Non-canonical Actomyosin Interactions Couple a Broad Spectrum of F-actin Bending Modes

The cell cortex is a 2-dimensional network made of semi-flexible F-actin polymers driven out-of-equilibrium by molecular motors. Myosin is a molecular motor protein whose canonical interactions include the relative sliding of F-actin, leading to tensile loading and contraction of the polymer network. Here, we report non-canonical actomyosin interactions in in vitro quasi-2D, stable and non-contractile actomyosin networks that result in non-equilibrium fluctuations of the endogenous polymers. Below the concentration of myosin required to contract, myosin motors induce large and anomalous deformations of F-actin polymers transverse to the F-actin long axis. These enhanced fluctuations are found to break detailed balance, indicating that myosin activity couples F-actin bending modes across a broad spectrum. These correlations cannot arise from an increased effective temperature, and the resulting active stresses are dissipated across all length scales in stable actomyosin networks. Filament curvature is thus implicated in network stability while it has previously only been associated with contractility.