Stress Generation by Actin-Myosin Networks and Bundles

Forces and stresses generated by the action of myosin minifilaments are calculated in idealized computer-generated actin networks and bundles. The networks are generated as random collections of actin filaments in two dimensions, and bundles are obtained by constraining the filament orientations. The actin filaments are crosslinked and attached to two fixed walls. Myosin minifilaments are placed on actin filament pairs and allowed to move and deform the network so that it exerts forces on the walls. The vast majority of simulation runs end with contractile minifilament stress, because minifilaments rotate into energetically stable contractile configurations. This process is aided by the bending of actin filaments, which accomodates minifilament rotation. Stresses for bundles are greater than those for isotropic networks, and antiparallel filaments generate more tension than parallel filaments. The forces transmitted by the actin network to the walls of the simulation cell often exceed the tension in the minifilament itself.