(305i) A Strong Nonequilibrium Bound for Sorting of Cross-Linkers on Growing Biopolymers

Understanding the role of nonequilibrium driving in self-organization is crucial for developing a predictive description of biological systems, yet it is impeded by their complexity. The actin cytoskeleton serves as a paradigm for how equilibrium and nonequilibrium forces combine to give rise to self-organization. Recent experiments show that actin filament growth rates can tune the morphology of a growing actin bundle cross-linked by two competing types of actin-binding proteins [S. L. Freedman et al., Proc. Natl. Acad. Sci. U.S.A. 116, 16192–16197 (2019)]. However, the connection between microscopic driving forces in this system and their emergent structures remains elusive. We tackle this problem by deriving a fluctuation–response bound in the context of actin polymerization and bundling and verify its robustness far from equilibrium through simulation. The thermodynamic constraints reveal the importance of correlations between these molecular fluxes and offer a route to estimating microscopic driving forces from microscopy experiments.