title: Mechanism and function of synaptotagmin-mediated membrane apposition.
abstract: Synaptotagmin-1 is a Ca(2+) sensor that triggers synchronous neurotransmitter release. The first documented biochemical property of synaptotagmin-1 was its ability to aggregate membranes in response to Ca(2+). However, the mechanism and function of this process were poorly understood. Here we show that synaptotagmin-1-mediated vesicle aggregation is driven by trans interactions between synaptotagmin-1 molecules bound to different membranes. We found a strong correlation between the ability of Ca(2+)-bound synaptotagmin-1 to aggregate vesicles and to stimulate SNARE-mediated membrane fusion. Moreover, artificial aggregation of membranes-using non-synaptotagmin proteins-also efficiently promoted fusion of SNARE-bearing liposomes. Finally, using a modified fusion assay, we observed that synaptotagmin-1 drove the assembly of otherwise non-fusogenic individual t-SNARE proteins into fusion-competent heterodimers, independently of aggregation. Thus, membrane aggregation and t-SNARE assembly appear to be two key aspects of fusion reactions that are regulated by Ca(2+)-bound synaptotagmin-1 and catalyzed by SNAREs.
authors.affiliation: Howard Hughes Medical Institute and Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, USA.
authors.forename: Enfu
authors.initials: E
authors.lastname: Hui
authors.forename: Jon D
authors.initials: JD
authors.lastname: Gaffaney
authors.forename: Zhao
authors.initials: Z
authors.lastname: Wang
authors.forename: Colin P
authors.initials: CP
authors.lastname: Johnson
authors.forename: Chantell S
authors.initials: CS
authors.lastname: Evans
authors.forename: Edwin R
authors.initials: ER
authors.lastname: Chapman
mesh_terms: D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D019281:Dimerization; D031541:Fluorescence Resonance Energy Transfer; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008561:Membrane Fusion / Q000502:physiology; D051379:Mice; D008954:Models, Biological; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D050765:Qa-SNARE Proteins / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D050600:SNARE Proteins / Q000378:metabolism / Q000502:physiology; D050825:Synaptosomal-Associated Protein 25 / Q000737:chemistry / Q000378:metabolism; D050863:Synaptotagmin I / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*
chemical_list: D008081:Liposomes; D050765:Qa-SNARE Proteins; D050600:SNARE Proteins; C494210:Snap25 protein, rat; D050825:Synaptosomal-Associated Protein 25; D050863:Synaptotagmin I; C494312:Syt1 protein, rat; D002118:Calcium