Coarse-grained simulations elucidate mechanical sorting principles in the actin cytoskeleton

In cells, actin binding proteins (ABPs) segregate to different cytoskeletal networks to perform distinct functions, such as forming filopodaie to enable cell migration, or polarizing actin bundles to enable cell division. Recent experimental work has found that mechanical principles may drive this segregation. For example, the binding of a short crosslinker protein to two actin filaments may promote the binding of other short crosslinkers, and inhibit the binding of longer crosslinkers due to the actin’s bending rigidity. We use coarse grained simulation to measure the magnitude of sorting as a function of the mechanical characteristics of actin and ABPs, and predict the energetic competition associated with this sorting mechanism. We also use simulation to determine actin network characteristics that yield material separation through emergent surface tension, such as in actin liquid crystals. Our work can therefore be used to engineer self-sorting biomimetic materials and understand how the heterogeneous distribution of molecules in cells drives biological processes.