Molecular mechanism and robustness of rotary catalysis of F1-ATPase

F1-ATPase is a rotary motor protein in which the inner subunit rotates against the surrounding stator ring upon ATP hydrolysis(1,2). The stator ring is composed of 3 alpha and 3 beta subunits, and the catalytic reaction centers are located on the 3 alpha-beta interfaces, mainly on the beta subunits. The unique feature of F1-ATPase that discriminates it from other molecular motors is the high energy conversion efficiency and the reversibility of the chemomechanical coupling; when the rotation is forcibly reversed, F1-ATPase catalyzes ATP synthesis reaction against large free energy of ATP hydrolysis (3). The experimental verification that the rotary angle of the rotary shaft controls the chemical equilibrium of ATP hydrolysis/synthesis was thought to suggest that the 3 reaction centers communicate via the atomically fine-tuned molecular interaction of the beta subunits with the rotary shaft subunit. However, recent experiments showed the rotation mechanism is far more robust than we though before; even after removing the rotary shaft, the remaining stator ring undergoes cooperative power stroke motion among 3 beta subunits (4). This finding suggests that the allostery is programmed in the stator ring, pointing the possibility that an artificial rod-shaped molecule would be rotated in the stator ring of F1-ATPase. We tested this hypothesis by incorporating a xenogeneic protein in the stator ring. The artificial molecule showed unidirectional rotation although the generated torque is evidently lower than the wild-type F1-ATPase(5).

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5. Baba, M., Iwamoto, K., Iino, R., Ueno, H., Hara, M., Nakanishi, A., Kishikawa, J. I., Noji, H., and Yokoyama, K. (2016) Rotation of artificial rotor axles in rotary molecular motors. Proceedings of the National Academy of Sciences of the United States of America 113, 11214-11219