Three-dimensional structure of the vacuolar ATPase proton channel by electron microscopy.

Vacuolar ATPases are ATP hydrolysis-driven proton pumps found in the endomembrane system of eucaryotic cells where they are involved in pH regulation. We have determined the three-dimensional structure of the proton channel domain of the vacuolar ATPase from bovine brain clathrin-coated vesicles by electron microscopy at 21 A resolution. The model shows an asymmetric protein ring with two small openings on the luminal side and one large opening on the cytoplasmic side. The central hole on the luminal side is covered by a globular protein, while the cytoplasmic opening is covered by two elongated proteins arranged in a collar-like fashion.