TitleExcess vacuolar SNAREs drive lysis and Rab bypass fusion.
Publication TypeJournal Article
Year of Publication2007
AuthorsStarai, VJ, Jun, Y, Wickner, W
JournalProc Natl Acad Sci U S A
Volume104
Issue34
Pagination13551-8
Date Published2007 Aug 21
ISSN0027-8424
KeywordsKinetics, Membrane Fusion, Protein Binding, rab GTP-Binding Proteins, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins, SNARE Proteins, Solubility, Vacuoles
Abstract

Although concentrated soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) drive liposome fusion and lysis, the fusion of intracellular membranes also requires Rab GTPases, Rab effectors, SM proteins, and specific regulatory lipids and is accompanied by little or no lysis. To rationalize these findings, we generated yeast strains that overexpress all four vacuolar SNAREs (4SNARE(++)). Although vacuoles with physiological levels of Rab, Rab effector/SM complex, and SNAREs support rapid fusion without Rab- and SNARE-dependent lysis, vacuoles from 4SNARE(++) strains show extensive lysis and a reduced need for the Rab Ypt7p or regulatory lipids for fusion. SNARE overexpression and the addition of pure homotypic fusion and vacuole protein sorting complex (HOPS), which bears the vacuolar SM protein, enables ypt7Delta vacuoles to fuse, allowing direct comparison of Rab-dependent and Rab-independent fusion. Because 3- to 40-fold more of each of the five components that form the SNARE/HOPS fusion complex are required for vacuoles from ypt7Delta strains to fuse at the same rate as vacuoles from wild-type strains, the apparent forward rate constant of 4SNARE/HOPS complex assembly is enhanced many thousand-fold by Ypt7p. Rabs function in normal membrane fusion by concentrating SNAREs, other proteins (e.g., SM), and key lipids at a fusion site and activating them for fusion without lysis.

DOI10.1073/pnas.0704741104
Alternate JournalProc. Natl. Acad. Sci. U.S.A.
PubMed ID17699614
Department Authors: 
Vincent J. Starai
Lab Association: 
Starai
Research Areas: 
Molecular Microbiology
Microbial Physiology