The Force Exerted by a Molecular Motor

TL;DR

This paper presents a general theoretical framework for understanding the stochastic forces generated by molecular motors, applicable to various models and experimentally testable, revealing complex velocity-load behaviors and challenging previous bounds on force estimates.

Contribution

It introduces a universal barometric relation for molecular motor forces that applies across different kinetic models and aligns with Einstein relations near equilibrium.

Findings

Velocity-load plots show diverse shapes, including nonmonotonic behavior.

Previous bounds on driving force are generally invalid.

The framework is consistent with experimental and theoretical models.

Abstract

The stochastic driving force exerted by a single molecular motor (e.g., a kinesin, or myosin) moving on a periodic molecular track (microtubule, actin filament, etc.) is discussed from a general viewpoint open to experimental test. An elementary "barometric" relation for the driving force is introduced that (i) applies to a range of kinetic and stochastic models, (ii) is consistent with more elaborate expressions entailing explicit representations of externally applied loads and, (iii) sufficiently close to thermal equilibrium, satisfies an Einstein-type relation in terms of the velocity and diffusion coefficient of the (load-free) motor. Even in the simplest two-state models, the velocity-vs.-load plots exhibit a variety of contrasting shapes (including nonmonotonic behavior). Previously suggested bounds on the driving force are shown to be inapplicable in general by analyzing discrete jump models with waiting time distributions.