Structural Organization and Energy Storage in Crosslinked Actin-Assemblies

Clathrin-mediated endocytosis (CME) is a key process in membrane trafficking. During CME, a patch of flat membrane is invaginated into an omega-shaped tubule and pinched off into a vesicle. In yeast, this membrane deformation is hindered by high turgor pressure, and actin machineries are required to produce the forces counteracting the turgor pressure. How actin filaments are organized to generate the forces remains unclear due to the small dimension (100nm) of the structure. In this talk, I will present our simulations of self-organization of rigid actin filaments in the presence of elastic crosslinkers. We found that actin filaments condensed into a disordered meshwork or an ordered bundle in free space. Around a cylinder, actin filaments formed a tensed ring-like structure that tends to constrict the cylinder. Our simulations also demonstrated that these nanometer-scale actin structures could store a large amount of elastic energy within the crosslinkers (up to 10kBT per crosslinker). This conversion of binding energy into elastic energy is the consequence of geometric constraints created by the helical pitch of the actin filaments, which results in frustrated configurations of crosslinkers attached to filaments.