1
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Duan M, Plemel RL, Takenaka T, Lin A, Delgado BM, Nattermann U, Nickerson DP, Mima J, Miller EA, Merz AJ. SNARE chaperone Sly1 directly mediates close-range vesicle tethering. J Cell Biol 2024; 223:e202001032. [PMID: 38478018 PMCID: PMC10943277 DOI: 10.1083/jcb.202001032] [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: 01/16/2020] [Revised: 12/20/2023] [Accepted: 02/22/2024] [Indexed: 03/17/2024] Open
Abstract
The essential Golgi protein Sly1 is a member of the Sec1/mammalian Unc-18 (SM) family of SNARE chaperones. Sly1 was originally identified through remarkable gain-of-function alleles that bypass requirements for diverse vesicle tethering factors. Employing genetic analyses and chemically defined reconstitutions of ER-Golgi fusion, we discovered that a loop conserved among Sly1 family members is not only autoinhibitory but also acts as a positive effector. An amphipathic lipid packing sensor (ALPS)-like helix within the loop directly binds high-curvature membranes. Membrane binding is required for relief of Sly1 autoinhibition and also allows Sly1 to directly tether incoming vesicles to the Qa-SNARE on the target organelle. The SLY1-20 mutation bypasses requirements for diverse tethering factors but loses this ability if the tethering activity is impaired. We propose that long-range tethers, including Golgins and multisubunit tethering complexes, hand off vesicles to Sly1, which then tethers at close range to initiate trans-SNARE complex assembly and fusion in the early secretory pathway.
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Affiliation(s)
- Mengtong Duan
- Department of Biochemistry, University of Washington, Seattle, WA, USA
| | - Rachael L. Plemel
- Department of Biochemistry, University of Washington, Seattle, WA, USA
| | | | - Ariel Lin
- Department of Biochemistry, University of Washington, Seattle, WA, USA
- Department of Biology, California State University, San Bernardino, CA, USA
| | | | - Una Nattermann
- Department of Biochemistry, University of Washington, Seattle, WA, USA
- Biophysics, Structure, and Design Graduate Program, University of Washington, Seattle, WA, USA
- Institute for Protein Design, University of Washington, Seattle, WA, USA
| | | | - Joji Mima
- Institute for Protein Research, Osaka University, Osaka, Japan
| | | | - Alexey J. Merz
- Department of Biochemistry, University of Washington, Seattle, WA, USA
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2
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Ricardi MM, Wallmeroth N, Cermesoni C, Mehlhorn DG, Richter S, Zhang L, Mittendorf J, Godehardt I, Berendzen KW, von Roepenack-Lahaye E, Stierhof YD, Lipka V, Jürgens G, Grefen C. A tyrosine phospho-switch within the Longin domain of VAMP721 modulates SNARE functionality. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2023; 116:1633-1651. [PMID: 37659090 DOI: 10.1111/tpj.16451] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Revised: 08/08/2023] [Accepted: 08/16/2023] [Indexed: 09/04/2023]
Abstract
The final step in secretion is membrane fusion facilitated by SNARE proteins that reside in opposite membranes. The formation of a trans-SNARE complex between one R and three Q coiled-coiled SNARE domains drives the final approach of the membranes providing the mechanical energy for fusion. Biological control of this mechanism is exerted by additional domains within some SNAREs. For example, the N-terminal Longin domain (LD) of R-SNAREs (also called Vesicle-associated membrane proteins, VAMPs) can fold back onto the SNARE domain blocking interaction with other cognate SNAREs. The LD may also determine the subcellular localization via interaction with other trafficking-related proteins. Here, we provide cell-biological and genetic evidence that phosphorylation of the Tyrosine57 residue regulates the functionality of VAMP721. We found that an aspartate mutation mimics phosphorylation, leading to protein instability and subsequent degradation in lytic vacuoles. The mutant SNARE also fails to rescue the defects of vamp721vamp722 loss-of-function lines in spite of its wildtype-like localization within the secretory pathway and the ability to interact with cognate SNARE partners. Most importantly, it imposes a dominant negative phenotype interfering with root growth, normal secretion and cytokinesis in wildtype plants generating large aggregates that mainly contain secretory vesicles. Non-phosphorylatable VAMP721Y57F needs higher gene dosage to rescue double mutants in comparison to native VAMP721 underpinning that phosphorylation modulates SNARE function. We propose a model where short-lived phosphorylation of Y57 serves as a regulatory step to control VAMP721 activity, favoring its open state and interaction with cognate partners to ultimately drive membrane fusion.
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Affiliation(s)
- Martiniano Maria Ricardi
- Ruhr University Bochum, Faculty of Biology and Biotechnology, Bochum, Germany
- Departamento de Fisiología y Biología Molecular y Celular (FBMC), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina
- Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE), CONICET-Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Niklas Wallmeroth
- University of Tübingen, ZMBP Developmental Genetics, Tübingen, Germany
| | - Cecilia Cermesoni
- Departamento de Fisiología y Biología Molecular y Celular (FBMC), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina
- Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE), CONICET-Universidad de Buenos Aires, Buenos Aires, Argentina
| | | | - Sandra Richter
- University of Tübingen, ZMBP Developmental Genetics, Tübingen, Germany
- University of Tübingen, ZMBP Central Facilities, Tübingen, Germany
| | - Lei Zhang
- Ruhr University Bochum, Faculty of Biology and Biotechnology, Bochum, Germany
| | - Josephine Mittendorf
- University of Göttingen, Albrecht-von-Haller-Institute of Plant Sciences, Göttingen, Germany
| | - Ingeborg Godehardt
- Ruhr University Bochum, Faculty of Biology and Biotechnology, Bochum, Germany
| | | | | | | | - Volker Lipka
- University of Göttingen, Albrecht-von-Haller-Institute of Plant Sciences, Göttingen, Germany
| | - Gerd Jürgens
- University of Tübingen, ZMBP Developmental Genetics, Tübingen, Germany
| | - Christopher Grefen
- Ruhr University Bochum, Faculty of Biology and Biotechnology, Bochum, Germany
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3
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Hodgens C, Flaherty DT, Pullen AM, Khan I, English NJ, Gillan L, Rojas-Pierce M, Akpa BS. Model-based inference of a plant-specific dual role for HOPS in regulating guard cell vacuole fusion. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.11.07.565947. [PMID: 37986942 PMCID: PMC10659295 DOI: 10.1101/2023.11.07.565947] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2023]
Abstract
Stomata are the pores on a leaf surface that regulate gas exchange. Each stoma consists of two guard cells whose movements regulate pore opening and thereby control CO2 fixation and water loss. Guard cell movements depend in part on the remodeling of vacuoles, which have been observed to change from a highly fragmented state to a fused morphology during stomata opening. This change in morphology requires a membrane fusion mechanism that responds rapidly to environmental signals, allowing plants to respond to diurnal and stress cues. With guard cell vacuoles being both large and responsive to external signals, stomata represent a unique system in which to delineate mechanisms of membrane fusion. Fusion of vacuole membranes is a highly conserved process in eukaryotes, with key roles played by two multi-subunit complexes: HOPS (homotypic fusion and vacuolar protein sorting) and SNARE (soluble NSF attachment protein receptor). HOPS is a vacuole tethering factor that is thought to chaperone SNAREs from apposing vacuole membranes into a fusion-competent complex capable of rearranging membranes. To resolve a counter-intuitive observation regarding the role of HOPS in regulating plant vacuole morphology, we derived a quantitative model of vacuole fusion dynamics and used it to generate testable predictions about HOPS-SNARE interactions. We derived our model by applying simulation-based inference to integrate prior knowledge about molecular interactions with limited, qualitative observations of emergent vacuole phenotypes. By constraining the model parameters to yield the emergent outcomes observed for stoma opening - as induced by two distinct chemical treatments - we predicted a dual role for HOPS and identified a stalled form of the SNARE complex that differs from phenomena reported in yeast. We predict that HOPS has contradictory actions at different points in the fusion signaling pathway, promoting the formation of SNARE complexes, but limiting their activity.
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Affiliation(s)
- Charles Hodgens
- Department of Chemical and Biomolecular Engineering, University of Tennessee-Knoxville, Knoxville, Tennessee, USA
| | - DT Flaherty
- Department of Molecular Biomedical Sciences, North Carolina State University, Raleigh, North Carolina, USA
| | - Anne-Marie Pullen
- Department of Plant and Microbial Biology, North Carolina State University, Raleigh, North Carolina, USA
| | - Imran Khan
- Department of Plant and Microbial Biology, North Carolina State University, Raleigh, North Carolina, USA
| | - Nolan J English
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Lydia Gillan
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, USA
| | - Marcela Rojas-Pierce
- Department of Plant and Microbial Biology, North Carolina State University, Raleigh, North Carolina, USA
| | - Belinda S Akpa
- Department of Chemical and Biomolecular Engineering, University of Tennessee-Knoxville, Knoxville, Tennessee, USA
- Department of Molecular Biomedical Sciences, North Carolina State University, Raleigh, North Carolina, USA
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
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4
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Orr A, Wickner W. MARCKS Effector Domain, a reversible lipid ligand, illuminates late stages of membrane fusion. Mol Biol Cell 2023; 34:ar123. [PMID: 37672336 PMCID: PMC10846624 DOI: 10.1091/mbc.e23-06-0228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Revised: 08/28/2023] [Accepted: 08/30/2023] [Indexed: 09/08/2023] Open
Abstract
Yeast vacuolar HOPS tethers membranes, catalyzes trans-SNARE assembly between R- and Q-SNAREs, and shepherds SNAREs past early inhibition by Sec17. After partial SNARE zippering, fusion is driven slowly by either completion of SNARE zippering or by Sec17/Sec18, but rapid fusion needs zippering and Sec17/Sec18. Using reconstituted-vacuolar fusion, we find that MARCKS Effector Domain (MED) peptide, a lipid ligand, blocks fusion reversibly at a late reaction stage. The MED fusion blockade is overcome by either salt extraction, inactivation with the MED ligand calmodulin, or addition of Sec17/Sec18. During incubation with MED, SNAREs assemble stable complexes in trans and fusion becomes resistant to antibody to the Qa SNARE. When Q-SNAREs are preassembled, a synthetic tether can replace HOPS for fusion. With a synthetic tether, fusion needs both complete SNARE zippering and Sec17/Sec18 to overcome a MED block. In contrast, when SNARE domains are only two-third zippered, only HOPS will support Sec17/Sec18 driven fusion without needing complete zippering. HOPS thus remains engaged with SNAREs during zippering. MED facilitates the study of distinct fusion stages: tethering, initial trans-SNARE assembly and its sensitivity to Sec17, SNARE zippering, Sec17/Sec18 engagement, and lipid and lumenal mixing.
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Affiliation(s)
- Amy Orr
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755-3844
| | - William Wickner
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755-3844
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5
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Buzzatto MV, Berberián MV, Di Bartolo AL, Masone D, Tomes CN. α-Synuclein is required for sperm exocytosis at a post-fusion stage. Front Cell Dev Biol 2023; 11:1125988. [PMID: 37287458 PMCID: PMC10242118 DOI: 10.3389/fcell.2023.1125988] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Accepted: 05/09/2023] [Indexed: 06/09/2023] Open
Abstract
The sperm acrosome is a large dense-core granule whose contents are secreted by regulated exocytosis at fertilization through the opening of numerous fusion pores between the acrosomal and plasma membranes. In other cells, the nascent pore generated when the membrane surrounding a secretory vesicle fuses with the plasma membrane may have different fates. In sperm, pore dilation leads to the vesiculation and release of these membranes, together with the granule contents. α-Synuclein is a small cytosolic protein claimed to exhibit different roles in exocytic pathways in neurons and neuroendocrine cells. Here, we scrutinized its function in human sperm. Western blot revealed the presence of α-synuclein and indirect immunofluorescence its localization to the acrosomal domain of human sperm. Despite its small size, the protein was retained following permeabilization of the plasma membrane with streptolysin O. α-Synuclein was required for acrosomal release, as demonstrated by the inability of an inducer to elicit exocytosis when permeabilized human sperm were loaded with inhibitory antibodies to human α-synuclein. The antibodies halted calcium-induced secretion when introduced after the acrosome docked to the cell membrane. Two functional assays, fluorescence and transmission electron microscopies revealed that the stabilization of open fusion pores was responsible for the secretion blockage. Interestingly, synaptobrevin was insensitive to neurotoxin cleavage at this point, an indication of its engagement in cis SNARE complexes. The very existence of such complexes during AE reflects a new paradigm. Recombinant α-synuclein rescued the inhibitory effects of the anti-α-synuclein antibodies and of a chimeric Rab3A-22A protein that also inhibits AE after fusion pore opening. We applied restrained molecular dynamics simulations to compare the energy cost of expanding a nascent fusion pore between two model membranes and found it higher in the absence than in the presence of α-synuclein. Hence, our results suggest that α-synuclein is essential for expanding fusion pores.
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Affiliation(s)
- Micaela Vanina Buzzatto
- Instituto de Histología y Embriología de Mendoza (IHEM)-CONICET-Universidad Nacional de Cuyo, Mendoza, Argentina
- Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Cuyo, Mendoza, Argentina
| | - María Victoria Berberián
- Instituto de Histología y Embriología de Mendoza (IHEM)-CONICET-Universidad Nacional de Cuyo, Mendoza, Argentina
- Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Cuyo, Mendoza, Argentina
- Instituto de Ciencias Básicas (ICB)-CONICET-Universidad Nacional de Cuyo, Mendoza, Argentina
| | - Ary Lautaro Di Bartolo
- Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Cuyo, Mendoza, Argentina
| | - Diego Masone
- Instituto de Histología y Embriología de Mendoza (IHEM)-CONICET-Universidad Nacional de Cuyo, Mendoza, Argentina
- Facultad de Ingeniería, Universidad Nacional de Cuyo, Mendoza, Argentina
| | - Claudia Nora Tomes
- Instituto de Histología y Embriología de Mendoza (IHEM)-CONICET-Universidad Nacional de Cuyo, Mendoza, Argentina
- Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Cuyo, Mendoza, Argentina
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6
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Yan C, Jiang J, Yang Y, Geng X, Dong W. The function of VAMP2 in mediating membrane fusion: An overview. Front Mol Neurosci 2022; 15:948160. [PMID: 36618823 PMCID: PMC9816800 DOI: 10.3389/fnmol.2022.948160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Accepted: 12/05/2022] [Indexed: 12/24/2022] Open
Abstract
Vesicle-associated membrane protein 2 (VAMP2, also known as synaptobrevin-2), encoded by VAMP2 in humans, is a key component of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex. VAMP2 combined with syntaxin-1A (SYX-1A) and synaptosome-associated protein 25 (SNAP-25) produces a force that induces the formation of fusion pores, thereby mediating the fusion of synaptic vesicles and the release of neurotransmitters. VAMP2 is largely unstructured in the absence of interaction partners. Upon interaction with other SNAREs, the structure of VAMP2 stabilizes, resulting in the formation of four structural domains. In this review, we highlight the current knowledge of the roles of the VAMP2 domains and the interaction between VAMP2 and various fusion-related proteins in the presynaptic cytoplasm during the fusion process. Our summary will contribute to a better understanding of the roles of the VAMP2 protein in membrane fusion.
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Affiliation(s)
- Chong Yan
- Key Laboratory of Medical Electrophysiology, Ministry of Education and Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou, Sichuan, China
| | - Jie Jiang
- Key Laboratory of Medical Electrophysiology, Ministry of Education and Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou, Sichuan, China
| | - Yuan Yang
- Key Laboratory of Medical Electrophysiology, Ministry of Education and Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou, Sichuan, China
| | - Xiaoqi Geng
- Department of Neurosurgery, Neurosurgical Clinical Research Center of Sichuan Province, Affiliated Hospital of Southwest Medical University, Luzhou, China,*Correspondence: Xiaoqi Geng,
| | - Wei Dong
- Key Laboratory of Medical Electrophysiology, Ministry of Education and Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou, Sichuan, China,Wei Dong,
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7
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Gingras RM, Sulpizio AM, Park J, Bretscher A. High-resolution secretory timeline from vesicle formation at the Golgi to fusion at the plasma membrane in S. cerevisiae. eLife 2022; 11:e78750. [PMID: 36331188 PMCID: PMC9671497 DOI: 10.7554/elife.78750] [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: 03/18/2022] [Accepted: 11/03/2022] [Indexed: 11/06/2022] Open
Abstract
Most of the components in the yeast secretory pathway have been studied, yet a high-resolution temporal timeline of their participation is lacking. Here, we define the order of acquisition, lifetime, and release of critical components involved in late secretion from the Golgi to the plasma membrane. Of particular interest is the timing of the many reported effectors of the secretory vesicle Rab protein Sec4, including the myosin-V Myo2, the exocyst complex, the lgl homolog Sro7, and the small yeast-specific protein Mso1. At the trans-Golgi network (TGN) Sec4's GEF, Sec2, is recruited to Ypt31-positive compartments, quickly followed by Sec4 and Myo2 and vesicle formation. While transported to the bud tip, the entire exocyst complex, including Sec3, is assembled on to the vesicle. Before fusion, vesicles tether for 5 s, during which the vesicle retains the exocyst complex and stimulates lateral recruitment of Rho3 on the plasma membrane. Sec2 and Myo2 are rapidly lost, followed by recruitment of cytosolic Sro7, and finally the SM protein Sec1, which appears for just 2 s prior to fusion. Perturbation experiments reveal an ordered and robust series of events during tethering that provide insights into the function of Sec4 and effector exchange.
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Affiliation(s)
- Robert M Gingras
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell UniversityIthacaUnited States
| | - Abigail M Sulpizio
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell UniversityIthacaUnited States
| | - Joelle Park
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell UniversityIthacaUnited States
| | - Anthony Bretscher
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell UniversityIthacaUnited States
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8
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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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9
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Luo C, Shi Y, Xiang Y. SNAREs Regulate Vesicle Trafficking During Root Growth and Development. FRONTIERS IN PLANT SCIENCE 2022; 13:853251. [PMID: 35360325 PMCID: PMC8964185 DOI: 10.3389/fpls.2022.853251] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2022] [Accepted: 01/27/2022] [Indexed: 05/13/2023]
Abstract
SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins assemble to drive the final membrane fusion step of membrane trafficking. Thus, SNAREs are essential for membrane fusion and vesicular trafficking, which are fundamental mechanisms for maintaining cellular homeostasis. In plants, SNAREs have been demonstrated to be located in different subcellular compartments and involved in a variety of fundamental processes, such as cytokinesis, cytoskeleton organization, symbiosis, and biotic and abiotic stress responses. In addition, SNAREs can also contribute to the normal growth and development of Arabidopsis. Here, we review recent progress in understanding the biological functions and signaling network of SNAREs in vesicle trafficking and the regulation of root growth and development in Arabidopsis.
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10
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Song H, Torng TL, Orr AS, Brunger AT, Wickner WT. Sec17/Sec18 can support membrane fusion without help from completion of SNARE zippering. eLife 2021; 10:67578. [PMID: 33944780 PMCID: PMC8143792 DOI: 10.7554/elife.67578] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Accepted: 04/30/2021] [Indexed: 11/20/2022] Open
Abstract
Membrane fusion requires R-, Qa-, Qb-, and Qc-family SNAREs that zipper into RQaQbQc coiled coils, driven by the sequestration of apolar amino acids. Zippering has been thought to provide all the force driving fusion. Sec17/αSNAP can form an oligomeric assembly with SNAREs with the Sec17 C-terminus bound to Sec18/NSF, the central region bound to SNAREs, and a crucial apolar loop near the N-terminus poised to insert into membranes. We now report that Sec17 and Sec18 can drive robust fusion without requiring zippering completion. Zippering-driven fusion is blocked by deleting the C-terminal quarter of any Q-SNARE domain or by replacing the apolar amino acids of the Qa-SNARE that face the center of the 4-SNARE coiled coils with polar residues. These blocks, singly or combined, are bypassed by Sec17 and Sec18, and SNARE-dependent fusion is restored without help from completing zippering.
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Affiliation(s)
- Hongki Song
- Department of Biochemistry and Cell Biology Geisel School of Medicine at Dartmouth, Hanover, United States
| | - Thomas L Torng
- Department of Biochemistry and Cell Biology Geisel School of Medicine at Dartmouth, Hanover, United States
| | - Amy S Orr
- Department of Biochemistry and Cell Biology Geisel School of Medicine at Dartmouth, Hanover, United States
| | - Axel T Brunger
- Howard Hughes Medical Institute and Department of Molecular and Cellular Physiology Stanford University, Stanford, United States
| | - William T Wickner
- Department of Biochemistry and Cell Biology Geisel School of Medicine at Dartmouth, Hanover, United States
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