title: Vacuole membrane fusion: V0 functions after trans-SNARE pairing and is coupled to the Ca2+-releasing channel.
abstract: Pore models of membrane fusion postulate that cylinders of integral membrane proteins can initiate a fusion pore after conformational rearrangement of pore subunits. In the fusion of yeast vacuoles, V-ATPase V0 sectors, which contain a central cylinder of membrane integral proteolipid subunits, associate to form a transcomplex that might resemble an intermediate postulated in some pore models. We tested the role of V0 sectors in vacuole fusion. V0 functions in fusion and proton translocation could be experimentally separated via the differential effects of mutations and inhibitory antibodies. Inactivation of the V0 subunit Vph1p blocked fusion in the terminal reaction stage that is independent of a proton gradient. Deltavph1 mutants were capable of docking and trans-SNARE pairing and of subsequent release of lumenal Ca2+, but they did not fuse. The Ca2+-releasing channel appears to be tightly coupled to V0 because inactivation of Vph1p by antibodies blocked Ca2+ release. Vph1 deletion on only one fusion partner sufficed to severely reduce fusion activity. The functional requirement for Vph1p correlates to V0 transcomplex formation in that both occur after docking and Ca2+ release. These observations establish V0 as a crucial factor in vacuole fusion acting downstream of trans-SNARE pairing.
authors.affiliation: Friedrich-Miescher-Laboratorium der Max-Planck-Gesellschaft, 72076 Tübingen, Germany.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Bayer
authors.forename: Christoph
authors.initials: C
authors.lastname: Reese
authors.forename: Susanne
authors.initials: S
authors.lastname: Buhler
authors.forename: Christopher
authors.initials: C
authors.lastname: Peters
authors.forename: Andreas
authors.initials: A
authors.lastname: Mayer
mesh_terms: D000165:Acridine Orange; D002118:Calcium / Q000378:metabolism*; D005456:Fluorescent Dyes; D007700:Kinetics; D008561:Membrane Fusion; D008565:Membrane Proteins / Q000378:metabolism*; D009154:Mutation; D006180:Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D050600:SNARE Proteins; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014617:Vacuoles / Q000235:genetics / Q000378:metabolism*; D033921:Vesicular Transport Proteins
chemical_list: C092350:FM 4-64; D005456:Fluorescent Dyes; D008565:Membrane Proteins; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D050600:SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D006180:Proton-Translocating ATPases; D000165:Acridine Orange; D002118:Calcium