Plasma membrane proton ATPase Pma1p requires raft association for surface delivery in yeast

Correct sorting of proteins is essential to generate and maintain the identity and function of the different cellular compartments. In this study we demonstrate the role of lipid rafts in biosynthetic delivery of Pma1p, the major plasma membrane proton ATPase, to the cell surface. Disruption of rafts led to mistargeting of Pma1p to the vacuole. Conversely, Pma1-7, an ATPase mutant that is mistargeted to the vacuole, was shown to exhibit impaired raft association. One of the previously identified suppressors, multicopy AST1, not only restored surface delivery but also raft association of Pma1-7. Ast1p, which is a peripheral membrane protein, was found to directly interact with Pma1p inducing its clustering into a SDS/Triton X100-resistant oligomer. We suggest that clustering facilitates partition of Pma1p into rafts and transport to the cell surface.