Branching actin filaments drive cell motion, enabling for example the wiring of the human nervous system. A seven protein complex called ARP2/3 (light and dark blue) attaches to the side of an existing actin filament (orange) forming the base of a branch filament. Two proteins in the ARP2/3 complex (dark blue) are similar to actin monomers and are positioned as the first two monomers of the branch. PDB identifiers 1atn (actin monomer), 1alm (actin filament), 1k8k (ARP2/3 complex).
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