title: Specific SNARE complex binding mode of the Sec1/Munc-18 protein, Sec1p.
abstract: The Sec1/Munc-18 (SM) family of proteins is required for vesicle fusion in eukaryotic cells and has been linked to the membrane-fusion proteins known as soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs). SM proteins may activate the target-membrane SNARE, syntaxin, for assembly into the fusogenic SNARE complex. In support of an activation role, SM proteins bind directly to their cognate syntaxins. An exception is the yeast Sec1p, which does not bind the yeast plasma-membrane syntaxin, Sso1p. This exception could be explained if the SM interaction motif were blocked by the highly stable closed conformation of Sso1p. We tested the possibility of a latent binding motif using sso1 mutants in yeast and reconstituted the Sec1p binding specificity observed in vivo with purified proteins in vitro. Our results indicate there is no latent binding motif in Sso1p. Instead, Sec1p binds specifically to the ternary SNARE complex, with no detectable binding to the binary t-SNARE complex or any of the three individual SNAREs in their uncomplexed forms. We propose that vesicle fusion requires a specific interaction between the SM protein and the ternary SNARE complex.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA.
authors.forename: John
authors.initials: J
authors.lastname: Togneri
authors.forename: Yi-Shan
authors.initials: YS
authors.lastname: Cheng
authors.forename: Mary
authors.initials: M
authors.lastname: Munson
authors.forename: Frederick M
authors.initials: FM
authors.lastname: Hughson
authors.forename: Chavela M
authors.initials: CM
authors.lastname: Carr
mesh_terms: D046912:Multiprotein Complexes; D051938:Munc18 Proteins / Q000235:genetics / Q000378:metabolism*; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D050765:Qa-SNARE Proteins / Q000235:genetics / Q000378:metabolism; D050600:SNARE Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D046912:Multiprotein Complexes; D051938:Munc18 Proteins; D010455:Peptides; D050765:Qa-SNARE Proteins; C497931:SEC1 protein, S cerevisiae; D050600:SNARE Proteins; C084006:SSO1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins