Extended Data Fig. 6: Unique relative displacement of NBDs in both the G907–LPS–EcMsbA and G092–LPS–EcMsbA complex crystal structures.

a–e, Structural superpositions of related B-family ABC transporters are provided in two orthogonal views, in which all structural superpositions were performed by aligning only the transmembrane portion of each subunit B protomer onto that of subunit A. In the case of CePgp, the C-terminal transmembrane region was superimposed onto the N-terminal transmembrane region. The structures are as follows: a, G907–LPS–EcMsbA; b, G092–LPS–EcMsbA; c, LPS–EcMsbA–cryo (PDB accession 5TV4); d, CePgp (PDB accession 4F4C); e, Thermus thermophilus TmrAB (PDB accession 5MKK). In comparing these structures, it is noteworthy that EcMsbA is a homodimeric transporter, whereas CePgp is a concatenated transporter, and TmrAB is a heterodimeric transporter; yet the structural similarity within all ‘self-pairs’ of transmembrane regions is high. Specifically, when excluding the NBDs from this analysis: a, Cα r.m.s.d. 1.26 Å; b, Cα r.m.s.d. 0.82 Å; c, Cα r.m.s.d. 1.09 Å; d, Cα r.m.s.d. 3.18 Å; e, Cα r.m.s.d. 1.66 Å. In contrast to the high structural correspondence observed between their superimposed or ‘self-paired’ transmembrane regions, the G907–LPS–EcMsbA and G092–LPS–EcMsbA complex structures both show a marked translational displacement of one NBD relative to the other, measuring up to 15 Å between equivalent Cα positions. It is notable that the extent and apparent vector of the structural translation observed at the level of the NBDs are unique to the inhibitor-bound EcMsbA complexes studied here. For reference, the three residues that constitute the highly conserved CH1–CH2–NBD coupling interaction network are shown in yellow sphere representation in all structures.