Mechanism of biological multi-fuel engine

Yasutaka Nishihara and Akio Kitao
Proc. Natl. Acad. Sci., U.S.A. 112, 7737-7742 (2015).

Open access article

The bacterial flagellum is a molecular machine for the locomotion of bacteria. The flagellar motor can convert the motive force of protons and other ions to molecular motor rotations. We report on the multi-ion transfer mechanism of the flagellar motor stator MotA/B in Escherichia coli, which primarily utilizes protons. We have identified a leucine amino acid residue as the gateway for H3O+ diffusion. Mutations of a key valine residue cause a narrowing of the channel that is consistent with the size-dependent ion selectivity. We also show that the protonation/deprotonation cycle induces a ratchet motion in the stator, which can couple to the motor rotation. Ion selectivity and the ratchet motion are key to understanding the mechanism of the flagellar motor.