V ATPases are multimeric proton-pumps. The 100 kDa 'a' subunit is encoded by four isoforms (a1-a4) in mammals and two (Vph1p and Stv1p) in yeast. a3 is enriched in osteoclasts and essential for bone resorption while a4 is expressed in the distal nephron and acidifies urine. Mutations in human a3 and a4 result in osteopetrosis and distal renal tubular acidosis, respectively. Human a3 (G405R, R444L) and a4 (P524L, G820R) mutations were recreated in the yeast ortholog Vph1p: a3 (G424R, R462L), a4 (W520L, G812R). Mutations in a3 resulted in wild-type vacuolar acidification and growth on media containing 4 mM ZnCl2, 200 mM CaCl2, or buffered to pH 7.5 with V ATPase hydrolytic and pumping activity decreased by 30-35%. Immunoblots confirmed wild-type levels for V ATPase a, A and B subunits on vacuolar membranes. a4 G812R resulted in defective growth on selective media with V ATPase hydrolytic and pumping activity decreased by 83-85% yet with wild-type levels of 'a', A, and B subunits on vacuolar membranes. The a4 W520L mutation had defective growth on selective media with no detectable V ATPase activity and reduced expression of 'a', A, and B subunits. The a4 W520L mutation phenotypes were dominant-negative, as overexpression of wild-type yeast 'a' isoforms, Vph1p, or Stv1p, did not restore growth. However, deletion of endoplasmic reticulum assembly factors (Vma12p, Vma21p, Vma22p) partially restored 'a' and B expression. That a4 W520L affects both Vo and V1 subunits is a unique phenotype for any V ATPase subunit mutation and supports the concerted pathway for V ATPase assembly in vivo.
|Evidence ID||Analyze ID||Interactor||Interactor Systematic Name||Interactor||Interactor Systematic Name||Type||Assay||Annotation||Action||Modification||Phenotype||Source||Reference||Note|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Gene Ontology Term||Gene Ontology Term ID||Qualifier||Aspect||Method||Evidence||Source||Assigned On||Reference||Annotation Extension|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Phenotype||Experiment Type||Experiment Type Category||Mutant Information||Strain Background||Chemical||Details||Reference|
|Evidence ID||Analyze ID||Regulator||Regulator Systematic Name||Target||Target Systematic Name||Experiment||Conditions||Strain||Source||Reference|