Vacuole membrane fusion: V0 functions after trans-SNARE pairing and is coupled to the XXXX -releasing channel.

@entity141 @entity375 @entity11858
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 @entity375 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 @entity11858 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 @entity141 , but they did not fuse. The @entity141 -releasing channel appears to be tightly coupled to V0 because inactivation of @entity11858 by antibodies blocked @entity141 release. @entity11858 deletion on only one fusion partner sufficed to severely reduce fusion activity. The functional requirement for @entity11858 correlates to V0 transcomplex formation in that both occur after docking and @entity141 release. These observations establish V0 as a crucial factor in vacuole fusion acting downstream of trans-SNARE pairing.
