Identification of the domains of photoincorporation of the 3'- and 7- benzophenone analogues of taxol in the carboxyl-terminal half of murine mdr1b P-glycoprotein

P-glycoprotein is an ATP-dependent drug-efflux pump that can transport a diverse range of structurally and functionally unrelated hydrophobic compounds across the plasma membrane. The transporter is composed of two homologous halves, each containing a nucleotide binding fold and six putative transmembrane spanning segments. The contact domains between the murine mdr1b P-glycoprotein and two photoreactive Taxol analogues have been mapped by a combination of CNBr digestion and immunoprecipitation studies. We had demonstrated previously that the 3‘-p-benzoyldihydrocinnamoyl (BzDC) analogue of Taxol specifically photolabeled mdr1b P-glycoprotein and now show that the corresponding C-7 analogue likewise specifically photoincorporates into the transporter. CNBr digestion of both photolabeled P-glycoproteins gave rise to an approximate 10 kDa tritium-labeled peptide, each of which was a distinct polypeptide. The CNBr fragment generated from the 3‘-BzDC-Taxol-photolabeled P-glycoprotein was immunoprecipitated by ...