γM23K, γM232K, and γL77K single substitutions in the TFI-ATPase lower ATPase activity by disrupting a cluster of hydrophobic side chains

In crystal structures of the bovine F-1-ATPase (MF1), the side chains of gammaMet(23), gammaMet(232), and gammaLeu(77) interact in a cluster. Substitution of the corresponding residues in the alpha(3)beta(3)gamma subcomplex of TF1 with lysine lowers the ATPase activity to 2.3, 11, and 15%, respectively, of that displayed by wild-type. In contrast, TF1 subcomplexes containing the gammaM(23)C, gammaM(232)C, and gammaL(77)C substitutions display 36, 36, and 130%, respectively, of the wild-type ATPase activity. The ATPase activity of the gammaM(23)C/gammaM(232)C double mutant subcomplex is 36% that of the wild-type subcomplex before and after cross-linking the introduced cysteines, whereas the ATPase activity of the gammaM(23)C/(LC)-C-77 double mutant increased from 50 to 85% that of wild-type after cross-linking the introduced cysteines. Only beta-beta cross-links formed when the alpha(3)(betaE(395)C)(3)gammaM(23)C double mutant was inactivated with CuCl2. The overall results suggest that the attenuated ATPase of the mutant subcomplexes containing the gammaM(23)K, gammaL(77)K, and gammaM(232)K substitutions is caused by disruption of the cluster of hydrophobic amino acid side chains and that the midregion of the coiled-coil comprised of the amino- and carboxyl-terminal alpha helices of the gamma subunit does not undergo unwinding or major displacement from the side chain of gammaLeu(77) during ATP-driven rotation of the gamma subunit.