Extended Data Fig. 8|. Flattening causes changes in the barbed end groove that facilitate long pitch interactions with actin subunits.

a, Molecular surface representation of active Arp3 showing perspective of close up views of the barbed end grooves (BEGs) depicted in b. b, BEG of inactive (PDB 4JD2) or active Arp2 or Arp3 with engaged D-loop from actin subunit n+1 or n. Residue numbers in left panels are for the S. pombe Arp2/3 complex. Green spheres and dashed line show distance x₃, which measures the distance between the C-terminus and the front of the BEG. c, Plot of the twist angle versus distance x₃ for inactive or active structures of actin, Arp2 or Arp3. Individually labeled data points are as described in Extended Data Fig. 7d.