Rare convulsive movements observed in simulations of motorized actin networks with the Arp2/3 complex*

Actomyosin networks are systems of actin filaments that are actively reorganized by motor proteins. Actomyosin networks are essential for providing structural scaffolds to cells and are involved in cell movement, growth, and division. The dynamics of these networks are regulated by many actin-binding proteins. In this work, we simulate the reorganizations of motorized actin networks with and without the actin-related protein 2/3 (Arp2/3) complex. We include motor proteins (non-muscle myosin IIA heavy chain (NMIIA)) and cross-linking proteins (α-actinin) in both actin systems. We observe that the relaxation times of the branched actomyosin networks are significantly longer than those of their unbranched counterparts, by as much as a factor of 4. We also observe that the branched networks exhibit rare convulsive movements, which we call avalanches. These avalanches release tension in the network. Recent experimental evidence of “cytoquakes” are consistent with the results of our simulations.