title: Defective assembly of a hybrid vacuolar H(+)-ATPase containing the mouse testis-specific E1 isoform and yeast subunits.
abstract: Mammalian vacuolar-type proton pumping ATPases (V-ATPases) are diverse multi-subunit proton pumps. They are formed from membrane V(o) and catalytic V(1) sectors, whose subunits have cell-specific or ubiquitous isoforms. Biochemical study of a unique V-ATPase is difficult because ones with different isoforms are present in the same cell. However, the properties of mouse isoforms can be studied using hybrid V-ATPases formed from the isoforms and other yeast subunits. As shown previously, mouse subunit E isoform E1 (testis-specific) or E2 (ubiquitous) can form active V-ATPases with other subunits of yeast, but E1/yeast hybrid V-ATPase is defective in proton transport at 37 degrees C (Sun-Wada, G.-H., Imai-Senga, Y., Yamamoto, A., Murata, Y., Hirata, T., Wada, Y., and Futai, M., 2002, J. Biol. Chem. 277, 18098-18105). In this study, we have analyzed the properties of E1/yeast hybrid V-ATPase to understand the role of the E subunit. The proton transport by the defective hybrid ATPase was reversibly recovered when incubation temperature of vacuoles or cells was shifted to 30 degrees C. Corresponding to the reversible defect of the hybrid V-ATPase, the V(o) subunit a epitope was exposed to the corresponding antibody at 37 degrees C, but became inaccessible at 30 degrees C. However, the V(1) sector was still associated with V(o) at 37 degrees C, as shown immunochemically. The control yeast V-ATPase was active at 37 degrees C, and its epitope was not accessible to the antibody. Glucose depletion, known to dissociate V(1) from V(o) in yeast, had only a slight effect on the hybrid at acidic pH. The domain between Lys26 and Val83 of E1, which contains eight residues not conserved between E1 and E2, was responsible for the unique properties of the hybrid. These results suggest that subunit E, especially its amino-terminal domain, plays a pertinent role in the assembly of V-ATPase subunits in vacuolar membranes.
authors.affiliation: Department of Biochemistry, Faculty of Pharmaceutical Sciences, Iwate Medical University, Iwate, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Hayashi
authors.forename: Ge-Hong
authors.initials: GH
authors.lastname: Sun-Wada
authors.forename: Yoh
authors.initials: Y
authors.lastname: Wada
authors.forename: Mayumi
authors.initials: M
authors.lastname: Nakanishi-Matsui
authors.forename: Masamitsu
authors.initials: M
authors.lastname: Futai
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D013696:Temperature; D013737:Testis / Q000201:enzymology; D025262:Vacuolar Proton-Translocating ATPases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; C500733:Vma4 protein, S cerevisiae; D025262:Vacuolar Proton-Translocating ATPases; D005947:Glucose