Processivity of Myosin Minifilaments: ATP Dependence and Effect on Network Dynamics

Motors proteins like myosin and kinesin are a major source of activity in cellular mechanisms like cell division and perform tasks such as maintaining cellular structure and transporting cargo within the cell. Myosin motors form medium sized (~100 motors) assemblies called myosin minifilaments that bind to and generate forces among actin filaments. The mechano-chemical cycle of individual motors in the motor assembly is dependent on ATP. We are exploring the concentration of ATP as a control parameter for the processivity (walking distance) of myosin minifilaments through stochastic modelling. Here we propose processivity as a parameter to tune the activity in actomyosin system. On the cellular scale, we explore the effect of processivity on cytoskeletal network structures at large. We show that a decrease in ATP concentration increases the processivity of myosin assemblies. However, the velocity of motor assembly also decreases with decreasing ATP. Thus, an optimal trade-off between processivity and velocity must be maintained for efficient assembly performance. To study the effect of processivity on network level structures, we use the simulation package Cytosim. The simulation shows that higher processivity leads to a more pronounced contraction of the actin network.