Tension and chemical efficiency of Myosin-II motors

TL;DR

This paper revises the Brownian ratchet model to analyze Myosin-II motors, revealing how electrostatic effects influence tension, mechanosensing, and chemical efficiency, which varies with the number of motor heads.

Contribution

It introduces a modified Brownian ratchet model incorporating electrostatic effects and defines a new chemical efficiency measure related to active tension in Myosin-II motors.

Findings

Chemical efficiency varies with the number of motor heads.

Motors with few heads have maximal efficiency when frustrated.

The model demonstrates mechanosensing capabilities of Myosin-II motors.

Abstract

Recent experiments demonstrate that molecular motors from the Myosin II family serve as cross-links inducing active tension in the cytoskeletal network. Here we revise the Brownian ratchet model, previously studied in the context of active transport along polymer tracks, in setups resembling a motor in a polymer network, also taking into account the effect of electrostatic changes in the motor heads. We explore important mechanical quantities and show that such a model is also capable of mechanosensing. Finally, we introduce a novel efficiency based on excess heat production by the chemical cycle which is directly related to the active tension the motor exerts. The chemical efficiencies differ considerably for motors with a different number of heads, while their mechanical properties remain qualitatively similar. For motors with a small number of heads, the chemical efficiency is maximal when they are frustrated, a trait that is not found in larger motors.