Molecular interactions position Mso1p, a novel PTB domain homologue, in the interface of the exocyst complex and the exocytic SNARE machinery in yeast.
In this study, we have analyzed the association of the Sec1p interacting protein Mso1p with the membrane fusion machinery in yeast. We show that Mso1p is essential for vesicle fusion during prospore membrane formation. Green fluorescent protein-tagged Mso1p localizes to the sites of exocytosis and at the site of prospore membrane formation. In vivo and in vitro experiments identified a short amino-terminal sequence in Mso1p that mediates its interaction with Sec1p and is needed for vesicle fusion. A point mutation, T47A, within the Sec1p-binding domain abolishes Mso1p functionality in vivo, and mso1T47A mutant cells display specific genetic interactions with sec1 mutants. Mso1p coimmunoprecipitates with Sec1p, Sso1/2p, Snc1/2p, Sec9p, and the exocyst complex subunit Sec15p. In sec4-8 and SEC4I133 mutant cells, association of Mso1p with Sso1/2p, Snc1/2p, and Sec9p is affected, whereas interaction with Sec1p persists. Furthermore, in SEC4I133 cells the dominant negative Sec4I133p coimmunoprecipitates with Mso1p-Sec1p complex. Finally, we identify Mso1p as a homologue of the PTB binding domain of the mammalian Sec1p binding Mint proteins. These results position Mso1p in the interface of the exocyst complex, Sec4p, and the SNARE machinery, and reveal a novel layer of molecular conservation in the exocytosis machinery.
Knop
Michael
M
EMBL, Heidelberg D-69117, Germany. knop@embl.de
Miller
K Juha
KJ
Mazza
Massimiliano
M
Feng
DeJiang
D
Weber
Marion
M
Keränen
Sirkka
S
Jäntti
Jussi
J
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics; D000595:Amino Acid Sequence; D005089:Exocytosis; D008561:Membrane Fusion / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D051938:Munc18 Proteins / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000235:genetics; D017354:Point Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D050600:SNARE Proteins / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000502:physiology*; D022142:Secretory Vesicles / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D020798:Two-Hybrid System Techniques; D020691:rab GTP-Binding Proteins / Q000502:physiology
D048868:Adaptor Proteins, Signal Transducing; C106953:MSO1 protein, S cerevisiae; D008565:Membrane Proteins; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins; C497931:SEC1 protein, S cerevisiae; D050600:SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; C064320:SEC4 protein, S cerevisiae; D020691:rab GTP-Binding Proteins