Structural features and nucleotide-binding capability of the C subunit are integral to the regulation of the eukaryotic V₁V₀ ATPases

V-ATPases (vacuolar ATPases) are responsible for acidification of intracellular compartments and, in certain cases, proton transport across the plasma membrane of eukaryotic cells. They are composed of a catalytic V ₁ sector, in which ATP hydrolysis takes place, and the V₀ sector, which functions in proton conduction. The best established mechanism for regulating the V-ATPase activity in vivo involves reversible dissociation of the V₁ and V₀ domains, in which subunit C is intimately involved. In the last year, impressive progress has been made in elucidating the structure of the C subunit and its arrangement inside the V-ATPase. Nucleotide occupancy by subunit C, followed by conformational changes of this subunit has shed light on the mechanism of V-ATPase regulation.