title: Sec3 promotes the initial binary t-SNARE complex assembly and membrane fusion.
abstract: The soluble N-ethylmaleimide-sensitive factor-attachment protein receptors (SNAREs) constitute the core machinery for membrane fusion during eukaryotic cell vesicular trafficking. However, how the assembly of the SNARE complex is initiated is unknown. Here we report that Sec3, a component of the exocyst complex that mediates vesicle tethering during exocytosis, directly interacts with the t-SNARE protein Sso2. This interaction promotes the formation of an Sso2-Sec9 'binary' t-SNARE complex, the early rate-limiting step in SNARE complex assembly, and stimulates membrane fusion. The crystal structure of the Sec3-Sso2 complex suggests that Sec3 binding induces conformational changes of Sso2 that are crucial for the relief of its auto-inhibition. Interestingly, specific disruption of the Sec3-Sso2 interaction in cells blocks exocytosis without affecting the function of Sec3 in vesicle tethering. Our study reveals an activation mechanism for SNARE complex assembly, and uncovers a role of the exocyst in promoting membrane fusion in addition to vesicle tethering.
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Peng
authors.initials: P
authors.lastname: Yue
authors.affiliation: Department of Medical Biochemistry, Max F. Perutz Laboratories, Medical University of Vienna, 1030 Vienna, Austria.
authors.forename: Yubo
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Kunrong
authors.initials: K
authors.lastname: Mei
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Shaoxiao
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Medical Biochemistry, Max F. Perutz Laboratories, Medical University of Vienna, 1030 Vienna, Austria.
authors.forename: Johannes
authors.initials: J
authors.lastname: Lesigang
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Yueyao
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Department of Medical Biochemistry, Max F. Perutz Laboratories, Medical University of Vienna, 1030 Vienna, Austria.
authors.forename: Gang
authors.initials: G
authors.lastname: Dong
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Guo
mesh_terms: D002457:Cell Extracts; D002462:Cell Membrane; D003460:Crystallization; D005786:Gene Expression Regulation; D015966:Gene Expression Regulation, Fungal / Q000502:physiology; D008081:Liposomes; D008561:Membrane Fusion / Q000502:physiology*; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D050765:Qa-SNARE Proteins / Q000235:genetics / Q000378:metabolism*; D050600:SNARE Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D002457:Cell Extracts; D008081:Liposomes; D050765:Qa-SNARE Proteins; C103130:SEC3 protein, S cerevisiae; D050600:SNARE Proteins; C084006:SSO1 protein, S cerevisiae; C084007:SSO2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins