Mechanism and kinetics of a sodium-driven bacterial flagellar motor

Chien-Jung Lo, Yoshiyuki Sowa, Teuta Pilizota, Richard M. Berry*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The bacterial flagellar motor is a large rotary molecular machine that propels swimming bacteria, powered by a transmembrane electrochemical potential difference. It consists of an similar to 50-nm rotor and up to similar to 10 independent stators anchored to the cell wall. We measured torque-speed relationships of single-stator motors under 25 different combinations of electrical and chemical potential. All 25 torque-speed curves had the same concave-down shape as fully energized wild-type motors, and each stator passes at least 37 +/- 2 ions per revolution. We used the results to explore the 25-dimensional parameter space of generalized kinetic models for the motor mechanism, finding 830 parameter sets consistent with the data. Analysis of these sets showed that the motor mechanism has a "powerstroke" in either ion binding or transit; ion transit is channel-like rather than carrier-like; and the rate-limiting step in the motor cycle is ion binding at low concentration, ion transit, or release at high concentration.

Original languageEnglish
Pages (from-to)E2544-E2551
Number of pages8
JournalProceedings of the National Academy of Sciences
Issue number28
Publication statusPublished - 9 Jul 2013


  • ion-motive force
  • multidimensional modeling
  • sodium-motive force
  • molecular motor
  • single-molecule
  • torque-speed relationship
  • escherichia-coli
  • rotary motor
  • na+-driven
  • zero load
  • proton translocation
  • generating units
  • myosin-v
  • rotation
  • model

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