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MBC in Press, published online ahead of print April 2, 2008
Mol. Biol. Cell 10.1091/mbc.E08-01-0077

A more recent version of this article appeared on June 1, 2008 Originally published as MBC in Press, 10.1091/mbc.E08-01-0077 on April 16, 2008
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Submitted on January 25, 2008
Revised on March 14, 2008
Accepted on March 20, 2008

HOPS Proofreads the trans-SNARE Complex for Yeast Vacuole Fusion

Vincent J. Starai, Christopher M. Hickey, and William Wickner

Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755

Monitoring Editor: Thomas U. Martin

The fusion of yeast vacuoles, like other organelles, requires a Rab-family GTPase (Ypt7p), a Rab effector and an SM protein (HOPS complex), and SNAREs. The central 0-layer of the 4 bundled vacuolar SNAREs requires the wild-type 3 glutaminyl (Q) and 1 arginyl (R) residues for optimal fusion. Alterations of this layer dramatically increase the Km for SNAREs to assemble trans-SNARE complexes and to fuse. We now find that added purified HOPS complex strongly suppresses the fusion of vacuoles bearing 0-layer alterations, but has little effect on the fusion of vacuoles with wild-type SNAREs. HOPS proofreads at 2 levels, inhibiting the formation of trans-SNARE complexes with altered 0-layers and suppressing the ability of these mismatched 0-layer trans-SNARE complexes to support membrane fusion. HOPS proofreading also extends to other parts of the SNARE complex, as it suppresses the fusion of trans-SNARE complexes formed without the N-terminal PX domain of Vam7p (Qc). Unlike some other SM proteins, HOPS proofreading does not require the Vam3p (Qa) N-terminal domain. HOPS thus proofreads SNARE domain and N-terminal domain structures and regulates the fusion capacity of trans-SNARE complexes, only allowing full function for wild-type SNARE configurations. This is the most direct evidence to date that HOPS is directly involved in the fusion event.

Address correspondence to: William Wickner (Bill.Wickner{at}Dartmouth.edu)






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