Abstract
The human ATP-binding cassette transporter ABCB1 (P-glycoprotein, P-gp, MDR1), which is strongly related to multidrug resistance, is known for its high polyspecificity, thus binding a large number of structurally diverse molecules. The molecular basis of this polyspecificity in terms of binding site(s) is still not resolved and proposals range from a huge binding zone to up to seven distinct drug binding sites that are partly overlapping. Nevertheless, mutagenesis studies and photoaffinity labeling showed that transmembrane (TM) helices 1, 3, 11 and 12, as well as 5, 6, 7 and 8 are involved in ligand binding [1, 2].