A Potential Rotational Mechanism of the γ-Subunit of F1 - ATPase--Torque Generation through the Random Movement of an Asymmetric Rotor

Abstract

The rotation of the γ-subunit of F1-ATPase is stochastic, processive, unidirectional, reversible through an external torque, and stepwise with a slow rotation. We propose a novel mechanism that can be applied to explain these properties of the rotary molecular motor, and to determine the direction of rotation. The asymmetric structures of the γ-subunit, both at the tip of the shaft (C- and N-termini) and at the part (e subunit) protruded from the α3β3 subunits, are critical. The torque required for stochastic rotation regarding the center of mass is generated from the impulsive reactive force resulting the random collision between the γ-subunit and the quasihexagonal α3β3 subunits. The rotation is a genuine motion of the confined γ-subunit caused by the asymmetric structure and random motion of the γ-subunit. The steps originate from the chemical reactions of the γ-subunit and physical interaction between the γ-subunit and the flexible protrusions of the α3β3 subunits. An external torque as well as a configurational modification in the γ-subunit (the central rotor) can reverse the rotational direction. We demonstrate the applicability of the novel mechanism to a macroscopic simulation system, which has the essential ingredients of the F1-ATPase structure, by reproducing the dynamic properties of the rotation.