title: Direct observation of steps in rotation of the bacterial flagellar motor.
abstract: The bacterial flagellar motor is a rotary molecular machine that rotates the helical filaments that propel many species of swimming bacteria. The rotor is a set of rings up to 45 nm in diameter in the cytoplasmic membrane; the stator contains about ten torque-generating units anchored to the cell wall at the perimeter of the rotor. The free-energy source for the motor is an inward-directed electrochemical gradient of ions across the cytoplasmic membrane, the protonmotive force or sodium-motive force for H+-driven and Na+-driven motors, respectively. Here we demonstrate a stepping motion of a Na+-driven chimaeric flagellar motor in Escherichia coli at low sodium-motive force and with controlled expression of a small number of torque-generating units. We observe 26 steps per revolution, which is consistent with the periodicity of the ring of FliG protein, the proposed site of torque generation on the rotor. Backwards steps despite the absence of the flagellar switching protein CheY indicate a small change in free energy per step, similar to that of a single ion transit.
authors.affiliation: Department of Applied Physics, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603, Japan.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Sowa
authors.forename: Alexander D
authors.initials: AD
authors.lastname: Rowe
authors.forename: Mark C
authors.initials: MC
authors.lastname: Leake
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Yakushi
authors.forename: Michio
authors.initials: M
authors.lastname: Homma
authors.forename: Akihiko
authors.initials: A
authors.lastname: Ishijima
authors.forename: Richard M
authors.initials: RM
authors.lastname: Berry
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005407:Flagella / Q000502:physiology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D000072236:Methyl-Accepting Chemotaxis Proteins; D020409:Molecular Motor Proteins / Q000235:genetics / Q000378:metabolism*; D018892:Proton-Motive Force; D012399:Rotation; D012964:Sodium / Q000378:metabolism; D013816:Thermodynamics; D019415:Torque; D044149:Vibrio alginolyticus / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C075660:Flig protein, Bacteria; D008565:Membrane Proteins; D000072236:Methyl-Accepting Chemotaxis Proteins; D020409:Molecular Motor Proteins; C000607606:cheY protein, E coli; D000255:Adenosine Triphosphate; D012964:Sodium