Domains near ATP gamma phosphate in the catalytic site of H+-ATPase. Model proposed from mutagenesis and inhibitor studies

Abstract

The beta Gly-149 residue is in a glycine-rich sequence (Gly-Gly-Ala-Gly-Val-Gly-Lys-Thr; residues 149-156) of the Escherichia coli H(+)-ATPase (ATP synthase) beta subunit. Substitution of beta Gly-149 by Ser suppressed the effect of the beta Ser-174-->Phe mutation (Iwamoto, A., Omote, H., Hanada, H., Tomioka, N., Itai, A., Maeda, M., and Futai, M. (1991) J. Biol. Chem. 266, 16350-16355), suggesting that beta Gly-149 is located near beta Ser-174. In this study, we introduced different residues at position 149 and found that a single mutant beta Cys-149 was defective. The effect of beta Cys-149 mutation was suppressed by beta Gly-172-->Glu, beta Ser-174-->Phe, beta Glu-192-->Val, or beta Val-198-->Ala replacement. These results suggest that beta Gly-149, beta Gly-172, beta Ser-174, beta Glu-192, and beta Val-198 residues are located close together in the catalytic site. From these findings we propose a model of the catalytic site of the enzyme near the gamma phosphate moiety of ATP. F1 enzymes with the double mutations beta Cys-149/beta Glu-172, beta Cys-149/beta Phe-174, beta Cys-149/beta Val-192, and beta Cys-149/beta Ala-198 were less sensitive than wild-type F1 to dicyclohexylcarbodiimide and adenosine triphosphopyridoxal (an affinity analogue of ATP forming a Schiff base with the epsilon-amino group of beta Lys-155 or beta Lys-201), and became sensitive to N-ethylmaleimide in an ATP-protected manner. These results of inhibitor studies are consistent with the proposed model.