Stall force of polymerizing microtubules and filament bundles

TL;DR

This paper derives an exact expression for the stall force of polymerizing microtubules and filament bundles, revealing its dependence on filament number and lateral interactions, with implications for understanding cellular mechanics.

Contribution

It introduces the concept of polymerization cycles to analytically determine the stall force, showing its independence from ensemble geometry and load distribution.

Findings

Stall force is proportional to the number of filaments.

Stall force increases linearly with lateral filament interaction strength.

Ensemble geometry significantly affects growth kinetics below stall force.

Abstract

We investigate stall force and polymerization kinetics of rigid protofilaments in a microtubule or interacting filaments in bundles under an external load force in the framework of a discrete growth model. We introduce the concecpt of polymerization cycles to describe the stochastic growth kinetics, which allows us to derive an exact expression for the stall force. We find that the stall force is independent of ensemble geometry and load distribution. Furthermore, the stall force is proportional to the number of filaments and increases linearly with the strength of lateral filament interactions. These results are corroborated by simulations, which also show a strong influence of ensemble geometry on growth kinetics below the stall force.