Fig. 4

Actin–cofilin interactions. In a–e and g–i, the P-end is at the top. a–f Actin and cofilin are presented in camel and orange, respectively. The F-site (Cofilin-B-subunit interface), Go site (Cofilin-SD1 of the P-subunit interface), Gi_l site (Cofilin-ID of the P-subunit interface with long-range interactions) and Gi_s-sites (Cofilin-ID of the P-subunit interface which is not included in the Gi_l site) in the actin subunits are shown in blue, red, brown and yellow, respectively. In cofilin, residues forming the F-sites and G-sites are represented in blue and green, respectively. a Two actin subunits and the bound cofilin are presented. b Cofilin was removed from a. c Cofilin in a is rotated by 180°. d Residues contributing to the Gi_l-site are shown as a space-filling model. e A 50° rotation of d. f Residues within the Gi_s-sites and Go-sites are presented as sticks in an end-on view of the 111–119 helix of cofilin. g–i Models showing the steric hindrance expected when cofilin binds to F-actin. Colliding atoms on both actin and cofilin are represented as a space-filling model in blue and red, respectively. The other atoms of the residues containing the colliding atoms are represented as a stick model. g A model of cofilin bound to the actin filament through the F-site. No collisions occur. h A model of cofilin bound through the Gi-site. i A model of cofilin bound through the Go-site