Torque Generation Mechanism of ATP Synthase and Other Rotary Motors

Ion driven rotary motors, including F0-ATP synthase (F0) and the bacterial flagellar motor, convert energy from ion translocation into torque and rotary motion. Here we propose a mechanism whereby electric fields emanating from channels in the stator(s) create forces acting on ion binding sites in the rotor, driving it to rotate. The model predicts a scaling law relating torque to ion motive force and number of stators, consistent with experiment. The rotor of F0 drives the gamma-subunit to rotate within the ATP-producing complex (F1), working against an opposing torque that rises and falls periodically with angular position. Drawing an analogy with the washboard potential of the superconducting Josephson junction, we compute ATP production rate vs. ion motive force, finding excellent quantitative agreement with experiment and accounting for the crossover from ATP production to consumption. Plausible mechanisms for reversing the direction of bacterial flagellar rotation become self-evident in the model. (Supported by NIH R21CA133153, TcSUH, Welch (E-1221), and THECB-ARP.)