Single kinesin molecules stressed with optical tweezers

Area of Science:

• Molecular motor proteins
• Biophysics
• Cellular mechanics

Background:

• Kinesin is a molecular motor that transports cargo along microtubules.
• Understanding kinesin's mechanical properties is crucial for cell motility and intracellular transport.
• Previous studies have explored kinesin's force generation but less is known about its response to torsional stress.

Purpose of the Study:

• To investigate the mechanical properties of single kinesin molecules under both stretching and torsional stress.
• To determine if kinesin attachment sites slip under different mechanical loads.
• To elucidate the mechanisms of mechanochemical transduction in kinesin.

Main Methods:

• Utilized optical tweezers to apply controlled forces and torques to single kinesin molecules adsorbed to glass surfaces.
• Stretched and twisted kinesin-bound microtubules to measure responses.
• Analyzed data for apparent stretch, force, torque, and rotational slippage.

Main Results:

• The mechanical system demonstrated high compliance, with significant stretch (< 120 nm) under low force (< 2 pN).
• Kinesin attachment sites did not slip during stretching.
• Under torsional stress (< 2 pN-microns), kinesin showed significant slippage, with microtubules rotating freely around the attachment site.
• Rare instances of torsional elasticity were observed, but restoring forces were inconsistent, further indicating slippage.

Conclusions:

• Kinesin exhibits distinct behaviors under linear and torsional stress, with a propensity for slippage under torque.
• Mechanisms of kinesin's force generation must reconcile linear force production with observed angular slippage.
• These findings provide new insights into the complex mechanics of molecular motors and their interaction with microtubules.