Broken Detailed Balance of Filament Dynamics in Active Networks

TL;DR

This paper analytically investigates how motor-driven activity in biopolymer networks causes non-equilibrium fluctuations and mode coupling in semiflexible filaments, violating detailed balance and aligning with recent experimental observations.

Contribution

It provides a theoretical framework for understanding non-equilibrium shape fluctuations and mode coupling in semiflexible filaments driven by motor activity.

Findings

Mode coupling leads to non-zero circulatory currents in conformational space.

Predicted characteristic frequencies relate to motor activity signatures.

Results are consistent with recent microtubule fluctuation experiments.

Abstract

Myosin motor proteins drive vigorous steady-state fluctuations in the actin cytoskeleton of cells. Endogenous embedded semiflexible filaments such as microtubules, or added filaments such as single-walled carbon nanotubes are used as novel tools to non-invasively track equilibrium and non-equilibrium fluctuations in such biopolymer networks. Here we analytically calculate shape fluctuations of semiflexible probe filaments in a viscoelastic environment, driven out of equilibrium by motor activity. Transverse bending fluctuations of the probe filaments can be decomposed into dynamic normal modes. We find that these modes no longer evolve independently under non-equilibrium driving. This effective mode coupling results in non-zero circulatory currents in a conformational phase space, reflecting a violation of detailed balance. We present predictions for the characteristic frequencies associated with these currents and investigate how the temporal signatures of motor activity determine mode correlations, which we find to be consistent with recent experiments on microtubules embedded in cytoskeletal networks.