Escherichia coli ATP synthase alpha subunit Arg-376: the catalytic site arginine does not participate in the hydrolysis/synthesis reaction but is required for promotion to the steady state

The three catalytic sites of the F(O)F(1) ATP synthase interact through a cooperative mechanism that is required for the promotion of catalysis. Replacement of the conserved alpha subunit Arg-376 in the Escherichia coli F(1) catalytic site with Ala or Lys resulted in turnover rates of ATP hydrolysis that were 2 x 10(3)-fold lower than that of the wild type. Mutant enzymes catalyzed hydrolysis at a single site with kinetics similar to that of the wild type; however, addition of excess ATP did not chase bound ATP, ADP, or Pi from the catalytic site, indicating that binding of ATP to the second and third sites failed to promote release of products from the first site. Direct monitoring of nucleotide binding in the alphaR376A and alphaR376K mutant F(1) by a tryptophan in place of betaTyr-331 (Weber et al. (1993) J. Biol. Chem. 268, 20126-20133) showed that the catalytic sites of the mutant enzymes, like the wild type, have different affinities and therefore, are structurally asymmetric. These results indicate that alphaArg-376, which is close to the beta- or gamma-phosphate group of bound ADP or ATP, respectively, does not make a significant contribution to the catalytic reaction, but coordination of the arginine to nucleotide filling the low-affinity sites is essential for promotion of rotational catalysis to steady-state turnover.

Beta subunit Glu-185 of Escherichia coli H(+)-ATPase (ATP synthase) is an essential residue for cooperative catalysis

Glu-beta 185 of the Escherichia coli H(+)-ATPase (ATP synthase) beta subunit was replaced by 19 different amino acid residues. The rates of multisite (steady state) catalysis of all the mutant membrane ATPases except Asp- beta 185 were less than 0.2% of the wild type one; the Asp- beta 185 enzyme exhibited 15% (purified) and 16% (membrane-bound) ATPase activity. The purified inactive Cys- beta 185 F1-ATPase recovered substantial activity after treatment with iodoacetate in the presence of MgCl2; maximal activity was obtained upon the introduction of about 3 mol of carboxymethyl residues/mol of F1. The divalent cation dependences of the S-carboxymethyl- beta 185 and Asp- beta 185 ATPase activities were altered from that of the wild type. The Asp- beta 185, Cys- beta 185, S-carboxymethyl-beta 185, and Gln- beta 185 enzymes showed about 130, 60, 20, and 50% of the wild type unisite catalysis rates, respectively. The S-carboxymethyl- beta 185 and Asp- beta 185 enzymes showed altered divalent cation sensitivities, and the S-carboxymethyl- beta 185 enzyme showed no Mg2+ inhibition. Unlike the wild type, the two mutant enzymes showed low sensitivities to azide, which stabilizes the enzyme Mg-ADP complex. These results suggest that Glu- beta 185 may form a Mg2+ binding site, and its carboxyl moiety is essential for catalytic cooperativity. Consistent with this model, the bovine glutamate residue corresponding to Glu- beta 185 is located close to the catalytic site in the higher order structure (Abrahams, J.P., Leslie, A.G.W., Lutter, R ., and Walker, J.E. (1994) Nature 370, 621-628)