DOI: 10.1038/s41467-024-46965-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Accepted: 03/14/2024] [Indexed: 05/18/2024] Open
Abstract
The regulated release of chemical messengers is crucial for cell-to-cell communication; abnormalities in which impact coordinated human body function. During vesicular secretion, multiple SNARE complexes assemble at the release site, leading to fusion pore opening. How membrane fusion regulators act on heterogeneous SNARE populations to assemble fusion pores in a timely and synchronized manner, is unknown. Here, we demonstrate the role of SNARE chaperones Munc13-1 and Munc18-1 in rescuing individual nascent fusion pores from their diacylglycerol lipid-mediated inhibitory states. At the onset of membrane fusion, Munc13-1 clusters multiple SNARE complexes at the release site and synchronizes release events, while Munc18-1 stoichiometrically interacts with trans-SNARE complexes to enhance N- to C-terminal zippering. When both Munc proteins are present simultaneously, they differentially access dynamic trans-SNARE complexes to regulate pore properties. Overall, Munc proteins' direct action on fusion pore assembly indicates their role in controlling quantal size during vesicular secretion.
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Affiliation(s)
- Bhavya R Bhaskar
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Laxmi Yadav
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Malavika Sriram
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Kinjal Sanghrajka
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Mayank Gupta
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Boby K V
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Rohith K Nellikka
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Debasis Das
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India.
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3
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Kádková A, Murach J, Østergaard M, Malsam A, Malsam J, Lolicato F, Nickel W, Söllner TH, Sørensen JB. SNAP25 disease mutations change the energy landscape for synaptic exocytosis due to aberrant SNARE interactions. eLife 2024; 12:RP88619. [PMID: 38411501 PMCID: PMC10911398 DOI: 10.7554/elife.88619] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/28/2024] Open
Abstract
SNAP25 is one of three neuronal SNAREs driving synaptic vesicle exocytosis. We studied three mutations in SNAP25 that cause epileptic encephalopathy: V48F, and D166Y in the synaptotagmin-1 (Syt1)-binding interface, and I67N, which destabilizes the SNARE complex. All three mutations reduced Syt1-dependent vesicle docking to SNARE-carrying liposomes and Ca2+-stimulated membrane fusion in vitro and when expressed in mouse hippocampal neurons. The V48F and D166Y mutants (with potency D166Y > V48F) led to reduced readily releasable pool (RRP) size, due to increased spontaneous (miniature Excitatory Postsynaptic Current, mEPSC) release and decreased priming rates. These mutations lowered the energy barrier for fusion and increased the release probability, which are gain-of-function features not found in Syt1 knockout (KO) neurons; normalized mEPSC release rates were higher (potency D166Y > V48F) than in the Syt1 KO. These mutations (potency D166Y > V48F) increased spontaneous association to partner SNAREs, resulting in unregulated membrane fusion. In contrast, the I67N mutant decreased mEPSC frequency and evoked EPSC amplitudes due to an increase in the height of the energy barrier for fusion, whereas the RRP size was unaffected. This could be partly compensated by positive charges lowering the energy barrier. Overall, pathogenic mutations in SNAP25 cause complex changes in the energy landscape for priming and fusion.
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Affiliation(s)
- Anna Kádková
- Department of Neuroscience, University of CopenhagenCopenhagenDenmark
| | | | - Maiken Østergaard
- Department of Neuroscience, University of CopenhagenCopenhagenDenmark
| | - Andrea Malsam
- Heidelberg University Biochemistry CenterHeidelbergDenmark
| | - Jörg Malsam
- Heidelberg University Biochemistry CenterHeidelbergDenmark
| | - Fabio Lolicato
- Heidelberg University Biochemistry CenterHeidelbergDenmark
- Department of Physics, University of HelsinkiHelsinkiFinland
| | - Walter Nickel
- Heidelberg University Biochemistry CenterHeidelbergDenmark
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4
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Hong S, Yang T, Go A, Kim H, Yoon TY, Shon MJ. High-speed measurements of SNARE-complexin interactions using magnetic tweezers. Methods Enzymol 2024; 694:109-135. [PMID: 38492948 DOI: 10.1016/bs.mie.2024.01.002] [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] [Indexed: 03/18/2024]
Abstract
In neuroscience, understanding the mechanics of synapses, especially the function of force-sensitive proteins at the molecular level, is essential. This need emphasizes the importance of precise measurement of synaptic protein interactions. Addressing this, we introduce high-resolution magnetic tweezers (MT) as a novel method to probe the mechanics of synapse-related proteins with high precision. We demonstrate this technique through studying SNARE-complexin interactions, crucial for synaptic transmission, showcasing its capability to apply specific forces to individual molecules. Our results reveal that high-resolution MT provides in-depth insights into the stability and dynamic transitions of synaptic protein complexes. This method is a significant advancement in synapse biology, offering a new tool for researchers to investigate the impact of mechanical forces on synaptic functions and their implications for neurological disorders.
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Affiliation(s)
- Seokyun Hong
- Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
| | - Taehyun Yang
- Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
| | - Ara Go
- Engitein Research Institute, Engitein, Siheung, Republic of Korea
| | - Haesoo Kim
- Engitein Research Institute, Engitein, Siheung, Republic of Korea
| | - Tae-Young Yoon
- School of Biological Sciences and Institute for Molecular Biology and Genetics, Seoul National University, Seoul, Republic of Korea; Department of Biomarker Discovery, PROTEINA Co., Ltd, Seoul, Republic of Korea.
| | - Min Ju Shon
- Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea; School of Interdisciplinary Bioscience and Bioengineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea.
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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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Li F, Grushin K, Coleman J, Pincet F, Rothman JE. Diacylglycerol-dependent hexamers of the SNARE-assembling chaperone Munc13-1 cooperatively bind vesicles. Proc Natl Acad Sci U S A 2023; 120:e2306086120. [PMID: 37883433 PMCID: PMC10623011 DOI: 10.1073/pnas.2306086120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Accepted: 09/28/2023] [Indexed: 10/28/2023] Open
Abstract
Munc13-1 is essential for vesicle docking and fusion at the active zone of synapses. Here, we report that Munc13-1 self-assembles into molecular clusters within diacylglycerol-rich microdomains present in phospholipid bilayers. Although the copy number of Munc13-1 molecules in these clusters has a broad distribution, a systematic Poisson analysis shows that this is most likely the result of two molecular species: monomers and mainly hexameric oligomers. Each oligomer is able to capture one vesicle independently. Hexamers have also been observed in crystals of Munc13-1 that form between opposed phospholipid bilayers [K. Grushin, R. V. Kalyana Sundaram, C. V. Sindelar, J. E. Rothman, Proc. Natl. Acad. Sci. U.S.A. 119, e2121259119 (2022)]. Mutations targeting the contacts stabilizing the crystallographic hexagons also disrupt the isolated hexamers, suggesting they are identical. Additionally, these mutations also convert vesicle binding from a cooperative to progressive mode. Our study provides an independent approach showing that Munc13-1 can form mainly hexamers on lipid bilayers each capable of vesicle capture.
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Affiliation(s)
- Feng Li
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT06520
- Nanobiology Institute, School of Medicine, Yale University, West Haven, CT06516
| | - Kirill Grushin
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT06520
- Nanobiology Institute, School of Medicine, Yale University, West Haven, CT06516
| | - Jeff Coleman
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT06520
- Nanobiology Institute, School of Medicine, Yale University, West Haven, CT06516
| | - Frederic Pincet
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT06520
- Nanobiology Institute, School of Medicine, Yale University, West Haven, CT06516
- Laboratoire de Physique de l’Ecole normale supérieure, Département de Physique, Ecole Normale Supérieure, Université Paris Sciences & Lettres CNRS, Sorbonne Université, Université de Paris, ParisF-75005, France
| | - James E. Rothman
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT06520
- Nanobiology Institute, School of Medicine, Yale University, West Haven, CT06516
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7
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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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8
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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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9
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Bera M, Grushin K, Sundaram RVK, Shahanoor Z, Chatterjee A, Radhakrishnan A, Lee S, Padmanarayana M, Coleman J, Pincet F, Rothman JE, Dittman JS. Two successive oligomeric Munc13 assemblies scaffold vesicle docking and SNARE assembly to support neurotransmitter release. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.14.549017. [PMID: 37503179 PMCID: PMC10369971 DOI: 10.1101/2023.07.14.549017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/29/2023]
Abstract
The critical presynaptic protein Munc13 serves numerous roles in the process of docking and priming synaptic vesicles. Here we investigate the functional significance of two distinct oligomers of the Munc13 core domain (Munc13C) comprising C1-C2B-MUN-C2C. Oligomer interface point mutations that specifically destabilized either the trimer or lateral hexamer assemblies of Munc13C disrupted vesicle docking, trans-SNARE formation, and Ca 2+ -triggered vesicle fusion in vitro and impaired neurotransmitter secretion and motor nervous system function in vivo. We suggest that a progression of oligomeric Munc13 complexes couples vesicle docking and assembly of a precise number of SNARE molecules to support rapid and high-fidelity vesicle priming.
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10
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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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11
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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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12
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Palfreyman MT, West SE, Jorgensen EM. SNARE Proteins in Synaptic Vesicle Fusion. ADVANCES IN NEUROBIOLOGY 2023; 33:63-118. [PMID: 37615864 DOI: 10.1007/978-3-031-34229-5_4] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Abstract
Neurotransmitters are stored in small membrane-bound vesicles at synapses; a subset of synaptic vesicles is docked at release sites. Fusion of docked vesicles with the plasma membrane releases neurotransmitters. Membrane fusion at synapses, as well as all trafficking steps of the secretory pathway, is mediated by SNARE proteins. The SNAREs are the minimal fusion machinery. They zipper from N-termini to membrane-anchored C-termini to form a 4-helix bundle that forces the apposed membranes to fuse. At synapses, the SNAREs comprise a single helix from syntaxin and synaptobrevin; SNAP-25 contributes the other two helices to complete the bundle. Unc13 mediates synaptic vesicle docking and converts syntaxin into the permissive "open" configuration. The SM protein, Unc18, is required to initiate and proofread SNARE assembly. The SNAREs are then held in a half-zippered state by synaptotagmin and complexin. Calcium removes the synaptotagmin and complexin block, and the SNAREs drive vesicle fusion. After fusion, NSF and alpha-SNAP unwind the SNAREs and thereby recharge the system for further rounds of fusion. In this chapter, we will describe the discovery of the SNAREs, their relevant structural features, models for their function, and the central role of Unc18. In addition, we will touch upon the regulation of SNARE complex formation by Unc13, complexin, and synaptotagmin.
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Affiliation(s)
- Mark T Palfreyman
- School of Biological Sciences, and Howard Hughes Medical Institute, University of Utah, Salt Lake City, UT, USA
| | - Sam E West
- School of Biological Sciences, and Howard Hughes Medical Institute, University of Utah, Salt Lake City, UT, USA
| | - Erik M Jorgensen
- School of Biological Sciences, and Howard Hughes Medical Institute, University of Utah, Salt Lake City, UT, USA.
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13
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Kalyana Sundaram RV, Bera M, Coleman J, Weerakkody JS, Krishnakumar SS, Ramakrishnan S. Native Planar Asymmetric Suspended Membrane for Single-Molecule Investigations: Plasma Membrane on a Chip. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2022; 18:e2205567. [PMID: 36328714 DOI: 10.1002/smll.202205567] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Indexed: 06/16/2023]
Abstract
Cellular plasma membranes, in their role as gatekeepers to the external environment, host numerous protein assemblies and lipid domains that manage the movement of molecules into and out of cells, regulate electric potential, and direct cell signaling. The ability to investigate these roles on the bilayer at a single-molecule level in a controlled, in vitro environment while preserving lipid and protein architectures will provide deeper insights into how the plasma membrane works. A tunable silicon microarray platform that supports stable, planar, and asymmetric suspended lipid membranes (SLIM) using synthetic and native plasma membrane vesicles for single-molecule fluorescence investigations is developed. Essentially, a "plasma membrane-on-a-chip" system that preserves lipid asymmetry and protein orientation is created. By harnessing the combined potential of this platform with total internal reflection fluorescence (TIRF) microscopy, the authors are able to visualize protein complexes with single-molecule precision. This technology has widespread applications in biological processes that happen at the cellular membranes and will further the knowledge of lipid and protein assemblies.
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Affiliation(s)
- Ramalingam Venkat Kalyana Sundaram
- Nanobiology Institute, Yale University School of Medicine, West Haven, CT, 06516, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, 06520, USA
| | - Manindra Bera
- Nanobiology Institute, Yale University School of Medicine, West Haven, CT, 06516, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, 06520, USA
| | - Jeff Coleman
- Nanobiology Institute, Yale University School of Medicine, West Haven, CT, 06516, USA
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, 06520, USA
| | - Jonathan S Weerakkody
- Nanobiology Institute, Yale University School of Medicine, West Haven, CT, 06516, USA
- Department of Pathology, Yale University School of Medicine, New Haven, CT, 06520, USA
| | - Shyam S Krishnakumar
- Nanobiology Institute, Yale University School of Medicine, West Haven, CT, 06516, USA
- Department of Neurology, Yale University School of Medicine, New Haven, CT, 06520, USA
| | - Sathish Ramakrishnan
- Nanobiology Institute, Yale University School of Medicine, West Haven, CT, 06516, USA
- Department of Pathology, Yale University School of Medicine, New Haven, CT, 06520, USA
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14
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Li T, Cheng Q, Wang S, Ma C. Rabphilin 3A binds the N-peptide of SNAP-25 to promote SNARE complex assembly in exocytosis. eLife 2022; 11:79926. [PMID: 36173100 PMCID: PMC9522249 DOI: 10.7554/elife.79926] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2022] [Accepted: 09/13/2022] [Indexed: 11/13/2022] Open
Abstract
Exocytosis of secretory vesicles requires the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins and small GTPase Rabs. As a Rab3/Rab27 effector protein on secretory vesicles, Rabphilin 3A was implicated to interact with SNAP-25 to regulate vesicle exocytosis in neurons and neuroendocrine cells, yet the underlying mechanism remains unclear. In this study, we have characterized the physiologically relevant binding sites between Rabphilin 3A and SNAP-25. We found that an intramolecular interplay between the N-terminal Rab-binding domain and C-terminal C2AB domain enables Rabphilin 3A to strongly bind the SNAP-25 N-peptide region via its C2B bottom α-helix. Disruption of this interaction significantly impaired docking and fusion of vesicles with the plasma membrane in rat PC12 cells. In addition, we found that this interaction allows Rabphilin 3A to accelerate SNARE complex assembly. Furthermore, we revealed that this interaction accelerates SNARE complex assembly via inducing a conformational switch from random coils to α-helical structure in the SNAP-25 SNARE motif. Altogether, our data suggest that the promotion of SNARE complex assembly by binding the C2B bottom α-helix of Rabphilin 3A to the N-peptide of SNAP-25 underlies a pre-fusion function of Rabphilin 3A in vesicle exocytosis.
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Affiliation(s)
- Tianzhi Li
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Qiqi Cheng
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - 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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15
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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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16
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Zhang Y, Ma L, Bao H. Energetics, kinetics, and pathways of SNARE assembly in membrane fusion. Crit Rev Biochem Mol Biol 2022; 57:443-460. [PMID: 36151854 PMCID: PMC9588726 DOI: 10.1080/10409238.2022.2121804] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Fusion of transmitter-containing vesicles with plasma membranes at the synaptic and neuromuscular junctions mediates neurotransmission and muscle contractions, respectively, thereby underlying all thoughts and actions. The fusion process is driven by the coupled folding and assembly of three synaptic SNARE proteins--syntaxin-1 and SNAP-25 on the target plasma membrane (t-SNAREs) and VAMP2 on the vesicular membrane (v-SNARE) into a four-helix bundle. Their assembly is chaperoned by Munc18-1 and many other proteins to achieve the speed and accuracy required for neurotransmission. However, the physiological pathway of SNARE assembly and its coupling to membrane fusion remains unclear. Here, we review recent progress in understanding SNARE assembly and membrane fusion, with a focus on results obtained by single-molecule manipulation approaches and electric recordings of single fusion pores. We describe two pathways of synaptic SNARE assembly, their associated intermediates, energetics, and kinetics. Assembly of the three SNAREs in vitro begins with the formation of a t-SNARE binary complex, on which VAMP2 folds in a stepwise zipper-like fashion. Munc18-1 significantly alters the SNARE assembly pathway: syntaxin-1 and VAMP2 first bind on the surface of Munc18-1 to form a template complex, with which SNAP-25 associates to conclude SNARE assembly and displace Munc18-1. During membrane fusion, multiple trans-SNARE complexes cooperate to open a dynamic fusion pore in a manner dependent upon their copy number and zippering states. Together, these results demonstrate that stepwise and cooperative SNARE assembly drive stagewise membrane fusion.
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Affiliation(s)
- Yongli Zhang
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA;,Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06511, USA;,Conatct: and
| | - Lu Ma
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA;,Present address: Beijing National Laboratory for Condensed Matter Physics and CAS Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Huan Bao
- Department of Molecular Medicine, The Scripps Research Institute, 130 Scripps Way, Jupiter, Florida, 33458,Conatct: and
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17
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Parra-Rivas LA, Palfreyman MT, Vu TN, Jorgensen EM. Interspecies complementation identifies a pathway to assemble SNAREs. iScience 2022; 25:104506. [PMID: 35754735 PMCID: PMC9213704 DOI: 10.1016/j.isci.2022.104506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2021] [Revised: 03/23/2022] [Accepted: 05/27/2022] [Indexed: 11/18/2022] Open
Abstract
Unc18 and SNARE proteins form the core of the membrane fusion complex at synapses. To understand the functional interactions within the core machinery, we adopted an "interspecies complementation" approach in Caenorhabditis elegans. Substitutions of individual SNAREs and Unc18 proteins with those from yeast fail to rescue fusion. However, synaptic transmission could be restored in worm-yeast chimeras when two key interfaces were present: an Habc-Unc18 contact site and an Unc18-SNARE motif contact site. A constitutively open form of Unc18 bypasses the requirement for the Habc-Unc18 interface. These data suggest that the Habc domain of syntaxin is required for Unc18 to adopt an open conformation; open Unc18 then templates SNARE complex formation. Finally, we demonstrate that the SNARE and Unc18 machinery in the nematode C. elegans can be replaced by yeast proteins and still carry out synaptic transmission, pointing to the deep evolutionary conservation of these two interfaces.
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Affiliation(s)
- Leonardo A. Parra-Rivas
- Howard Hughes Medical Institute, School of Biological Sciences, University of Utah, Salt Lake City, UT 84112-0840, USA
| | - Mark T. Palfreyman
- Howard Hughes Medical Institute, School of Biological Sciences, University of Utah, Salt Lake City, UT 84112-0840, USA
| | - Thien N. Vu
- Howard Hughes Medical Institute, School of Biological Sciences, University of Utah, Salt Lake City, UT 84112-0840, USA
| | - Erik M. Jorgensen
- Howard Hughes Medical Institute, School of Biological Sciences, University of Utah, Salt Lake City, UT 84112-0840, USA
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18
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Mion D, Bunel L, Heo P, Pincet F. The beginning and the end of SNARE-induced membrane fusion. FEBS Open Bio 2022; 12:1958-1979. [PMID: 35622519 PMCID: PMC9623537 DOI: 10.1002/2211-5463.13447] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 05/11/2022] [Accepted: 05/25/2022] [Indexed: 01/25/2023] Open
Abstract
Membrane fusion is not a spontaneous process. Physiologically, the formation of coiled-coil protein complexes, the SNAREpins, bridges the membrane of a vesicle and a target membrane, brings them in close contact, and provides the energy necessary for their fusion. In this review, we utilize results from in vitro experiments and simple physics and chemistry models to dissect the kinetics and energetics of the fusion process from the encounter of the two membranes to the full expansion of a fusion pore. We find three main energy barriers that oppose the fusion process: SNAREpin initiation, fusion pore opening, and expansion. SNAREpin initiation is inherent to the proteins and makes in vitro fusion kinetic experiments rather slow. The kinetics are physiologically accelerated by effectors. The energy barriers that precede pore opening and pore expansion can be overcome by several SNAREpins acting in concert.
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Affiliation(s)
- Delphine Mion
- Laboratoire de Physique de l'École Normale Supérieure, ENS, Université PSLCNRS, Sorbonne Université, Université Paris CitéFrance
| | - Louis Bunel
- Laboratoire de Physique de l'École Normale Supérieure, ENS, Université PSLCNRS, Sorbonne Université, Université Paris CitéFrance
| | - Paul Heo
- Institute of Psychiatry and Neuroscience of Paris (IPNP)INSERM U1266ParisFrance
| | - Frédéric Pincet
- Laboratoire de Physique de l'École Normale Supérieure, ENS, Université PSLCNRS, Sorbonne Université, Université Paris CitéFrance
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19
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Xu Y, Zhu L, Wang S, Ma C. Munc18 − Munc13‐dependent pathway of
SNARE
complex assembly is resistant to
NSF
and
α‐SNAP. FEBS J 2022; 289:6367-6384. [DOI: 10.1111/febs.16528] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Revised: 04/26/2022] [Accepted: 05/12/2022] [Indexed: 11/28/2022]
Affiliation(s)
- Yuanyuan Xu
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology Huazhong University of Science and Technology Wuhan China
| | - Le Zhu
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology Huazhong University of Science and Technology Wuhan China
| | - 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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20
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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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21
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Wang S, Ma C. Neuronal SNARE complex assembly guided by Munc18-1 and Munc13-1. FEBS Open Bio 2022; 12:1939-1957. [PMID: 35278279 PMCID: PMC9623535 DOI: 10.1002/2211-5463.13394] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2022] [Revised: 02/28/2022] [Accepted: 03/10/2022] [Indexed: 01/25/2023] Open
Abstract
Neurotransmitter release by Ca2+ -triggered synaptic vesicle exocytosis is essential for information transmission in the nervous system. The soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs) syntaxin-1, SNAP-25, and synaptobrevin-2 form the SNARE complex to bring synaptic vesicles and the plasma membranes together and to catalyze membrane fusion. Munc18-1 and Munc13-1 regulate synaptic vesicle priming via orchestrating neuronal SNARE complex assembly. In this review, we summarize recent advances toward the functions and molecular mechanisms of Munc18-1 and Munc13-1 in guiding neuronal SNARE complex assembly, and discuss the functional similarities and differences between Munc18-1 and Munc13-1 in neurons and their homologs in other intracellular membrane trafficking systems.
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Affiliation(s)
- Shen Wang
- Key Laboratory of Molecular Biophysics of the Ministry of EducationCollege of Life Science and TechnologyHuazhong University of Science and TechnologyWuhanChina
| | - Cong Ma
- Key Laboratory of Molecular Biophysics of the Ministry of EducationCollege of Life Science and TechnologyHuazhong University of Science and TechnologyWuhanChina
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22
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Munc13 structural transitions and oligomers that may choreograph successive stages in vesicle priming for neurotransmitter release. Proc Natl Acad Sci U S A 2022; 119:2121259119. [PMID: 35135883 PMCID: PMC8851502 DOI: 10.1073/pnas.2121259119] [Citation(s) in RCA: 30] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/21/2021] [Indexed: 12/24/2022] Open
Abstract
The speed of neural information processing in the human central nervous system is ultimately determined by the speed of chemical transmission at synapses, because action potentials have relatively short distances to traverse. The release of synaptic vesicles containing neurotransmitters must therefore be remarkably fast as compared to other forms of membrane fusion. Six separate SNARE complexes cooperate to achieve this. But how can exactly six copies be assembled under every vesicle? Here we report that six copies of the key molecular chaperone that assembles the SNAREs can arrange themselves into a closed hexagon, providing the likely answer. How can exactly six SNARE complexes be assembled under each synaptic vesicle? Here we report cryo-EM crystal structures of the core domain of Munc13, the key chaperone that initiates SNAREpin assembly. The functional core of Munc13, consisting of C1–C2B–MUN–C2C (Munc13C) spontaneously crystallizes between phosphatidylserine-rich bilayers in two distinct conformations, each in a radically different oligomeric state. In the open conformation (state 1), Munc13C forms upright trimers that link the two bilayers, separating them by ∼21 nm. In the closed conformation, six copies of Munc13C interact to form a lateral hexamer elevated ∼14 nm above the bilayer. Open and closed conformations differ only by a rigid body rotation around a flexible hinge, which when performed cooperatively assembles Munc13 into a lateral hexamer (state 2) in which the key SNARE assembly-activating site of Munc13 is autoinhibited by its neighbor. We propose that each Munc13 in the lateral hexamer ultimately assembles a single SNAREpin, explaining how only and exactly six SNARE complexes are templated. We suggest that state 1 and state 2 may represent two successive states in the synaptic vesicle supply chain leading to “primed” ready-release vesicles in which SNAREpins are clamped and ready to release (state 3).
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23
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Yang T, Park C, Rah SH, Shon MJ. Nano-Precision Tweezers for Mechanosensitive Proteins and Beyond. Mol Cells 2022; 45:16-25. [PMID: 35114644 PMCID: PMC8819490 DOI: 10.14348/molcells.2022.2026] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2021] [Revised: 01/10/2022] [Accepted: 01/12/2022] [Indexed: 11/27/2022] Open
Abstract
Mechanical forces play pivotal roles in regulating cell shape, function, and fate. Key players that govern the mechanobiological interplay are the mechanosensitive proteins found on cell membranes and in cytoskeleton. Their unique nanomechanics can be interrogated using single-molecule tweezers, which can apply controlled forces to the proteins and simultaneously measure the ensuing structural changes. Breakthroughs in high-resolution tweezers have enabled the routine monitoring of nanometer-scale, millisecond dynamics as a function of force. Undoubtedly, the advancement of structural biology will be further fueled by integrating static atomic-resolution structures and their dynamic changes and interactions observed with the force application techniques. In this minireview, we will introduce the general principles of single-molecule tweezers and their recent applications to the studies of force-bearing proteins, including the synaptic proteins that need to be categorized as mechanosensitive in a broad sense. We anticipate that the impact of nano-precision approaches in mechanobiology research will continue to grow in the future.
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Affiliation(s)
- Taehyun Yang
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Celine Park
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Sang-Hyun Rah
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Min Ju Shon
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
- School of Interdisciplinary Bioscience and Bioengineering, Pohang University of Science and Technology, Pohang 37673, Korea
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Gong J, Wang X, Cui C, Qin Y, Jin Z, Ma C, Yang X. Exploring the Two Coupled Conformational Changes That Activate the Munc18-1/Syntaxin-1 Complex. Front Mol Neurosci 2022; 14:785696. [PMID: 35002621 PMCID: PMC8728020 DOI: 10.3389/fnmol.2021.785696] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2021] [Accepted: 11/26/2021] [Indexed: 11/17/2022] Open
Abstract
Calcium-dependent synaptic vesicle exocytosis is mediated by SNARE complex formation. The transition from the Munc18-1/syntaxin-1 complex to the SNARE complex is catalyzed by the Munc13-1 MUN domain and involves at least two conformational changes: opening of the syntaxin-1 linker region and extension of Munc18-1 domain 3a. However, the relationship and the action order of the two conformational changes remain not fully understood. Here, our data show that an open conformation in the syntaxin-1 linker region can bypass the requirement of the MUN NF sequence. In addition, an extended state of Munc18-1 domain 3a can compensate the role of the syntaxin-1 RI sequence. Altogether, the current data strongly support our previous notion that opening of the syntaxin-1 linker region by Munc13-1 is a key step to initiate SNARE complex assembly, and consequently, Munc18-1 domain 3a can extend its conformation to serve as a template for association of synaptobrevin-2 and syntaxin-1.
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Affiliation(s)
- Jihong Gong
- Key Laboratory of Cognitive Science, Laboratory of Membrane Ion Channels and Medicine, College of Biomedical Engineering, South-Central University for Nationalities, Wuhan, China
| | - Xianping Wang
- Hubei Key Laboratory of Edible Wild Plants Conservation and Utilization, College of Life Sciences, Hubei Normal University, Huangshi, China
| | - Chaoyang Cui
- Key Laboratory of Cognitive Science, Laboratory of Membrane Ion Channels and Medicine, College of Biomedical Engineering, South-Central University for Nationalities, Wuhan, China
| | - Yuyang Qin
- Key Laboratory of Cognitive Science, Laboratory of Membrane Ion Channels and Medicine, College of Biomedical Engineering, South-Central University for Nationalities, Wuhan, China
| | - Ziqi Jin
- Key Laboratory of Cognitive Science, Laboratory of Membrane Ion Channels and Medicine, College of Biomedical Engineering, South-Central University for Nationalities, 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
| | - Xiaofei Yang
- Key Laboratory of Cognitive Science, Laboratory of Membrane Ion Channels and Medicine, College of Biomedical Engineering, South-Central University for Nationalities, Wuhan, China
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Jin H, Ge J, Yang J, Zhang Y. Single-Molecule Manipulation Study of Chaperoned SNARE Folding and Assembly with Optical Tweezers. Methods Mol Biol 2022; 2478:461-481. [PMID: 36063331 DOI: 10.1007/978-1-0716-2229-2_17] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Intracellular membrane fusion is primarily driven by coupled folding and assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs). SNARE assembly is intrinsically inefficient and must be chaperoned by a family of evolutionarily and structurally conserved Sec1/Munc-18 (SM) proteins. The physiological pathway of the chaperoned SNARE assembly has not been well understood, partly due to the difficulty in dissecting the many intermediates and pathways of SNARE assembly and measure their associated energetics and kinetics. Optical tweezers have proven to be a powerful tool to characterize the intermediates involved in the chaperoned SNARE assembly. Here, we demonstrate the application of optical tweezers combined with a homemade microfluidic system into studies of synaptic SNARE assembly chaperoned by their cognate SM protein Munc18-1. Three synaptic SNAREs and Munc18-1 constitute the core machinery for synaptic vesicle fusion involved in neurotransmitter release. Many other proteins further regulate the core machinery to enable fusion at the right time and location. The methods described here can be applied to other proteins that regulate SNARE assembly to control membrane fusion involved in numerous biological and physiological processes.
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Affiliation(s)
- Huaizhou Jin
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
- College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, China
| | - Jinghua Ge
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - Jie Yang
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - Yongli Zhang
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA.
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, USA.
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26
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Huber LA. Presenting the FEBS Letters virtual issue on vesicle biology. FEBS Lett 2021; 595:2978-2980. [PMID: 34783009 DOI: 10.1002/1873-3468.14218] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Petrosyan R, Narayan A, Woodside MT. Single-Molecule Force Spectroscopy of Protein Folding. J Mol Biol 2021; 433:167207. [PMID: 34418422 DOI: 10.1016/j.jmb.2021.167207] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Revised: 08/11/2021] [Accepted: 08/11/2021] [Indexed: 10/20/2022]
Abstract
The use of force probes to induce unfolding and refolding of single molecules through the application of mechanical tension, known as single-molecule force spectroscopy (SMFS), has proven to be a powerful tool for studying the dynamics of protein folding. Here we provide an overview of what has been learned about protein folding using SMFS, from small, single-domain proteins to large, multi-domain proteins. We highlight the ability of SMFS to measure the energy landscapes underlying folding, to map complex pathways for native and non-native folding, to probe the mechanisms of chaperones that assist with native folding, to elucidate the effects of the ribosome on co-translational folding, and to monitor the folding of membrane proteins.
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Affiliation(s)
- Rafayel Petrosyan
- Department of Physics, University of Alberta, Edmonton, AB T6G 2E1, Canada
| | - Abhishek Narayan
- Department of Physics, University of Alberta, Edmonton, AB T6G 2E1, Canada
| | - Michael T Woodside
- Department of Physics, University of Alberta, Edmonton, AB T6G 2E1, Canada
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Abstract
SNARE proteins and Sec1/Munc18 (SM) proteins constitute the core molecular engine that drives nearly all intracellular membrane fusion and exocytosis. While SNAREs are known to couple their folding and assembly to membrane fusion, the physiological pathways of SNARE assembly and the mechanistic roles of SM proteins have long been enigmatic. Here, we review recent advances in understanding the SNARE-SM fusion machinery with an emphasis on biochemical and biophysical studies of proteins that mediate synaptic vesicle fusion. We begin by discussing the energetics, pathways, and kinetics of SNARE folding and assembly in vitro. Then, we describe diverse interactions between SM and SNARE proteins and their potential impact on SNARE assembly in vivo. Recent work provides strong support for the idea that SM proteins function as chaperones, their essential role being to enable fast, accurate SNARE assembly. Finally, we review the evidence that SM proteins collaborate with other SNARE chaperones, especially Munc13-1, and briefly discuss some roles of SNARE and SM protein deficiencies in human disease.
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Affiliation(s)
- Yongli Zhang
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06520, USA;
| | - Frederick M Hughson
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA;
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