Scale dependence of mechanics and dynamics of active gels with increasing motor concentration

TL;DR

This study investigates how motor protein aggregate size influences the mechanics and dynamics of actin-based active gels, revealing universal stiffness effects and size-dependent active fluctuations with non-Gaussian behavior.

Contribution

It demonstrates that motor aggregate size affects active gel fluctuations and mechanics, with universal stiffness effects and unique fluctuation statistics based on assembly size.

Findings

Motor aggregates increase gel stiffness universally.

Active fluctuations depend on motor assembly size.

Small motor assemblies show non-Gaussian fluctuation statistics.

Abstract

The cytoskeleton protein actin assembles into large bundles when supporting stresses in the cell, but grows into a fine branched network to induce cell motion. Such self-organization processes are studied in artificial networks of cytoskeleton proteins with thick actin bundles and large motor protein aggregates to enable optical observation. The effect of motor aggregate size on the cytoskeleton mechanical properties is studied here in networks comprised of much smaller motor assemblies. Large motor protein clusters are known to increase the stiffness of actin based networks by introducing tension and additional cross-linking cites. We find that these effects are universal to actin gels regardless of actin bundle thickness and motor aggregate size and are relevant, therefore, to a wide range of cytoskeleton based cellular processes. In contrast, motor induced active fluctuations depend significantly on motor assembly size, featuring unique non-Gaussian statistics at high concentrations of small assemblies.