Critical state enhances cross-linker denaturation under stress in biopolymer networks

We report on the statistical behavior of cross-linker molecules containing numerous unfolding domains when they are used to bind a random semiflexible polymer network. Cross-linkers with unfolding domains are ubiquitous in the F-actin component of the cytoskeleton - examples include filamin and a-actinin. We show, through mean field calculations and simulations, that under tension the cross-linkers naturally organize into a critical state which greatly enhances their propensity to unfold. Unfolding of cross-links could play a role in stress-regulation and mechanotransduction. The critical state is characterized by an exponential or faster growth in the population of cross-linkers as a function of tension up to a characteristic unfolding tension. This critical state should occur at physiologically relevant stress levels in any open random network built with such cross-linkers.