Vacuolar-type H+-translocating ATPases IN plant endomembranes: subunit organization and multigene families

Abstract

Acidification of endomembrane compartments by the vacuolar-type H+-translocating ATPase (V-ATPase) is vital to the growth and development of plants. The V-ATPase purified from oat roots is a large complex of 650×10Mr that contains 10 different subunits of 70, 60,44,42, 36, 32, 29, 16, 13 and 12 × 103Mr. This set of ten polypeptides is sufficient to couple ATP hydrolysis to proton pumping after reconstitution of the ATPase into liposomes. Unlike some animal V-ATPases, the purified and reconstituted V-ATPase from oat is directly stimulated by Cl−. The peripheral complex of the ATPase includes the nucleotide-binding subunits of 70 and 60 × 103Mr and polypeptides of 44, 42, 36 and 29 × 103Mr. Six copies of the 16 × 103Mr proteolipid together with three other polypeptides are thought to make up the integral sector that forms the H+-conducting pathway. Release of the peripheral complex from the native membrane completely inactivates the pump; however, the peripheral subunits can be reassembled with the membrane sector to form a functional H+ pump.Comparison of V-ATPases from several plants indicates considerable variations in subunit composition. Hence, several forms of the V-ATPase may exist among, and probably within, plant species. At least four distinct cDNAs encode the 16 × 103Mr proteolipid subunit in oat. Multiple genes could encode different subtypes of the H+ pump that are regulated by the developmental stage and physiological function specific to the cell or tissue type.