Effects of human a3 and a4 mutations that result in osteopetrosis and distal renal tubular acidosis on yeast V-ATPase expression and activity.
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 is essential for bone resorption, whereas 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 and R444L) and a4 (P524L and G820R) mutations were recreated in the yeast ortholog Vph1p, a3 (G424R and R462L), and a4 (W520L and 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, and 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.
Ochotny
Noelle
N
Department of Pharmacology, University of Toronto, Toronto, Ontario M5G 1G6, Canada.
Van Vliet
Aaron
A
Chan
Nelson
N
Yao
Yeqi
Y
Morel
Mario
M
Kartner
Norbert
N
von Schroeder
Herbert P
HP
Heersche
Johan N M
JN
Manolson
Morris F
MF
D000141:Acidosis, Renal Tubular / Q000201:enzymology / Q000235:genetics; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D004791:Enzyme Inhibitors / Q000378:metabolism; D005838:Genotype; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D018942:Macrolides / Q000378:metabolism; D051379:Mice; D009154:Mutation; D010022:Osteopetrosis / Q000201:enzymology / Q000235:genetics; D010641:Phenotype; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D025262:Vacuolar Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism; D014617:Vacuoles / Q000737:chemistry
D004791:Enzyme Inhibitors; D007527:Isoenzymes; D018942:Macrolides; D021122:Protein Subunits; D029701:Saccharomyces cerevisiae Proteins; C036978:concanamycin A; D000255:Adenosine Triphosphate; D025262:Vacuolar Proton-Translocating ATPases