Kinesin rotates unidirectionally and generates torque while walking on microtubules

Area of Science:

• Molecular and Cellular Biology
• Biophysics
• Nanotechnology

Background:

• Cytoskeletal motor proteins, like kinesin-1, are crucial for intracellular transport, moving cargo along microtubule tracks.
• Understanding the precise mechanical steps, including rotation, of kinesin-1 is essential for elucidating its function as a cellular machine.
• Previous studies have focused on linear motion, leaving the rotational dynamics of kinesin-1 largely unresolved.

Purpose of the Study:

• To directly measure the simultaneous translocation, rotation, force, and torque produced by individual kinesin-1 motors.
• To investigate the mechanism of kinesin-1's step-wise movement, particularly its rotational component.
• To assess the contribution of rotational work to the overall efficiency of kinesin-1 as a molecular motor.

Main Methods:

• Utilized optical tweezers integrated with an optical microprotractor and torsion balance.
• Employed highly birefringent microspheres to enable simultaneous measurement of linear and rotational motion.
• Measured force and torque generated by single kinesin-1 motors during translocation along microtubules at varying ATP concentrations.

Main Results:

• Kinesin-1 motors did not generate torque at low adenosine 5'-triphosphate (ATP) concentrations.
• At saturating ATP concentrations, motors exhibited unidirectional rotation, generating significant torque.
• The measured torque and rotation, when accounted for, indicate kinesin-1 operates as a highly efficient machine.

Conclusions:

• The findings strongly suggest a rotary hand-over-hand mechanism for kinesin-1's stepping motion.
• Accounting for rotational work reveals kinesin-1's remarkable efficiency as a molecular machine.
• The developed methodology is broadly applicable for studying the mechanics of other molecular motors.