Biophys J, February 2000, p. 626-651, Vol. 78, No. 2

An Electrostatic Mechanism Closely Reproducing Observed Behavior in the Bacterial Flagellar Motor

Dieter Walz^* and S. Roy Caplan

 ^*Biozentrum, University of Basel, CH-4056 Basel, Switzerland, and  Department of Biological Chemistry, The Weizmann Institute of Science, 76100 Rehovot, Israel, and Department of Physiology, McGill University, Montreal, Québec H3G 1Y6, Canada

A mechanism coupling the transmembrane flow of protons to the rotation of the bacterial flagellum is studied. The coupling is accomplished by means of an array of tilted rows of positive and negative charges around the circumference of the rotor, which interacts with a linear array of proton binding sites in channels. We present a rigorous treatment of the electrostatic interactions using minimal assumptions. Interactions with the transition states are included, as well as proton-proton interactions in and between channels. In assigning values to the parameters of the model, experimentally determined structural characteristics of the motor have been used. According to the model, switching and pausing occur as a consequence of modest conformational changes in the rotor. In contrast to similar approaches developed earlier, this model closely reproduces a large number of experimental findings from different laboratories, including the nonlinear behavior of the torque-frequency relation in Escherichia coli, the stoichiometry of the system in Streptococcus, and the pH-dependence of swimming speed in Bacillus subtilis.

Biophys J, February 2000, p. 626-651, Vol. 78, No. 2
© 2000 by the Biophysical Society   0006-3495/00/02/626/26  $2.00

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