fig2

Figure 2. Amino acid residues with HBD side chains of ABCB1 at the level of the membrane (NBDs are truncated). (A) Abcb1a structure of the apo conformation open to the cytosol (PDB entry 4m1m) (side view). (B) Model of the closed conformation, based on the crystal structure of Sav1866 with two nucleotides bound (PDB entry 2hyd) (side view). (C) Apo conformation (top view). (D) Model of the closed conformation (top view). Amino acid side chains with HBDs are shown. TMD6 and TMD12 are colored yellow, whereas other helices are colored light gray. The two dashed lines indicate the position of the membrane (adapted from Ref.^[67], for details see Supplementary Figure 1A and B).