Mechanical modulation of catalytic power on F1-ATPase

Abstract

The conformational fluctuation of enzymes has a crucial role in reaction acceleration. However, the contribution to catalysis enhancement of individual substates with conformations far from the average conformation remains unclear. We studied the catalytic power of the rotary molecular motor F(1)-ATPase from thermophilic Bacillus PS3 as it was stalled in transient conformations far from a stable pausing angle. The rate constants of ATP binding and hydrolysis were determined as functions of the rotary angle. Both rates exponentially increase with rotation, revealing the molecular basis of positive cooperativity among three catalytic sites: elementary reaction steps are accelerated via the mechanical rotation driven by other reactions on neighboring catalytic sites. The rate enhancement induced by ATP binding upon rotation was greater than that brought about by hydrolysis, suggesting that the ATP binding step contributes more to torque generation than does the hydrolysis step. Additionally, 9% of the ATP-driven rotary step was supported by thermal diffusion, suggesting that acceleration of the ATP docking process occurs via thermally agitated conformational fluctuations.