Fig. 4.

Ribbon diagrams showing lateral contacts between subunits along the short-pitch helix. (A) Overview of filament with two subunits highlighted in green and tan. (B) Detail of contacts between subunits a (green) and a-1 (tan) with labels on stick figures of the interacting residues. (C) Same as B with two overlaid actin monomers (light blue) aligned with subdomains 3 and 4. This superimposition shows that subunit flattening allows interactions between the backbone and side chain of E195 in subdomain 4 of subunit a and K113 in subdomain 1 of subunit a-1 and between side chain of E270 in subdomain 3 of subunit a-1 with side chain of R39 in subdomain 2 of subunit a. The red ovals highlight differences.