Extended Data Fig. 3. Alignment of barbed-end subunit structures with previously determined actin structures.

a, Superimposition of the A₂ subunit of the barbed end structure (colored dark-red) with the structure of ADP-bound filamentous α-actin (pdb 8a2t, colored green). b, Superimposition of the A₂ subunit of the barbed end structure with the structure of ATP-bound monomeric α-actin (pdb 2v52, colored pink). c, Superimposition of the A₀ subunit of the barbed end structure (colored orange) with the structure of ATP-bound monomeric α-actin (pdb 2v52). d, Superimposition of the A₂ (colored dark-red) and A₁ (colored salmon) subunits of the barbed end structure. The only observed change in penultimate subunit A₁ is a small rearrangement of the W-loop. This change in the W-loop is expected, because this region would interact with the D-loop of the missing subunit. e, Zoom of the R177-N111S backdoor as seen from the F-actin exterior for the A₂ and A₁ subunits of the barbed end structure. Amino acids that form the backdoor are annotated. Phalloidin is hidden for clarity. Although the subunits adopt the ADP state, P_i from pdb 8a2s (F-actin in the Mg²⁺-ADP-P_i state) is shown semi-transparently to emphasize the P_i-binding site. f, Architecture of the P_i-release backdoor in structures of ADP-bound F-actin (left), the ADP-bound A₂ subunit at the F-actin barbed end (middle-left), the ADP-bound A₀ subunit at the F-actin barbed end (middle-right) and ATP-bound G-actin (right).