The role of multivalent actin-binding proteins in remodeling actomyosin networks*

We explore the contribution of multivalent actin-binding proteins (ABPs) in remodeling actomyosin networks by using mesoscopic computer simulations. We model ABPs as junctions with varied multi-valencies that enable bundling or branching of actin filaments, which result in diverse morphologies of actomyosin networks. We developed network theory-based order parameters that quantify connectivity between graph nodes in order to analyze emergent morphologies in actomyosin networks. First, we show that ABPs, such as calmodulin-dependent kinase II (CaMKII), with multivalency greater than two not only increase the thickness of actin bundles, but also promote their arborization. Second, myosin motor proteins accelerate the arborization of actin filaments bundled by CaMKII. Because CaMKII is as abundant as actin filaments in neurons, it plays an important role in remodeling the morphology of actin filaments in actomyosin networks; CaMKII’s chemical binding to actin filaments alters the mechanical properties of actomyosin networks that underpin the plasticity of dendritic spines.