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Torque-generating units of the flagellar motor of Escherichia coli have a high duty ratio

Nature volume 403, pages 444–447 (2000)Cite this article

Abstract

Rotation of the bacterial flagellar motor is driven by an ensemble of torque-generating units containing the proteins MotA and MotB1,2,3. 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 ratio4. 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 µm s-1, 12 kHz and 1.5 × 105 pN nm s-1, respectively.

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Figure 1: Measurements made at high and low load.
Figure 2: Speeds, measured and simulated.
Figure 3: Torques, measured and simulated.

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Acknowledgements

We thank K. Fahrner and A. Samuel for plasmid and strain constructions, and K. Fahrner, A. Samuel and L. Turner for comments on the manuscript. This work was supported by the Wellcome Trust, the Rowland Institute for Science and by the US NIH.

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Authors and Affiliations

  1. Department of Molecular and Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, 02138, Massachusetts, USA

    William S. Ryu & Howard C. Berg

  2. Rowland Institute for Science, 100 Edwin H. Land Boulevard, Cambridge, 02142, Massachusetts, USA

    William S. Ryu & Howard C. Berg

  3. The Randall Centre, King's College London, London, SE1 1UL, UK

    Richard M. Berry

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Ryu, W., Berry, R. & Berg, H. Torque-generating units of the flagellar motor of Escherichia coli have a high duty ratio. Nature 403, 444–447 (2000). https://doi.org/10.1038/35000233

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