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J Biol Chem, Vol. 273, Issue 35, 22292-22297, August 28, 1998

A Mutation in the Escherichia coli F₀F₁-ATP Synthase Rotor, E208K, Perturbs Conformational Coupling between Transport and Catalysis

From the Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia 22906-0011

Cross-linking studies on the Escherichia coli F₀F₁-ATP synthase indicated a site of interaction involving  and  subunits in F₁ and subunit c in F₀ (Watts, S. D., Tang, C., and Capaldi, R. A. (1996) J. Biol. Chem. 271, 28341-28347). To assess the function of these interactions, we introduced random mutations in this region of the  subunit (194-213). One mutation, Glu-208 to Lys (E208K), caused a temperature-sensitive defect in oxidative phosphorylation-dependent growth. ATP hydrolytic rates of the E208K F₀F₁ enzyme became increasingly uncoupled from H⁺ pumping above 28 °C. In contrast, Arrhenius plot of steady-state ATP hydrolysis of the mutant enzyme was linear from 20 to 50 °C. Analysis of this plot revealed a significant increase in the activation energy of the catalytic transition state to a value very similar to soluble,  subunit-inhibited F₁ and suggested that the mutation blocked normal release of  inhibition of ATP hydrolytic activity upon binding of F₁ to F₀. The difference in temperature dependence suggested that the E208K mutation perturbed release of inhibition via a different mechanism than it did energy coupling. Suppressor mutations in the polar loop of subunit c restored ATP-dependent H⁺ pumping and transition state thermodynamic parameters close to wild-type values indicating that interactions between  and c subunits mediate release of  inhibition and communication of coupling information.

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