title: Mechanism and kinetics of a sodium-driven bacterial flagellar motor.
abstract: The bacterial flagellar motor is a large rotary molecular machine that propels swimming bacteria, powered by a transmembrane electrochemical potential difference. It consists of an ∼50-nm rotor and up to ∼10 independent stators anchored to the cell wall. We measured torque-speed relationships of single-stator motors under 25 different combinations of electrical and chemical potential. All 25 torque-speed curves had the same concave-down shape as fully energized wild-type motors, and each stator passes at least 37 ± 2 ions per revolution. We used the results to explore the 25-dimensional parameter space of generalized kinetic models for the motor mechanism, finding 830 parameter sets consistent with the data. Analysis of these sets showed that the motor mechanism has a "powerstroke" in either ion binding or transit; ion transit is channel-like rather than carrier-like; and the rate-limiting step in the motor cycle is ion binding at low concentration, ion transit, or release at high concentration.
authors.affiliation: Department of Physics and Graduate Institute of Biophysics, National Central University, Jhongli, Taiwan 32001, Republic of China.
authors.forename: Chien-Jung
authors.initials: CJ
authors.lastname: Lo
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Sowa
authors.forename: Teuta
authors.initials: T
authors.lastname: Pilizota
authors.forename: Richard M
authors.initials: RM
authors.lastname: Berry
mesh_terms: D018407:Bacterial Physiological Phenomena; D005407:Flagella / Q000502:physiology*; D007700:Kinetics; D012964:Sodium / Q000502:physiology*
chemical_list: D012964:Sodium
keywords: ion-motive force; molecular motor; multidimensional modeling; single-molecule; sodium-motive force