Nucleotide Exchange Mechanism Involving Angle-Dependent Rate Constants Extracted from F1-ATPase Single-Molecule Rotation Trajectories

Evidence has been mounting that in the rotational cycle of F1-ATPase there is a concerted ATP binding and ADP release that yields a million-fold acceleration in the rate of the product ADP release. We developed a theory of reaction kinetics to investigate the relationship between the concerted nucleotide exchange and previous single-molecule forced rotation data from Adachi, K. <i>Nat. Commun.</i> 2012, 3, 1022. We extracted from these data angle-dependent rate constants for nucleotide binding and release. The rate constants were then used in a unified kinetic scheme, also consistent with other single-molecule and ensemble experiments, to obtain analytical equations for nucleotide occupancy change events from nano- to millimolar ATP concentrations. A theory-experiment comparison revealed novel evidence about the concerted mechanism: it is determined by correlated conformational changes in the F1-ATPase ring, and its kinetic signature is a unified angle-dependent function of the nucleotide binding and release rate constants, which is independent of ATP concentration.