title: SNARE complex formation is triggered by Ca2+ and drives membrane fusion.
abstract: Neurotransmitter exocytosis, a process mediated by a core complex of syntaxin, SNAP-25, and VAMP (SNAREs), is inhibited by SNARE-cleaving neurotoxins. Botulinum neurotoxin E inhibition of norepinephrine release in permeabilized PC12 cells can be rescued by adding a 65 aa C-terminal fragment of SNAP-25 (S25-C). Mutations along the hydrophobic face of the S25-C helix result in SNARE complexes with different thermostabilities, and these mutants rescue exocytosis to different extents. Rescue depends on the continued presence of both S25-C and Ca2+ and correlates with complex formation. The data suggest that Ca2+ triggers S25-C binding to a low-affinity site, initiating trans-complex formation. Pairing of SNARE proteins on apposing membranes leads to bilayer fusion and results in a high-affinity cis-SNARE complex.
authors.affiliation: Howard Hughes Medical Institute, Department of Molecular and Cellular Physiology, Stanford University School of Medicine, California 94305-5345, USA.
authors.forename: Y A
authors.initials: YA
authors.lastname: Chen
authors.forename: S J
authors.initials: SJ
authors.lastname: Scales
authors.forename: S M
authors.initials: SM
authors.lastname: Patel
authors.forename: Y C
authors.initials: YC
authors.lastname: Doung
authors.forename: R H
authors.initials: RH
authors.lastname: Scheller
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001905:Botulinum Toxins / Q000633:toxicity; D002118:Calcium / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology; D046911:Macromolecular Substances; D008561:Membrane Fusion / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016716:PC12 Cells; D051381:Rats; D050600:SNARE Proteins; D050825:Synaptosomal-Associated Protein 25; D033921:Vesicular Transport Proteins
chemical_list: D017931:DNA Primers; D046911:Macromolecular Substances; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050600:SNARE Proteins; C494209:Snap25 protein, mouse; C494210:Snap25 protein, rat; D050825:Synaptosomal-Associated Protein 25; D033921:Vesicular Transport Proteins; D001905:Botulinum Toxins; D002118:Calcium; C096326:botulinum toxin type E