Cell Biology and Evolution of Proton Pumps

Abstract

The vacuolar system of eukaryotic cells contains a large number of organelles that are primarily energized by an H⁺-ATPase that was named V-ATPase. Several genes encoding subunits of the enzyme were cloned and sequenced. The sequence information revealed the relations between V-ATPases and F-ATPases that evolved from common ancestral genes. Genes encoding subunits of V-ATPase in yeast cells were interrupted to yield mutants that are devoid of the enzyme and are sensitive to pH and calcium concentrations in the medium. The mutants were used for the study of structure, function, molecular biology and biogenesis of the V-ATPase. The function of V-ATPases in energizing the vacuolar system of eukaryotes is discussed.

cDNA cloning of 12 subunits of the V-type ATPase from Mesembryanthemum crystallinum and their expression under stress

“…A rather small rotor (probably B/100 kDa) consisting of a ring of VHA-c subunits within the membrane and a central stalk extending to the cytoplasm rotates in a stator structure which is composed of a hexameric head, membraneassociated subunits and peripheric connectors. Electron microscopic analyses and X-ray deflection studies of increasing resolution as well as the identification and sequencing of the V-ATPase subunits have proven that despite the similar basic structure, the conserved enzymatic mechanism and the common ancestor (Nelson et al 1995), V-ATPase, archaea ATPase and F-ATP synthase have specific functional and regulatory features and distinct structural components (Perzov et al 2001).…”

Electrochemical cells from water ice? Preliminary methods and results

“…It allows for a pH gradient across the membrane that can be used for biological processes. There are a number of different mechanisms/types of proton pumps, and these have evolved several times within living organisms independently [25]. Modest production of electricity via the action of pH gradients in ice may be important for studies about the PLOS ONE origin of life in icy worlds, as they provide a pathway for abiogenesis.…”

Mutants of Saccharomyces cerevisiae defective in vacuolar function confirm a role for the vacuole in toxic metal ion detoxification

“…Compartmentalisation of these toxic metals in the vacuole may prevent the accumulation of potentially toxic metal cations in the cytosol and resultant toxic effects [2, 3, 10, 14, 15]. Transport of these metal cations across the vacuolar membrane has been shown to occur by cation‐proton exchange driven by the vacuolar trans‐membrane electrochemical pH gradient which is energised by the vacuolar H + ‐ATPase (V‐ATPase) [7, 11, 16, 17]. Although a link between vacuolar compartmentalisation and metal tolerance is frequently cited for those potentially toxic metals preferentially localised in the vacuole, most supporting data are indirect.…”

“…Three mutants were from a set isolated on the basis of deficient targeting of vacuolar proteins to the vacuole (vpt, vacuolar targeting mutant). Mutant JSR18Δ1 is devoid of any vacuole‐like structure and can thus be used as a model for vacuole‐lacking yeast cells[19] while ScVatB and ScVatC are deficient in a specific protein subunit of the V‐ATPase resulting in no acidification of the vacuole [17, 20]. ScVatB lacks the B subunits of the catalytic sector and ScVatC lacks the c (proteolipid) subunits of the membrane sector of the V‐ATPase[21].…”