Sol-gel transition in the actin cytoskeleton*

The actin cytoskeleton contains numerous actin binding proteins that are able to regulate its dynamic behavior. This dynamic behavior is mainly controlled by actin treadmilling and motor walking, but it can also be influenced by other proteins such as cross-linker and branchers. In this work we use ordinary differential equations and stochastic mechanochemical simulations to model how three different actin binding proteins: non-muscle myosin IIA (NMIIA), α-actinin, and Arp2/3 bind to actin filaments. Then we analyze how the connectivity, as described by the Flory-Stockmayer theory, changes as a function of the concentration of the actin binding proteins on both models. We find that the sol-gel transition in the system occurs at lower concentrations of linker and motors than those required to observe contractions in the mechanochemical simulations. Finally we compare this result with actin networks containing Arp2/3. We expect our results to give an insight into how the connectivity of the network affects its dynamic behavior.