1
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Zhu M, Xu H, Jin Y, Kong X, Xu B, Liu Y, Yu H. Synaptotagmin-1 undergoes phase separation to regulate its calcium-sensitive oligomerization. J Cell Biol 2024; 223:e202311191. [PMID: 38980206 PMCID: PMC11232894 DOI: 10.1083/jcb.202311191] [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: 12/01/2023] [Revised: 04/17/2024] [Accepted: 06/11/2024] [Indexed: 07/10/2024] Open
Abstract
Synaptotagmin-1 (Syt1) is a calcium sensor that regulates synaptic vesicle fusion in synchronous neurotransmitter release. Syt1 interacts with negatively charged lipids and the SNARE complex to control the fusion event. However, it remains incompletely understood how Syt1 mediates Ca2+-trigged synaptic vesicle fusion. Here, we discovered that Syt1 undergoes liquid-liquid phase separation (LLPS) to form condensates both in vitro and in living cells. Syt1 condensates play a role in vesicle attachment to the PM and efficiently recruit SNAREs and complexin, which may facilitate the downstream synaptic vesicle fusion. We observed that Syt1 condensates undergo a liquid-to-gel-like phase transition, reflecting the formation of Syt1 oligomers. The phase transition can be blocked or reversed by Ca2+, confirming the essential role of Ca2+ in Syt1 oligomer disassembly. Finally, we showed that the Syt1 mutations causing Syt1-associated neurodevelopmental disorder impair the Ca2+-driven phase transition. These findings reveal that Syt1 undergoes LLPS and a Ca2+-sensitive phase transition, providing new insights into Syt1-mediated vesicle fusion.
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Affiliation(s)
- Min Zhu
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| | - Han Xu
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| | - Yulei Jin
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| | - Xiaoxu Kong
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| | - Bingkuan Xu
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| | - Yinghui Liu
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| | - Haijia Yu
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China
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2
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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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3
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Li W, Qin Z, Nand E, Grunst MW, Grover JR, Bess JW, Lifson JD, Zwick MB, Tagare HD, Uchil PD, Mothes W. HIV-1 Env trimers asymmetrically engage CD4 receptors in membranes. Nature 2023; 623:1026-1033. [PMID: 37993716 PMCID: PMC10686830 DOI: 10.1038/s41586-023-06762-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2022] [Accepted: 10/19/2023] [Indexed: 11/24/2023]
Abstract
Human immunodeficiency virus 1 (HIV-1) infection is initiated by binding of the viral envelope glycoprotein (Env) to the cell-surface receptor CD41-4. Although high-resolution structures of Env in a complex with the soluble domains of CD4 have been determined, the binding process is less understood in native membranes5-13. Here we used cryo-electron tomography to monitor Env-CD4 interactions at the membrane-membrane interfaces formed between HIV-1 and CD4-presenting virus-like particles. Env-CD4 complexes organized into clusters and rings, bringing the opposing membranes closer together. Env-CD4 clustering was dependent on capsid maturation. Subtomogram averaging and classification revealed that Env bound to one, two and finally three CD4 molecules, after which Env adopted an open state. Our data indicate that asymmetric HIV-1 Env trimers bound to one and two CD4 molecules are detectable intermediates during virus binding to host cell membranes, which probably has consequences for antibody-mediated immune responses and vaccine immunogen design.
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Affiliation(s)
- Wenwei Li
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, USA.
| | - Zhuan Qin
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, USA
| | - Elizabeth Nand
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, USA
| | - Michael W Grunst
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, USA
| | - Jonathan R Grover
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, USA
| | - Julian W Bess
- AIDS and Cancer Virus Program, Frederick National Laboratory for Cancer Research, Frederick, MD, USA
| | - Jeffrey D Lifson
- AIDS and Cancer Virus Program, Frederick National Laboratory for Cancer Research, Frederick, MD, USA
| | - Michael B Zwick
- Department of Immunology and Microbiology, The Scripps Research Institute, La Jolla, CA, USA
| | - Hemant D Tagare
- Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA
| | - Pradeep D Uchil
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, USA
| | - Walther Mothes
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, USA.
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4
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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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5
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Wehrum S, Siukstaite L, Williamson DJ, Branson TR, Sych T, Madl J, Wildsmith GC, Dai W, Kempmann E, Ross JF, Thomsen M, Webb ME, Römer W, Turnbull WB. Membrane Fusion Mediated by Non-covalent Binding of Re-engineered Cholera Toxin Assemblies to Glycolipids. ACS Synth Biol 2022; 11:3929-3938. [PMID: 36367814 PMCID: PMC9764410 DOI: 10.1021/acssynbio.2c00266] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Membrane fusion is essential for the transport of macromolecules and viruses across membranes. While glycan-binding proteins (lectins) often initiate cellular adhesion, subsequent fusion events require additional protein machinery. No mechanism for membrane fusion arising from simply a protein binding to membrane glycolipids has been described thus far. Herein, we report that a biotinylated protein derived from cholera toxin becomes a fusogenic lectin upon cross-linking with streptavidin. This novel reengineered protein brings about hemifusion and fusion of vesicles as demonstrated by mixing of fluorescently labeled lipids between vesicles as well as content mixing of liposomes filled with fluorescently labeled dextran. Exclusion of the complex at vesicle-vesicle interfaces could also be observed, indicating the formation of hemifusion diaphragms. Discovery of this fusogenic lectin complex demonstrates that new emergent properties can arise from simple changes in protein architecture and provides insights into new mechanisms of lipid-driven fusion.
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Affiliation(s)
- Sarah Wehrum
- Faculty
of Biology, Albert-Ludwigs-University Freiburg, Schänzlestraße 1, 79104 Freiburg, Germany,Bioss-Centre
for Biological Signalling Studies, Albert-Ludwigs-University
Freiburg, Schänzlestraße
18, 79104 Freiburg, Germany
| | - Lina Siukstaite
- Faculty
of Biology, Albert-Ludwigs-University Freiburg, Schänzlestraße 1, 79104 Freiburg, Germany,Bioss-Centre
for Biological Signalling Studies, Albert-Ludwigs-University
Freiburg, Schänzlestraße
18, 79104 Freiburg, Germany
| | - Daniel J. Williamson
- School
of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, LS2 9JT Leeds, U.K..
| | - Thomas R. Branson
- School
of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, LS2 9JT Leeds, U.K..
| | - Taras Sych
- Faculty
of Biology, Albert-Ludwigs-University Freiburg, Schänzlestraße 1, 79104 Freiburg, Germany,Bioss-Centre
for Biological Signalling Studies, Albert-Ludwigs-University
Freiburg, Schänzlestraße
18, 79104 Freiburg, Germany,Freiburg
Center for Interactive Materials and Bioinspired Technology (FIT), Albert-Ludwigs-University Freiburg, Georges-Köhler-Allee 105, 79110 Freiburg, Germany,Science
for Life Laboratory, Department of Women’s and Children’s
Health, Karolinska Institutet, 17165 Solna, Sweden
| | - Josef Madl
- Faculty
of Biology, Albert-Ludwigs-University Freiburg, Schänzlestraße 1, 79104 Freiburg, Germany,Bioss-Centre
for Biological Signalling Studies, Albert-Ludwigs-University
Freiburg, Schänzlestraße
18, 79104 Freiburg, Germany,Freiburg
Center for Interactive Materials and Bioinspired Technology (FIT), Albert-Ludwigs-University Freiburg, Georges-Köhler-Allee 105, 79110 Freiburg, Germany
| | - Gemma C. Wildsmith
- School
of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, LS2 9JT Leeds, U.K..
| | - Wenyue Dai
- School
of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, LS2 9JT Leeds, U.K..
| | - Erik Kempmann
- Faculty
of Biology, Albert-Ludwigs-University Freiburg, Schänzlestraße 1, 79104 Freiburg, Germany,Bioss-Centre
for Biological Signalling Studies, Albert-Ludwigs-University
Freiburg, Schänzlestraße
18, 79104 Freiburg, Germany
| | - James F. Ross
- School
of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, LS2 9JT Leeds, U.K..
| | - Maren Thomsen
- School of
Biomedical Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, LS2 9JT Leeds, U.K..
| | - Michael E. Webb
- School
of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, LS2 9JT Leeds, U.K..
| | - Winfried Römer
- Faculty
of Biology, Albert-Ludwigs-University Freiburg, Schänzlestraße 1, 79104 Freiburg, Germany,Bioss-Centre
for Biological Signalling Studies, Albert-Ludwigs-University
Freiburg, Schänzlestraße
18, 79104 Freiburg, Germany,Freiburg
Center for Interactive Materials and Bioinspired Technology (FIT), Albert-Ludwigs-University Freiburg, Georges-Köhler-Allee 105, 79110 Freiburg, Germany,
| | - W. Bruce Turnbull
- School
of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, LS2 9JT Leeds, U.K..,
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6
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Webster ER, Liu KN, Rawle RJ, Boxer SG. Modulating the Influenza A Virus-Target Membrane Fusion Interface With Synthetic DNA-Lipid Receptors. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:2354-2362. [PMID: 35143209 PMCID: PMC9038422 DOI: 10.1021/acs.langmuir.1c03247] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Influenza A virus (IAV) binds to sialylated glycans on the cell membrane before endocytosis and fusion. Cell-surface glycans are highly heterogeneous in length and glycosylation density, which leads to variations in the distance and rigidity with which IAV is held away from the cell membrane. To gain mechanistic insight into how receptor length and rigidity impact the mechanism of IAV entry, we employed synthetic DNA-lipids as highly tunable surrogate receptors. We tethered IAV to target membranes with a panel of DNA-lipids to investigate the effects of the distance and tether flexibility between virions and target membranes on the kinetics of IAV binding and fusion. Tether length and the presence of a flexible linker led to higher rates of IAV binding, while the efficiencies of lipid and content mixing were typically lower for longer and more rigid DNA tethers. For all DNA tether modifications, we found that the rates of IAV lipid and content mixing were unchanged. These results suggest that variations in the interface between IAV and a target membrane do not significantly impact the rate-limiting step of fusion or the low-pH-triggered engagement of viral fusion peptides with the target membrane. However, our results imply that the flexibility of the viral receptor is important for ensuring that hemifusion events are able to successfully proceed to pore formation.
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Affiliation(s)
- Elizabeth R Webster
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Katherine N Liu
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Robert J Rawle
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Steven G Boxer
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
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7
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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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8
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Radhakrishnan A, Li X, Grushin K, Krishnakumar SS, Liu J, Rothman JE. Symmetrical arrangement of proteins under release-ready vesicles in presynaptic terminals. Proc Natl Acad Sci U S A 2021; 118:e2024029118. [PMID: 33468631 PMCID: PMC7865176 DOI: 10.1073/pnas.2024029118] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Controlled release of neurotransmitters stored in synaptic vesicles (SVs) is a fundamental process that is central to all information processing in the brain. This relies on tight coupling of the SV fusion to action potential-evoked presynaptic Ca2+ influx. This Ca2+-evoked release occurs from a readily releasable pool (RRP) of SVs docked to the plasma membrane (PM). The protein components involved in initial SV docking/tethering and the subsequent priming reactions which make the SV release ready are known. Yet, the supramolecular architecture and sequence of molecular events underlying SV release are unclear. Here, we use cryoelectron tomography analysis in cultured hippocampal neurons to delineate the arrangement of the exocytosis machinery under docked SVs. Under native conditions, we find that vesicles are initially "tethered" to the PM by a variable number of protein densities (∼10 to 20 nm long) with no discernible organization. In contrast, we observe exactly six protein masses, each likely consisting of a single SNAREpin with its bound Synaptotagmins and Complexin, arranged symmetrically connecting the "primed" vesicles to the PM. Our data indicate that the fusion machinery is likely organized into a highly cooperative framework during the priming process which enables rapid SV fusion and neurotransmitter release following Ca2+ influx.
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Affiliation(s)
| | - Xia Li
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT 06520
- Microbial Sciences Institute, Yale University School of Medicine, New Haven, CT 06520
| | - Kirill Grushin
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520
| | - Shyam S Krishnakumar
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520;
| | - Jun Liu
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT 06520;
- Microbial Sciences Institute, Yale University School of Medicine, New Haven, CT 06520
| | - James E Rothman
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520;
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