Interactions among γR268, γQ269, and the β Subunit Catch Loop of Escherichia coli F1-ATPase Are Important for Catalytic Activity

Abstract

Removal of the ability to form a salt bridge or hydrogen bonds between the β subunit catch loop (βY297-D305) and the γ subunit of Escherichia coli F1Fo-ATP synthase significantly altered the ability of the enzyme to hydrolyze ATP and the bacteria to grow via oxidative phosphorylation. Residues βT304, βD305, βD302, γQ269 and γR268 were found to be very important for ATP hydrolysis catalyzed by soluble F1-ATPase, and the latter four residues were also very important for oxidative phosphorylation. The greatest effects on catalytic activity were observed by the substitution of side chains that contribute to the shortest and/or multiple H-bonds as well as the salt bridge. Residue βD305 would not tolerate substitution with Val or Ser and had extremely low activity as βD305E, suggesting that this residue is particularly important for synthesis and hydrolysis activity. These results provide evidence that tight winding of the γ subunit coiled-coil is important to the rate-limiting step in ATP hydrolysis and are consistent with an escapement mechanism for ATP synthesis in which αβγ intersubunit interactions provide a means to make substrate binding a prerequisite of proton gradient-driven γ subunit rotation.