Mso1p regulates membrane fusion through interactions with the putative N-peptide-binding area in Sec1p domain 1.
Sec1p/Munc18 (SM) family proteins regulate SNARE complex function in membrane fusion through their interactions with syntaxins. In addition to syntaxins, only a few SM protein interacting proteins are known and typically, their binding modes with SM proteins are poorly characterized. We previously identified Mso1p as a Sec1p-binding protein and showed that it is involved in membrane fusion regulation. Here we demonstrate that Mso1p and Sec1p interact at sites of exocytosis and that the Mso1p-Sec1p interaction site depends on a functional Rab GTPase Sec4p and its GEF Sec2p. Random and targeted mutagenesis of Sec1p, followed by analysis of protein interactions, indicates that Mso1p interacts with Sec1p domain 1 and that this interaction is important for membrane fusion. In many SM family proteins, domain 1 binds to a N-terminal peptide of a syntaxin family protein. The Sec1p-interacting syntaxins Sso1p and Sso2p lack the N-terminal peptide. We show that the putative N-peptide binding area in Sec1p domain 1 is important for Mso1p binding, and that Mso1p can interact with Sso1p and Sso2p. Our results suggest that Mso1p mimics N-peptide binding to facilitate membrane fusion.
Weber
Marion
M
Research Program in Cell and Molecular Biology, Institute of Biotechnology, University of Helsinki, 00014 Helsinki, Finland.
Chernov
Konstantin
K
Turakainen
Hilkka
H
Wohlfahrt
Gerd
G
Pajunen
Maria
M
Savilahti
Harri
H
Jäntti
Jussi
J
D019943:Amino Acid Substitution / Q000235:genetics; D001665:Binding Sites; D008561:Membrane Fusion; D008565:Membrane Proteins / Q000378:metabolism*; D008958:Models, Molecular; D051938:Munc18 Proteins / Q000737:chemistry* / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D010455:Peptides / Q000378:metabolism*; D011485:Protein Binding; D025941:Protein Interaction Mapping; D055550:Protein Stability; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D050765:Qa-SNARE Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism*; D013172:Spores, Fungal / Q000166:cytology / Q000378:metabolism
C106953:MSO1 protein, S cerevisiae; D008565:Membrane Proteins; D051938:Munc18 Proteins; D010455:Peptides; D050765:Qa-SNARE Proteins; C497931:SEC1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins