Single kinesin molecules studied with a molecular force clamp.

Area of Science:

• Molecular motor protein function
• Mechanochemistry of kinesin motors
• Cellular transport mechanisms

Background:

• Kinesin is an ATP-driven motor protein that moves along microtubules in 8 nm steps.
• The precise coupling mechanism between ATP hydrolysis and mechanical movement in kinesin is not fully understood.
• Understanding this process is crucial for comprehending intracellular transport.

Purpose of the Study:

• To investigate the mechanochemical details of kinesin motor protein function.
• To elucidate how chemical energy from ATP is converted into mechanical work.
• To analyze kinesin's response to varying ATP concentrations and external loads.

Main Methods:

• Development of a novel force clamp instrument using a feedback-driven optical trap.
• Measurement of single kinesin motor motion under controlled, constant loads.
• Analysis of kinesin's mechanochemical behavior across different ATP concentrations and forces.

Main Results:

• Kinesin stepping is tightly coupled to ATP hydrolysis (one hydrolysis per 8 nm step) across a broad force range.
• The kinesin stall force is dependent on ATP concentration.
• Increased mechanical loads reduce maximum velocity and increase the Michaelis-Menten constant, indicating load-dependent transitions in the kinesin cycle.

Conclusions:

• The kinesin motor cycle involves at least one load-dependent transition affecting ATP binding and hydrolysis commitment.
• Another load-dependent rate likely influences the overall turnover number.
• These findings necessitate a revised understanding of kinesin motor mechanics and function.