Vacuolar-type ATPase: A proton pump to lysosomal trafficking.

Vacuolar-type ATPase (V-ATPase), initially identified in yeast and plant vacuoles, pumps protons into the lumen of organelles coupled with ATP hydrolysis. The mammalian counterpart is found ubiquitously in endomembrane organelles and the plasma membrane of specialized cells such as osteoclasts. V-ATPase is also present in unique organelles such as insulin secretory granules, neural synaptic vesicles, and acrosomes of spermatozoa. Consistent with its diverse physiological roles and unique localization, the seven subunits of V-ATPase have 2-4 isoforms that are organelle- or cell-specific. Subunits of the enzyme function in trafficking organelles and vesicles by interacting with small molecule GTPases. During osteoclast differentiation, one of the four isoforms of subunit a, a3, is indispensable for secretory lysosome trafficking to the plasma membrane. Diseases such as osteopetrosis, renal acidosis, and hearing loss are related to V-ATPase isoforms. In addition to its role as an enzyme, V-ATPase has versatile physiological roles in eukaryotic cells.