Vacuolar and Plasma Membrane Proton-Adenosinetriphosphatases

Abstract

The vacuolar H+-ATPase (V-ATPase) is one of the most fundamental enzymes in nature. It functions in almost every eukaryotic cell and energizes a wide variety of organelles and membranes. V-ATPases have similar structure and mechanism of action with F-ATPase and several of their subunits evolved from common ancestors. In eukaryotic cells, F-ATPases are confined to the semi-autonomous organelles, chloroplasts, and mitochondria, which contain their own genes that encode some of the F-ATPase subunits. In contrast to F-ATPases, whose primary function in eukaryotic cells is to form ATP at the expense of the proton-motive force (pmf), V-ATPases function exclusively as ATP-dependent proton pumps. The pmf generated by V-ATPases in organelles and membranes of eukaryotic cells is utilized as a driving force for numerous secondary transport processes. The mechanistic and structural relations between the two enzymes prompted us to suggest similar functional units in V-ATPase as was proposed to F-ATPase and to assign some of the V-ATPase subunit to one of four parts of a mechanochemical machine: a catalytic unit, a shaft, a hook, and a proton turbine. It was the yeast genetics that allowed the identification of special properties of individual subunits and the discovery of factors that are involved in the enzyme biogenesis and assembly. The V-ATPases play a major role as energizers of animal plasma membranes, especially apical plasma membranes of epithelial cells. This role was first recognized in plasma membranes of lepidopteran midgut and vertebrate kidney. The list of animals with plasma membranes that are energized by V-ATPases now includes members of most, if not all, animal phyla. This includes the classical Na+ absorption by frog skin, male fertility through acidification of the sperm acrosome and the male reproductive tract, bone resorption by mammalian osteoclasts, and regulation of eye pressure. V-ATPase may function in Na+ uptake by trout gills and energizes water secretion by contractile vacuoles in Dictyostelium. V-ATPase was first detected in organelles connected with the vacuolar system. It is the main if not the only primary energy source for numerous transport systems in these organelles. The driving force for the accumulation of neurotransmitters into synaptic vesicles is pmf generated by V-ATPase. The acidification of lysosomes, which are required for the proper function of most of their enzymes, is provided by V-ATPase. The enzyme is also vital for the proper function of endosomes and the Golgi apparatus. In contrast to yeast vacuoles that maintain an internal pH of ∼5.5, it is believed that the vacuoles of lemon fruit may have a pH as low as 2. Similarly, some brown and red alga maintain internal pH as low as 0.1 in their vacuoles. One of the outstanding questions in the field is how such a conserved enzyme as the V-ATPase can fulfill such diverse functions.

Regulated acid–base transport in the collecting duct

“…V-type H + -ATPases are multi-subunit protein complex consisting of at least 14 subunits in humans (for a detailed review on H + -ATPase structure, function, and regulation, see recent reviews: (54,55,119,122,202)). Most subunits occur in different isoforms that may be specific to organs, cell types, or subcellular organelles.…”

PDE1 Encodes a P-Type ATPase Involved in Appressorium-Mediated Plant Infection by the Rice Blast Fungus Magnaporthe grisea

“…P-type ATPases are so named because of the phosphoenzyme intermediate formed during their activation and have been implicated in a number of transport and signaling processes. The best-known members of the group are H ϩ -ATPases and heavy metal transporters (for reviews, see Catty et al, 1997;Bevers et al, 1999;Nelson and Harvey, 1999). All P-type ATPases share a core structure, including the presence of a phosphorylation site, an ATP binding domain, and three other consensus sequences ( Figure 5).…”

Quantal transmitter release by glioma cells: quantification of intramembrane particle changes

“…Also, transfection of neuroblastoma N18-TG-2 cells with mediatophore cDNA induced both a Ca 2þ -dependent and quantal ACh release (Falk-Vairant et al, 1996a;, and a transient increase of medium and large IMPs , as summarised in Table 1. The 15-kDa proteolipid forming mediatophore is implicated in several cellular processes. It is a component of the membrane sector of V-ATPase (Nelson and Harvey, 1999); it was found in invertebrate gap junctions (Finbow and Pitts, 1998) and was recently identi¢ed in the yeast as the Ca 2þ -sensitive proteolipid involved in membrane fusion (Peters et al, 2001). As suggested by the latter authors, it is possible that the proteolipid rings of 15-kDa subunits forming mediatophores expand radially during opening.…”