Vacuolar H⁺-translocating ATPases from plants: Structure, function, and isoforms

The vacuolar H⁺-translocating ATPase (V-type ATPase) plays a central role in the growth and development of plant cells. In a mature cell, the vacuole is the largest intracellular compartment, occupying about 90% of the cell volume. The proton electrochemical gradient (acid inside) formed by the vacuolar ATPase provides the primary driving force for the transport of numerous ions and metabolites against their electrochemical gradients. The uptake and release of solutes across the vacuolar membrane is fundamental to many cellular processes, such as osmoregulation, signal transduction, and metabolic regulation. Vacuolar ATPases may also reside on endomembranes, such as Golgi and coated vesicles, and thus may participate in intracellular membrane traffic, sorting, and secretion. Plant vacuolar ATPases are large complexes (400-650 kDa) composed of 7-10 different subunits. The peripheral sector of 5-6 subunits includes the nucleotide-binding catalytic and regulatory subunits of ∼ 70 and ∼ 60 kDa, respectively. Six copies of the 16-kDa proteolipid together with 1-3 other subunits make up the integral sector that forms the H⁺ conducting pathway. Isoforms of plant vacuolar ATPases are suggested by the variations in subunit composition observed among and within plant species, and by the presence of a small multigene family encoding the 16-kDa and 70-kDa subunits. Multiple genes may encode isoforms with specific properties required to serve the diverse functions of vacuoles and endomembrane compartments.