Molecular friction in an actomyosin molecular machine

Area of Science:

• Muscle physiology
• Biophysics
• Molecular motor function

Background:

• Muscle contraction involves a binding state between actin and myosin in the presence of Mg-ATP.
• Estimating the magnitude of this actin-myosin binding strength is crucial for understanding muscle mechanics.

Purpose of the Study:

• To introduce a novel concept of frictional phenomena to estimate actin-myosin binding strength.
• To validate the proposed theory using experimental movement assay systems.

Main Methods:

• Applied a friction model relating sliding speed to bond strength.
• Utilized two in vitro movement assays without external load: F-actin on myosin-coated surfaces and myosin-coated beads on actin cables.
• Incorporated kinetic friction coefficients, sliding force per cross-bridge, and sliding speed into calculations.

Main Results:

• The study found that the sliding speed is a function of the actin-myosin bond strength.
• Using a kinetic friction coefficient of 0.005, a sliding force of 1 pN per cross-bridge, and a sliding speed of 10 microns/sec, the actin-myosin bond strength was calculated.
• The estimated bond strength between actin and a single myosin head is approximately 200 pN in the contracting state.

Conclusions:

• The frictional phenomena concept provides a method to estimate actin-myosin binding strength.
• The findings offer quantitative insights into the forces involved in muscle contraction at the molecular level.