Computational Analysis of a Cross-linked Actin-like Network

Gels formed from G-actin or other filament-forming monomers exhibit a range of morphologies that differ widely in terms of pore size, fiber diameter, degree of isotropy, and frequency of cross-linking or branching. These characteristics are determined, in large part, by the nature and concentration of the proteins that form cross-links between single filaments, yet little is known how filament-forming monomers and cross-linkers assemble to generate a particular network morphology. Some of the important attributes of a cross-linker are the spatial and angular orientation of its two filament binding sites, its size, and stiffness to both rotation and extension. Here, we introduce a Brownian dynamics (BD) simulation model in three dimensions in which actin monomers polymerize and become cross-linked by two types of cross-linking molecules that form either parallel filament bundles or perpendicular cross-links. We analyze the effects of various system parameters on the growth and morphology of the resulting network. Some scaling behaviors emerge that are insensitive to the detailed choice of parameters. Our model thus has the potential as a base BD model that can be further refined for investigating various actin-related phenomena.