Supplementary Figure 8: Schematic illustration depicting polymerization of individual actin filaments nucleated by formins.
From: Cellular chirality arising from the self-organization of the actin cytoskeleton
(a) Polarized actin filaments (green) capped by a formin dimer (blue-red). The first three actin subunits in the two actin helices are numbered 1–3 and 1’-3’ respectively. The formin dimer is immobilized while the opposite end of the actin filament is not. Unconstrained actin filaments rotate in the positive angular direction about x-axis (magenta arrow), as experimentally shown by Mizuno et al.50. (b) Actin filaments are prevented from rotating via immobilization of barbed end by formin and trapping of opposite end by α-actinin cross-linking. Immobile actin subunits are labeled in yellow. Torsional elastic energy accumulated during polymerization is periodically released via high amplitude rotation (“screw-step” highlighted by gray background) in the negative direction (yellow arrow). See details in Shemesh et al.49. See also Supplementary Videos 17 and 18).
