Evidence that the NH2 terminus of Vph1p, an integral subunit of the V0 sector of the yeast V-ATPase, interacts directly with the Vma1p and Vma13p subunits of the V1 sector

The vacuolar-type H+-ATPase (V-ATPase) is composed of a peripherally bound (V-1) and a membrane-associated (V-0) complex. V-1 ATP hydrolysis is thought to rotate a central stalk, which in turn, is hypothesized to drive V-0 proton translocation. Transduction of torque exerted by the rotating stalk on V-0 requires a fixed structural link (stator) between the complexes to prevent energy loss through futile rotation of V-1 relative to V-0; this work sought to identify stator components. The 95-kDa V-ATPase subunit, Vph1p, has a cytosolic NH2 terminus (Nt-Vph1p) and a membrane-associated COOH terminus. Two-hybrid assays demonstrated that Nt-Vph1p interacts with the catalytic V-1 subunit, Vma1p. Co-immunoprecipitation of Vma1p with Nt-Vph1p confirmed the interaction. Expression of Nt-Vph1p in a Delta vph1 mutant was necessary to recruit Vma13p to V-1. Vma13p bound to Nt-Vph1p in vitro demonstrating direct interaction. Limited trypsin digests cleaves both Nt-Vph1p and Vma13p. The same tryptic treatment results in a loss of proton translocation while not reducing bafilomycin A(1)-sensitive ATP hydrolysis, Trypsin cleaved Vph1p at arginine 53. Elimination of the tryptic cleavage site by substitution of arginine 53 to serine partially protected vacuolar acidification from trypsin digestion. These results suggest that Vph1p may function as a component of a fixed structural link, or stator, coupling V-1 ATP hydrolysis to V-0 proton translocation.