Structure, function and regulation of the vacuolar (H+)-ATPases

The vacuolar (H+)-ATPases (or V-ATPases) function to acidify intracellular compartments in eukaryotic cells, playing an important role in such processes as receptor-mediated endocytosis, intracellular membrane traffic, protein degradation and coupled transport, V-ATPases in the plasma membrane of specialized cells also function in renal acidification, bone resorption and cytosolic DPI maintenance. The V-ATPases are composed of two domains. The VI domain is a 570-kDa peripheral complex composed of 8 subunits (subunits A-H) of molecular weight 70-13 kDa which is responsible for ATP hydrolysis. The V-0 domain is a 260-kDa integral complex composed of 5 submits (subunits a-d) which is responsible for proton translocation, The V-ATPases are structurally related to the F-ATPases which function in ATP synthesis. Biochemical and mutational studies have begun to reveal the function of individual subunits and residues in V-ATPase activity. A central question in this field is the mechanism of regulation of vacuolar acidification in vivo. Evidence has been obtained suggesting a number of possible mechanisms of regulating V-ATPase activity, including reversible dissociation of V-1 and V-0 domains, disulfide bond formation at the catalytic site and differential targeting of V-ATPases, Control of anion conductance may also function to regulate vacuolar pH, Because of the diversity of functions of V-ATPases, cells most likely employ multiple mechanisms for controlling their activity, (C) 1998 Federation of European Biochemical Societies.