Evidence for symmetry in the elementary process of bidirectional torque generation by the bacterial flagellar motor
Shuichi Nakamura a, Nobunori Kami-ike a, Jun-ichi P. Yokota a, Tohru Minamino a,b, and Keiichi Namba a,1
-Author Affiliations
aGraduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan; and
bPrecursory Research for Embryonic Science and Technology; Japan Science and Technology Agency (PRESTO, JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
Edited by Charles S. Peskin, New York University, and approved August 3, 2010 (received for review May 27, 2010)
Abstract
The bacterial flagellar motor can rotate in both counterclockwise (CCW) and clockwise (CW) directions. It has been shown that the sodium ion-driven chimeric flagellar motor rotates with 26 steps per revolution, which corresponds to the number of FliG subunits that form part of the rotor ring, but the size of the backward step is smaller than the forward one. Here we report that the proton-driven flagellar motor of Salmonella also rotates with 26 steps per revolution but symmetrical in both CCW and CW directions with occasional smaller backward steps in both directions. Occasional shift in the stepping positions is also observed, suggesting the frequent exchange of stators in one of the 11–12 possible anchoring positions around the rotor. These observations indicate that the elementary process of torque generation by the cyclic association/dissociation of the stator with every FliG subunit along the circumference of the rotor is symmetric in CCW and CW rotation even though the structure of FliG is highly asymmetric and suggests a 180° rotation of a FliG domain for the rotor-stator interaction to reverse the direction of rotation.
FliG, MotAB stator complex, Salmonella, stepping rotation, switch
Footnotes
1To whom correspondence should be addressed.
E-mail: keiichi@fbs.osaka-u.ac.jp.
Author contributions: S.N., T.M., and K.N. designed research; S.N., N.K., J.-i.P.Y., and T.M. performed research; S.N. and N.K. analyzed data; and S.N., T.M., and K.N. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
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