Unfolding cross-linkers as rheology regulators in F-actin networks

TL;DR

This paper investigates how cross-linkers with unfolding domains, like Filamin, influence the nonlinear rheological behavior of F-actin networks, revealing a strain-induced softening and self-organization at the molecular level.

Contribution

It introduces a mean-field model explaining the network's organization at the unfolding threshold and links it to observed power-law relaxation phenomena.

Findings

Unfolding domains cause shear softening beyond a strain threshold.

Network self-organizes with many cross-linkers at the unfolding threshold.

Model explains power-law relaxation in microrheology experiments.

Abstract

We report on the nonlinear mechanical properties of a statistically homogeneous, isotropic semiflexible network cross-linked by polymers containing numerous small unfolding domains, such as the ubiquitous F-actin cross-linker Filamin. We show that the inclusion of such proteins has a dramatic effect on the large strain behavior of the network. Beyond a strain threshold, which depends on network density, the unfolding of protein domains leads to bulk shear softening. Past this critical strain, the network spontaneously organizes itself so that an appreciable fraction of the Filamin cross-linkers are at the threshold of domain unfolding. We discuss via a simple mean-field model the cause of this network organization and suggest that it may be the source of power-law relaxation observed in in vitro and in intracellular microrheology experiments. We present data which fully justifies our model for a simplified network architecture.