Multiple kinetic states for the flagellar motor switch.

Area of Science:

• Microbiology
• Biophysics
• Molecular Biology

Background:

• Escherichia coli flagellar motors are complex molecular machines responsible for bacterial motility.
• Understanding the kinetic states of flagellar motors is crucial for deciphering bacterial chemotaxis.
• Previous models often simplified the motor's dynamic behavior.

Purpose of the Study:

• To investigate the kinetic states of Escherichia coli flagellar motors using high-resolution analysis.
• To characterize the behavioral effect of CheY on single flagellar motors.
• To determine an appropriate kinetic model for flagellar motor function.

Main Methods:

• Computerized video processing system for high-resolution analysis of flagellar motors.
• Utilized wild-type Escherichia coli and a modified strain (RP1091) with altered signal-transducing genes.
• Quantified the ultrasensitive behavioral effect of CheY on motor rotation.

Main Results:

• Identified multiple kinetic states for both clockwise and counterclockwise rotation in flagellar motors.
• Observed new kinetic states in both wild-type and modified strains.
• Demonstrated an ultrasensitive behavioral effect of CheY with a Hill coefficient of 5.5 +/- 1.9.
• Ruled out a two-state model, with data best fitting a four-state model.

Conclusions:

• The kinetic behavior of Escherichia coli flagellar motors is more complex than previously modeled.
• A four-state model, comprising two clockwise and two counterclockwise states, accurately describes the observed motor dynamics.
• CheY exhibits an ultrasensitive, switch-like effect on flagellar motor function.