Extended Data Fig. 4: Opening of the β-propeller gate of TcB.

a, Opening of the β-propeller gate is triggered by sensor loops. Side views of the closed, (left; before binding to TcA) (PDB 4O9X) and open (right; after binding to TcA) state of the TcA-binding six-bladed β-propeller domain of TcB–TcC. The structure of the closed state was structurally aligned with the structure of the open state and is shown together with the TcB-binding domain of TcA (middle). Note the clashing loops (sensor loops) between TcA (residues 2418–2430, green) and TcB (residues 527–536, orange). Colours correspond to those in Fig. 1. b, c, Effect of the ADP-ribosyltransferase on the structure of TcB–TcC. Crystal structures of unbound wild-type and empty TcB–TcC are shown in b. TcB–TcC structures obtained from the cryo-EM structures of ABC(WT) and ABC(D651A) are shown in c. For the structures of TcB–TcC(WT), the channel radius profile is shown as a function of distance along the channel axis before and after TcA binding in b and c, respectively (left). The narrowest constriction of the channel lumen towards the TcA-binding domain (constriction site) has a diameter of 10.5 Å in the open state. For all structures, the mesh surface of the computed channel along the cocoon interior is shown in yellow. Note that the presence or absence of the ADP-ribosyltransferase does not affect the channel profile in the unbound state of the cocoon b. Note also, that cocoons with cleaved (TcB–TcC(WT)) or uncleaved (TcB–TcC(D651A)) ADP-ribosyltransferase show an almost identical channel profile following binding to TcA (c). d, e, Comparison of crystal contacts in the structures of empty TcB–TcC and TcB–TcC(WT). Top and side views of the crystal structures of empty TcB–TcC (d) and TcB–TcC(WT) (PDB 4O9X) (e) including crystal contacts. The TcA-binding domain of TcB is indicated by a dashed box and coloured as in Fig. 1b, c. The gatekeeper hairpin (residues 514–524) is highlighted in red.