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Biophysical Characterization of Flagellar Motor Functions
06:08

Biophysical Characterization of Flagellar Motor Functions

Published on: January 18, 2017

8.7K

MotI (DgrA) acts as a molecular clutch on the flagellar stator protein MotA in Bacillus subtilis

Sundharraman Subramanian1,2, Xiaohui Gao1,2, Charles E Dann3

  • 1Department of Chemistry, Indiana University, Bloomington, IN 47405.

Proceedings of the National Academy of Sciences of the United States of America
|December 3, 2017
PubMed

Insights

MotI acts as a molecular clutch, disengaging bacterial flagellar stators (MotA complexes) to inhibit motility. This mechanism, involving MotI binding to MotA, offers new insights into bacterial flagellar regulation.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Biochemistry

Background:

  • Bacterial flagellar motors are powered by proton flow through stator complexes (MotA4MotB2).
  • These stators interact with the flagellar rotor (FliG) to generate torque for motility.
  • Regulation of flagellar rotation involves mechanisms that disengage or jam stator-rotor interactions.

Purpose of the Study:

  • To investigate the role of the YcgR homolog MotI (formerly DgrA) in regulating bacterial motility in *Bacillus subtilis*.
  • To elucidate the mechanism by which MotI inhibits flagellar rotation.
  • To characterize the structural and functional interactions of MotI with the flagellar stator.

Main Methods:

  • Analysis of flagellar rotation in MotI-inhibited cells and cells with suppressor mutations in MotA.
  • Determination of the 3D crystal structure of MotI bound to cyclic di-GMP (c-di-GMP).
  • Localization studies using MotI-fluorescent fusions in conjunction with MotA.

Main Results:

  • MotI inhibits motility by disengaging the MotA stator from the flagellar rotor, allowing free rotation via Brownian motion.
  • Suppressor mutations in MotA conferring resistance to MotI inhibition were identified near the force-generation site.
  • The crystal structure revealed MotI bound to c-di-GMP, and MotI localized to the membrane in a MotA-dependent manner.

Conclusions:

  • MotI functions as a molecular clutch, reversibly disengaging flagellar stators.
  • This disengagement mechanism involves MotI binding to MotA, sequestering it from the rotor.
  • The findings provide a novel model for flagellar motor regulation through stator-rotor uncoupling.
Keywords:
MotAYcgRc-di-GMPflagellamotility

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