H(+)-ATPase gamma subunit of Escherichia coli. Role of the conserved carboxyl-terminal region

Abstract

Cloned uncG genes (wild-type or in vitro mutagenized) for the Escherichia coli gamma subunit were introduced into the uncG mutant Gln-14----end), and the functions of the mutant subunits were studied. The F1's with Ala-283----end and Thr-277----end mutant gamma subunits had 63 and 14% of the wild-type ATPase activity, respectively, and mutants with these subunits showed reduced growth by oxidative phosphorylation, indicating that the 10 residues at the carboxyl terminus (286th residue) are important, but dispensable, for catalysis. On the other hand, F1 with a Gln-269----end gamma subunit was inactive. Replacement of conserved residues (Gln-269, Thr-273, or Glu-275) between Gln-269 and Leu-276 gave enzymes with significantly reduced ATPase activity (2-41% of that of the wild-type) and lower ATP-driven proton conduction. Thus these residues are required for the normal catalytic activity of F1, although they are not absolutely essential. Membranes with amino acid replacements (Thr-277----end, Gln-269----Leu, or Glu-275----Lys) and the frameshift mutation (downstream of Thr-277) had about 15% of the wild-type ATPase activity, but showed different degrees of ATP-dependent H+ translocation and growth yield by oxidative phosphorylation, suggesting that the gamma subunit, especially its carboxyl-terminal region, functions in coupling between catalysis and H+ translocation.