Fig. 4.

Schematic representation of the homology models of BCRP. A, the substrate-unbound nucleotide-free inward-facing open apo conformation based on the MsbA structure (PDB code 3B5W); B, the substrate-bound nucleotide-free inward-facing closed apo conformation based on the mouse P-gp structure (PDB code 3G60). The approximate locations of several amino acid residues in the MSD (Ser⁴⁴¹, Glu⁴⁴⁶, His⁴⁵⁷, Phe⁴⁸⁹, and Arg⁴⁸²) or the NBD (Lys⁸⁶ and Glu²¹¹) that could be important for substrate specificity and/or overall transport activity are indicated; C, the nucleotide-bound outward-facing conformation based on the Sav1866 structure (PDB code 2HYD). Two monomers in the BCRP dimer are shown in different colors.