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Non-equilibrium effect in the allosteric regulation of the bacterial flagellar switch

Nature Physics volume 13, pages 710–714 (2017)Cite this article

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Abstract

The switching mechanism of the flagellar motor provides the basis for the motile behaviour of flagellated bacteria. Its highly sensitive response has previously been understood in terms of equilibrium models, either the classical two-state concerted allosteric model, or more generally, the Ising-type conformation spread model. Here, we systematically study motor switching under various load conditions from high to zero load, under different proton motive force (pmf) conditions and varying the number of torque-generating units (stators). In doing so, we reveal the signature of a non-equilibrium effect. To consistently account for the motor-switching dependence on each those conditions, a previously neglected non-equilibrium effect—the energy input from the motor torque—has to be incorporated into models of the flagellar switch. We further show that this effect increases the sensitivity of the flagellar switch. Exploiting a very small fraction of the energy expense of the flagellar motor for functional regulation increases its sensitivity greatly. Similar mechanisms are expected to be found in other protein complexes.

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Figure 1: CCW (top) and CW (bottom) interval distributions for 149 motors of cells expressing cheY13DK106YW with 0.5-μm-diameter latex beads attached to short filament stubs.
Figure 2: CCW interval distributions for motors with different number of stators measured in motor resurrection experiments for motors in the CW bias group of 0.5 ± 0.1.
Figure 3: Modelling the flagellar switch.
Figure 4: Motor dose–response curve (CW bias versus CheY-P level) at zero load and high load simulated using the non-equilibrium conformation spread model.

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Acknowledgements

We thank H. Berg, J. Tang, and Y. Tu for comments. This work was supported by National Natural Science Foundation of China Grants 11374282, 21573214 (to J.Y.) and 11402265 (to R.Z.), Fundamental Research Funds for the Central Universities (WK2030020023, to J.Y.), and Anhui Natural Science Foundation Grant 1408085MA10 (to R.Z.). J.Y. and R.Z. are supported by the Chinese Government ‘1000 Youth Talent Program’.

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  1. Fangbin Wang, Hui Shi and Rui He: These authors contributed equally to this work.

Authors and Affiliations

  1. Hefei National Laboratory for Physical Sciences at the Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China

    Fangbin Wang, Hui Shi, Rui He, Renjie Wang, Rongjing Zhang & Junhua Yuan

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  1. Fangbin Wang
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Contributions

J.Y. and R.Z. planned the work; F.W., H.S. and R.H. performed the measurements and the simulation with help from R.W.; J.Y. proposed the non-equilibrium model; J.Y., R.Z. and F.W. wrote the paper with inputs from other authors.

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Correspondence to Rongjing Zhang or Junhua Yuan.

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Wang, F., Shi, H., He, R. et al. Non-equilibrium effect in the allosteric regulation of the bacterial flagellar switch. Nature Phys 13, 710–714 (2017). https://doi.org/10.1038/nphys4081

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