Fig. 1: Conformational states of IrtAB.

a Domain organization of IrtAB. The siderophore interaction domain (SID, blue) is N-terminally positioned to IrtA (teal). IrtB (pink) forms a separate open reading frame. b Cryo-EM maps of full-length IrtAB reconstituted in nanodisc or purified in LMNG detergent. Inward-facing (IF) and outward-occluded (OF_occl) maps were determined from distinct datasets. At the periplasmic side of OF_occl IrtAB, a non-proteinaceous density (contoured at 6 σ) is observed, which likely corresponds to a phospholipid (nanodisc sample) or an LMNG molecule (detergent sample). The SID (blue density) was generally less well resolved. c The IF cavity is accessible from the inner leaflet of the lipid bilayer. The OF_occl conformation features a large cavity that is sealed from both sides of the membrane. In the OF_occl conformation, a lateral membrane-facing crevice spanning across the whole lipid bilayer is formed between TMH2^IrtA and TMH5^IrtB.