Xu H and Wickner W (2006) Bem1p is a positive regulator of the homotypic fusion of yeast vacuoles. J Biol Chem 281(37):27158-66
Abstract: Docked vacuoles are believed to undergo rapid lipid mixing during hemifusion, then a slow, rate-limiting completion of fusion and mixing of lumenal contents. Previous genomic analysis has suggested that Bem1p, a scaffold protein critical for cell polarity, may support vacuole fusion. We now report that bem1 strains have fragmented vacuoles (vps class B and C). During in vitro fusion reactions, vacuoles from bem1 strains showed a strong reduction in the rate of lipid mixing when compared to vacuoles from the BEM1 parent. The reduction in the overall rate of fusion with bem1 vacuoles was modest, consistent with lipid mixing as a non-rate limiting step in the pathway. Though the fusion of either BEM1 (wild-type) or bem1 vacuoles is stimulated by recombinant Bem1p, the lipid mixing of docked bem1 vacuoles is highly dependent on rBem1p under certain reaction conditions. Bem1p-stimulated lipid mixing is blocked by well characterized fusion inhibitors including lipid ligands and antibodies to Ypt7p, Vps33p and Vam3p. Although full-length Bem1p is required for maximal stimulation, a truncation mutant comprising the SH3 domains and the PX domain retains modest stimulatory activity. In contrast to an earlier report, we do not find phosphorylation of Bem1p at Ser 72 to be required for Bem1p-stimulated fusion. Taken together, Bem1p is a positive regulator of lipid mixing during vacuole hemifusion and fusion.
|Status: Published||Type: Journal Article||PubMed ID: 16854988|
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