Fig. 6

Structure of the Ah TssA2^A CTD ring. a Negative stain EM particle averaging of Ah TssA2^A CTD indicating five-fold symmetry. b Structure of 10 Ah TssA2^A CTD monomers assembled to form a decameric oligomer exhibiting D₅ symmetry (PDB: 6G7C https://www.ebi.ac.uk/pdbe/entry/pdb/6g7c). Boxed region 1 (Interface 1), two-fold axis formed by dimerisation via the WEP motif (red and blue chains). Boxed region 2 (Interface 2), two-fold axis generated through packing of helices α9, α10 and α11 (blue and orange chains). The N-terminus of chain A is indicated and the dimensions of the ring are shown. c Interface 1 with key interacting residues indicated (chain A, pink: chain B, light blue). d Side view of interface 2 with interacting surfaces highlighted in light blue and sand. e Superposition of WEP-mediated dimers from Ah TssA2^A (cyan) and EAEC TssA2^B (PDB: 4YO5, green) about the WEP interface. The monomers exhibit a different relative orientation of ~35° about the WEP interface. View corresponds to chains A and B shown in (b). f Structural similarity of the CTD monomers of Ah TssA2^A (cyan) and EAEC TssA2^B (PDB: 4YO5, green). Helices α13 and α14 are unique to EAEC TssA2^B and form the C-terminal extension (magenta), which is important for the different quaternary structures assembled by TssA2^A and TssA2^B. g, h Side by side views of the Ah TssA2^A (g) and EAEC TssA2^B (h) CTD oligomers with their respective five-fold and six-fold axes vertical. Assembly of Ah TssA2^A WEP-mediated dimers (cyan) around the five-fold axis involves a rotation relative to EAEC TssA2^B (green) of ~50° around the dimer axis as illustrated by the dotted black line. The neighbouring subunits with which each monomer within a WEP-mediated dimer interacts are shown in grey