title: Molecular dissection of the Munc18c/syntaxin4 interaction: implications for regulation of membrane trafficking.
abstract: Sec1p/Munc18 (SM) proteins are believed to play an integral role in vesicle transport through their interaction with SNAREs. Different SM proteins have been shown to interact with SNAREs via different mechanisms, leading to the conclusion that their function has diverged. To further explore this notion, in this study, we have examined the molecular interactions between Munc18c and its cognate SNAREs as these molecules are ubiquitously expressed in mammals and likely regulate a universal plasma membrane trafficking step. Thus, Munc18c binds to monomeric syntaxin4 and the N-terminal 29 amino acids of syntaxin4 are necessary for this interaction. We identified key residues in Munc18c and syntaxin4 that determine the N-terminal interaction and that are consistent with the N-terminal binding mode of yeast proteins Sly1p and Sed5p. In addition, Munc18c binds to the syntaxin4/SNAP23/VAMP2 SNARE complex. Pre-assembly of the syntaxin4/Munc18c dimer accelerates the formation of SNARE complex compared to assembly with syntaxin4 alone. These data suggest that Munc18c interacts with its cognate SNAREs in a manner that resembles the yeast proteins Sly1p and Sed5p rather than the mammalian neuronal proteins Munc18a and syntaxin1a. The Munc18c-SNARE interactions described here imply that Munc18c could play a positive regulatory role in SNARE assembly.
authors.affiliation: Institute for Molecular Bioscience and ARC Special Research Centre for Functional and Applied Genomics, University of Queensland, Brisbane, Queensland 4072, Australia.
authors.forename: Catherine F
authors.initials: CF
authors.lastname: Latham
authors.forename: Jamie A
authors.initials: JA
authors.lastname: Lopez
authors.forename: Shu-Hong
authors.initials: SH
authors.lastname: Hu
authors.forename: Christine L
authors.initials: CL
authors.lastname: Gee
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Westbury
authors.forename: Duncan H
authors.initials: DH
authors.lastname: Blair
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Armishaw
authors.forename: Paul F
authors.initials: PF
authors.lastname: Alewood
authors.forename: Nia J
authors.initials: NJ
authors.lastname: Bryant
authors.forename: David E
authors.initials: DE
authors.lastname: James
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Martin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D051938:Munc18 Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D050765:Qa-SNARE Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D050766:Qb-SNARE Proteins / Q000378:metabolism; D050767:Qc-SNARE Proteins / Q000378:metabolism; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D050600:SNARE Proteins / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D050988:Vesicle-Associated Membrane Protein 2 / Q000378:metabolism
chemical_list: D051938:Munc18 Proteins; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D011993:Recombinant Fusion Proteins; C072520:SLY1 protein, S cerevisiae; C100493:SNAP23 protein, human; D050600:SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; C497943:Stxbp3 protein, mouse; D050988:Vesicle-Associated Membrane Protein 2