Fig. 3: Actin–Arp2/3 complex interaction surfaces within the branch junction.

a Interaction surfaces between the Arp2/3 complex, and the actin mother and daughter filament. The surfaces for the Arp2/3 complex, mother and daughter filament are shown as density maps at 9.5 Å resolution generated from their respective models. Gray coloring on the surface of Arp2/3 subunits indicates contact sites with actin and coloring of actin subunits in a specific color indicates a contact site with the associated Arp2/3 subunit. Subunit colors are annotated in the figure with Arp2 being red, Arp3 orange, ArpC1 green, ArpC2 light blue, ArpC3 violet, ArpC4 dark blue, and ArpC5 yellow. Actin is shown in gray. The numbering of the mother (M#) and daughter (D#) filament subunits is also indicated. Coloring was applied via the color zone command in ChimeraX in a 5.5 Å radius around each C-alpha atom of the underlying model, which was positioned in a 10 Å radius to a C-alpha atom of its putative interactor. b Surface representation of the interaction of ArpC2 and ArpC4 with the mother filament subunits M6 and M7 (the interaction of ArpC2 with M5 is omitted for clarity). c The protrusion helix of ArpC1 fitted into its density close to subdomains 1 and 3 of M4. d Surface representation of the interactions of Arp3 and ArpC3 with the mother filament. Note the cavity below Arp2, where no contacts between the Arp2 subunit and the mother filament are observed. ArpC3 acts as a linker between Arp2 and the mother filament. e Surface representation of the interaction between Arp2, Arp3, and the first two subunits of the daughter filament.