title: The cDNA sequence of the 69-kDa subunit of the carrot vacuolar H+-ATPase. Homology to the beta-chain of F0F1-ATPases.
abstract: Vacuolar ATPases constitute a novel class of N-ethylmaleimide- and nitrate-sensitive proton pumps associated with the endomembrane system of eukaryotic cells. They resemble F0F1-ATPases in that they are large multimeric proteins, 400-500 kDa, composed of three to nine different subunits. Previous studies have indicated that the active site is located on the approximately 70-kDa subunit. Using antibodies to the approximately 70-kDa subunit of corn to screen a carrot root lambda gt11 cDNA library, we have isolated cDNA clones of the carrot 69-kDa subunit. The complete primary structure of the 69-kDa subunit was then determined from the nucleotide sequence of its cDNA. The 69-kDa subunit consists of 623 amino acids (Mr 68,835), with no obvious membrane-spanning regions. The carrot cDNA sequence was over 70% homologous with exons of a Neurospora 69-kDa genomic clone. The protein sequence of the carrot 69-kDa subunit also exhibited 34.3% identity to four representative F0F1-ATPase beta-chains over a 275-amino-acid core stretch of similar sequence. Alignment studies revealed several regions which were highly homologous to beta-chains, including sequences previously implicated in catalytic function. This provides definitive evidence that the vacuolar ATPase is closely related to the F0F1-type ATPases. A major functional difference between the 69-kDa and beta-subunits is the location of 3 critical cysteine residues: two in the putative catalytic region (Cys-248 and Cys-256) and one in the proposed Mg2+-binding site (Cys-279). These cysteines (and two others) probably account for the sensitivity of the vacuolar H+-ATPase to the sulfhydryl reagent, N-ethylmaleimide. It is proposed that the two ATPases may have arisen from a common ancestor by the insertion or deletion of a large stretch of nonhomologous sequence near the amino-terminal end of the subunit.
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D004247:DNA / Q000235:genetics* / Q000302:isolation & purification; D004262:DNA Restriction Enzymes; D005796:Genes; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009710:Nucleotide Mapping; D009940:Organoids / Q000201:enzymology*; D010944:Plants / Q000201:enzymology / Q000235:genetics*; D006180:Proton-Translocating ATPases / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D014617:Vacuoles / Q000201:enzymology*
chemical_list: D046911:Macromolecular Substances; D004247:DNA; D004262:DNA Restriction Enzymes; D006180:Proton-Translocating ATPases