Figure 6. Inter-subunit interfaces of the XaxAB pore complex.

(a) Overview of four prominent inter-subunit interfaces. (b,c) The tail domain of XaxA forms an extensive putative hydrogen network with the tail and neck domain of the adjacent XaxB. (d) A putative salt bridge formed between the C-terminus and the loop connecting αC1 and αC2 of neighboring XaxA protomers further stabilizes the pore complex. (e) Stabilization of the transmembrane pore by additional putative hydrogen bonds and a salt bridge formed between XaxA and XaxB from the adjacent subunit. Protomers of XaxA and XaxB are depicted in green and yellow, respectively. Helices not involved in the interaction are shown in a lighter color for visualization purposes.