Mechanism and kinetics of a sodium-driven bacterial flagellar motor

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

Research output: Contribution to journalArticlepeer-review

43 Scopus citations


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 ∼50-nm rotor and up 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-E25511
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number28
StatePublished - 9 Jul 2013


  • Ion-motive force
  • Molecular motor
  • Multidimensional modeling
  • Single-molecule
  • Sodium-motive force


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