The force exerted by a single kinesin molecule against a viscous load

Area of Science:

• Biophysics
• Molecular Motor Mechanics
• Cellular Transport

Background:

• Kinesin is a crucial motor protein responsible for intracellular transport along microtubules.
• It utilizes adenosine triphosphate (ATP) hydrolysis to generate mechanical force.
• Understanding the chemical-to-mechanical energy transduction mechanism is vital for cell biology.

Purpose of the Study:

• To investigate the force generation mechanism of kinesin.
• To probe the relationship between motor protein function and external load.
• To differentiate between proposed models of kinesin's energy transduction.

Main Methods:

• Utilized a low-density motility assay with kinesin-coated glass surfaces.
• Perturbed microtubule movement by increasing buffer viscosity ~100-fold using polysaccharides and polypeptides.
• Measured microtubule speed under varying drag forces to determine force output.

Main Results:

• Microtubule speed showed a linear dependence on the drag force exerted by the fluid.
• Longer microtubules experienced greater drag and moved slower than shorter ones.
• Extrapolation indicated a maximum time-averaged drag force of 4.2 ± 0.5 pN per single kinesin motor.

Conclusions:

• The observed force output contradicts simple "ratchet" models relying on diffusion at high viscosity.
• Data are consistent with models where kinesin force arises from strain within an elastic element.
• Findings support Huxley-type ratchet or "power-stroke" models for kinesin's mechanical action.