Fig. 2.
Lipid-binding pocket and TM arrangement in BceB. (A) Zoomed-in view of the lipid-binding pocket outlined with a dotted box in (B). Individual TM helices are labeled, along with specific residue side chains lining the lipid-binding pocket. The cryo-EM map encompassing AUP is shown as a transparent gray surface. The hydrophilic headgroup of the lipid is positioned directly beneath the extracellular domain. (B) Overall atomic model of BceAB in a nucleotide-free conformation, showing an asymmetric arrangement of BceA subunits and the protrusion of the large extracellular domain above TM5–10. (C) Sliced view from the extracellular space of the TM helix arrangement observed in BceB. Binding of AUP (magenta sticks inside gray mesh) is clearly observed between TM5,6 and TM7,9.