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Published 20 December 2004. doi:10.1083/jcb.200409068
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 167, Number 6, 1087-1098
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Article

Interdependent assembly of specific regulatory lipids and membrane fusion proteins into the vertex ring domain of docked vacuoles



Rutilio A. Fratti, Youngsoo Jun, Alexey J. Merz, Nathan Margolis, and William Wickner

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

Correspondence to Bill Wickner: Bill.Wickner{at}dartmouth.edu

Membrane microdomains are assembled by lipid partitioning (e.g., rafts) or by protein–protein interactions (e.g., coated vesicles). During docking, yeast vacuoles assemble "vertex" ring-shaped microdomains around the periphery of their apposed membranes. Vertices are selectively enriched in the Rab GTPase Ypt7p, the homotypic fusion and vacuole protein sorting complex (HOPS)–VpsC Rab effector complex, SNAREs, and actin. Membrane fusion initiates at vertex microdomains. We now find that the "regulatory lipids" ergosterol, diacylglycerol and 3- and 4-phosphoinositides accumulate at vertices in a mutually interdependent manner. Regulatory lipids are also required for the vertex enrichment of SNAREs, Ypt7p, and HOPS. Conversely, SNAREs and actin regulate phosphatidylinositol 3-phosphate vertex enrichment. Though the PX domain of the SNARE Vam7p has direct affinity for only 3-phosphoinositides, all the regulatory lipids which are needed for vertex assembly affect Vam7p association with vacuoles. Thus, the assembly of the vacuole vertex ring microdomain arises from interdependent lipid and protein partitioning and binding rather than either lipid partitioning or protein interactions alone.

A.J. Merz's current address is Dept. of Biochemistry, University of Washington, Seattle, WA 98195

Abbreviations used in this paper: 3NC, 3-nitrocoumarin; ENTH, epsin NH2-terminal homology domain; HOPS, homotypic fusion and vacuole protein sorting complex; LatB, latrunculin B; MED, MARCKS effector domain; PI, phosphatidylinositol; PI(3)P, PI 3-phosphate; PX, Phox homology.


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