Vps52p, Vps53p, and Vps54p form a novel multisubunit complex required for protein sorting at the yeast late Golgi

The late Golgi of the yeast Saccharomyces cerevisiae receives membrane traffic from the secretory pathway as well as retrograde traffic from post-Golgi compartments, but the machinery that regulates these vesicle-docking and fusion events has not been characterized. We have identified three components of a novel protein complex that is required for protein sorting at the yeast late Golgi compartment. Mutation of VPS52, VPS53, or VPS54 results in the missorting of 70% of the vacuolar hydrolase carboxypeptidase Y as well as the mislocalization of late Golgi membrane proteins to the vacuole, whereas protein traffic through the early part of the Golgi complex is unaffected. A vps52/53/54 triple mutant strain is phenotypically indistinguishable from each of the single mutants, consistent with the model that all three are required for a common step in membrane transport. Native coimmunoprecipitation experiments indicate that Vps52p, Vps53p, and Vps54p are associated in a 1:1:1 complex that sediments as a single peak on sucrose velocity gradients. This complex, which exists both in a soluble pool and as a peripheral component of a membrane fraction, colocalizes with markers of the yeast late Golgi by immunofluorescence microscopy. Together, the phenotypic and biochemical data suggest that VPS52, VPS53, and VPS54 are required for the retrograde transport of Golgi membrane proteins from an endosomal/prevacuolar compartment. The Vps52/53/54 complex joins a growing list of distinct multisubunit complexes that regulate membrane-trafficking events.