Collective behaviors of actin filaments in the motility assay with mobile myosin motors

Cells require mechanical forces for their biological functions. The mechanical forces are generated mainly from molecular interactions between actin filaments and myosin motors in the actin cytoskeleton. To better understand their molecular interactions, many studies employed myosin motility assays with actin filaments propelled by myosin heads fixed on a surface. Although these previous studies have shown a wide variety of collective behaviors of actin filaments, the assumption of spatially fixed myosin motors is less physiologically relevant. We employed our computational model for the motility assay with consideration of motor mobility. In agreement with recent experimental results obtained with myosin motors coupled to a lipid bilayer, our simulations showed that actin filaments form large aggregates as opposed to thin bundles as motor mobility increases. Furthermore, this aggregate formation is characterized by the polarity sorting of filaments. Analysis of our simulations shows that polarity sorting and aggregate formation can be explained by a change in collusion statistics between filaments and a phase separation between filaments and motors.