Structure and regulation of the vacuolar ATPases

The vacuolar (H+)-ATPases (V-ATPases) are ATP-dependent proton pumps responsible for both acidification of intracellular compartments and, for certain cell types, proton transport across the plasma membrane. Intracellular V-ATPases function in both endocytic and intracellular membrane traffic, processing and degradation of macromolecules in secretory and digestive compartments, coupled transport of small molecules such as neurotransmitters and ATP and in the entry of pathogenic agents, including envelope viruses and bacterial toxins. V-ATPases are present in the plasma membrane of renal cells, osteoclasts, macrophages, epididymal cells and certain tumor cells where they are important for urinary acidification, bone resorption, pH homeostasis, sperm maturation and tumor cell invasion, respectively. The V-ATPases are composed of a peripheral domain (V1) that carries out ATP hydrolysis and an integral domain (V0) responsible for proton transport. V1 contains eight subunits (A-H) while V0 contains six subunits (a, c, c′, c″, d and e). V-ATPases operate by a rotary mechanism in which ATP hydrolysis within V1 drives rotation of a central rotary domain, that includes a ring of proteolipid subunits (c, c′ and c″), relative to the remainder of the complex. Rotation of the proteolipid ring relative to subunit a within V0 drives active transport of protons across the membrane. Two important mechanisms of regulating V-ATPase activity in vivo are reversible dissociation of the V1 and V0 domains and changes in coupling efficiency of proton transport and ATP hydrolysis. This review focuses on recent advances in our lab in understanding the structure and regulation of the V-ATPases.