A hidden state in the turnover of a functioning membrane protein complex

Area of Science:

• Molecular and Cellular Biology
• Biophysics
• Microbiology

Background:

• Membrane proteins function in dynamic complexes crucial for cellular processes.
• The bacterial flagellar motor is a rotary motor essential for bacterial motility.
• Stator units drive flagellar motor rotation, and their turnover between the motor and membrane pool is known.

Purpose of the Study:

• To elucidate the unclear kinetics of stator turnover in the bacterial flagellar motor.
• To investigate the dynamics of torque-generating units in individual motors.

Main Methods:

• Direct measurement of stator turnover kinetics using long-term, high-resolution recordings of bacterial flagellar motor speed.
• Analysis of motor speed data under high load conditions.
• Statistical analysis of stator dwell time distributions.

Main Results:

• Stator dwell time distributions exhibit a multi-exponential shape.
• This complex distribution suggests a previously uncharacterized hidden state in stator turnover.
• Kinetics of stator unit exchange were directly measured at the single-motor level.

Conclusions:

• The bacterial flagellar motor stator turnover is more complex than previously understood.
• A hidden state likely plays a role in the dynamics of stator unit exchange.
• These findings advance our understanding of molecular motor function and regulation.