Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 108, Issue 41, Pages 17171-17176Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1110111108
Keywords
molecular machines; motility; signal transduction
Categories
Funding
- National Institutes of Health [R01GM64664]
- Dale A. Stringfellow Graduate Fellowship in Cellular and Molecular Biology
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The direction of flagellar rotation is regulated by a rotor-mounted protein assembly, termed the switch complex, formed from multiple copies of the proteins FliG, FliM, and FliN. The structures of major parts of these proteins are known, and the overall organization of proteins in the complex has been elucidated previously using a combination of protein-binding, mutational, and cross-linking approaches. In Escherichia coli, the switch from counter-clockwise to clockwise rotation is triggered by the signaling protein phospho-CheY, which binds to the lower part of the switch complex and induces small movements of FliM and FliN subunits relative to each other. Direction switching also must produce movements in the upper part of the complex, particularly in the C-terminal domain of FliG (FliG(C)), which interacts with the stator to generate the torque for flagellar rotation. In the present study, protein movements in the middle and upper parts of the switch complex have been probed by means of targeted cross-linking and mutational analysis. Switching induces a tilting movement of the FliM domains that form the middle part of the switch and a consequent rotation of the affixed FliGC domains that reorients the stator interaction sites by about 90 degrees. In a recently proposed hypothesis for the motor mechanism, such a reorientation of FliGC would reverse the direction of motor rotation.
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