Nonequilibrium simulation of cytoskeletal proteins: assembly, bundling and gelation.*

The cytoskeleton of living cells is a dynamical network with an extremely rich behavior: it maintains the shape of the cell, gives it resistance to deformation, allows it to deform and migrate and provides the structure necessary for intracellular transport. In order to gain a better understanding of the biological role of the cytoskeleton, it is fundamental to understand how it assembles, how it remodels itself and which factors determines its structure.

The competition between filament bundling and elongation is one of the key factors in determining the structure and mechanical properties of the cytoskeleton. In order to capture this out-of-equilibrium process, we simulate a system of "patchy" monomers which can polymerize into long chains through irreversible end-to-end interactions. In addition, the monomers can also stick reversibly to each other via side-by-side interactions. We show that this simple model leads to a very rich range of different behaviors, giving rise to filaments, bundles, and complex bundle/filament networks depending on the thermodynamic parameters considered. We believe our approach to provide valuable insight on the behavior of cytoskeletal networks of bundled proteins, for which a satisfactory theoretical understanding is still lacking.