title: Torque-generating units of the flagellar motor of Escherichia coli have a high duty ratio.
abstract: Rotation of the bacterial flagellar motor is driven by an ensemble of torque-generating units containing the proteins MotA and MotB. Here, by inducing expression of MotA in motA- cells under conditions of low viscous load, we show that the limiting speed of the motor is independent of the number of units: at vanishing load, one unit turns the motor as rapidly as many. This result indicates that each unit may remain attached to the rotor for most of its mechanochemical cycle, that is, that it has a high duty ratio. Thus, torque generators behave more like kinesin, the protein that moves vesicles along microtubules, than myosin, the protein that powers muscle. However, their translation rates, stepping frequencies and power outputs are much higher, being greater than 30 microm s(-1), 12 kHz and 1.5 x 10(5) pN nm s(-1), respectively.
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: W S
authors.initials: WS
authors.lastname: Ryu
authors.forename: R M
authors.initials: RM
authors.lastname: Berry
authors.forename: H C
authors.initials: HC
authors.lastname: Berg
mesh_terms: D001426:Bacterial Proteins / Q000502:physiology; D004926:Escherichia coli / Q000502:physiology*; D005407:Flagella / Q000502:physiology*; D008565:Membrane Proteins / Q000502:physiology; D008954:Models, Biological; D020409:Molecular Motor Proteins / Q000502:physiology*; D019415:Torque
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D020409:Molecular Motor Proteins; C063010:MotA protein, Bacteria