Cooperative three-step motions in catalytic subunits of F1-ATPase correlate with 80° and 40° substep rotations

Abstract

Rotation of the central shaft gamma subunit in a molecular motor F(1)-ATPase is assumed to correlate with and probably be driven by domain motions of the three catalytic beta subunits. Here we observe directly these beta motions through an attached fluorophore, concomitantly with 80 degrees and 40 degrees substep rotations of gamma in the same single molecules. We show the sequence of conformations that each beta subunit undergoes in three-step bending, a approximately 40 degrees counterclockwise turn followed by two approximately 20 degrees clockwise turns, occurring in synchronization with two substep rotations of gamma. The results indicate that most previous crystal structures mimic the conformational set of three beta subunits in the catalytic dwells. Moreover, a previously undescribed set of beta conformations, open, closed and partially closed, is revealed in the ATP-waiting dwells. The present study thus bridges the gap between the chemical and mechanical steps in F(1)-ATPase.