Force and velocity measured for single kinesin molecules

Area of Science:

• Molecular biology
• Biophysics
• Cellular mechanics

Background:

• Kinesin is a crucial molecular motor protein responsible for intracellular transport.
• Understanding kinesin's mechanical properties under load is vital for elucidating cellular transport mechanisms.

Purpose of the Study:

• To characterize the force-velocity relationship of single kinesin molecules.
• To investigate the coupling mechanism between ATP hydrolysis and mechanical work in kinesin.

Main Methods:

• Utilized optical trapping interferometry for high-precision tracking of kinesin-driven silica beads.
• Measured single-molecule force-velocity curves by applying pN-level forces.
• Analyzed movement at varying ATP concentrations (limiting and saturating).

Main Results:

• Kinesin velocity decreased linearly with increasing applied force.
• Single kinesin molecules sustained loads up to 5-6 pN.
• Load-dependent velocity reduction is attributed to decreased net displacement per ATP, not altered turnover rate.

Conclusions:

• Kinesin functions as a loosely coupled motor protein.
• The motor's efficiency is compromised under load due to reduced step size per ATP hydrolysis.
• Findings provide insights into the mechanical regulation of molecular motors.