A model for the cooperative free energy transduction and kinetics of ATP hydrolysis by F1-ATPase.

Abstract

Although the binding change mechanism of rotary catalysis by which F1-ATPase hydrolyzes ATP has been supported by equilibrium, kinetic, and structural observations, many questions concerning the function remain unanswered. Because of the importance of this enzyme, the search for a full understanding of its mechanism is a key problem in structural biology. Making use of the results of free energy simulations and experimental binding constant measurements, a model is developed for the free energy change during the hydrolysis cycle. This model makes possible the development of a kinetic scheme for ATP hydrolysis by F1-ATPase, in which the rate constants are associated with specific configurations of the beta subunits. An essential new element is that the strong binding site for ADP,Pi is shown to be the betaDP site, in contrast to the strong binding site for ATP, which is betaTP. This result provides a rationale for the rotation of the gamma subunit, which induces the cooperativity required for a tri-site binding change mechanism. The model explains a series of experimental data, including the ATP concentration dependence of the rate of hydrolysis and catalytic site occupation for both the Escherichia coli F1-ATPase (EcF1) and Thermophilic Bacillus PS3 F1-ATPase (TF1), which have different behavior.