PT  - JOURNAL ARTICLE
AU  - Karin Pleban
AU  - Stephan Kopp
AU  - Edina Csaszar
AU  - Michael Peer
AU  - Thomas Hrebicek
AU  - Andreas Rizzi
AU  - Gerhard F. Ecker
AU  - Peter Chiba
TI  - P-Glycoprotein Substrate Binding Domains Are Located at the Transmembrane Domain/Transmembrane Domain Interfaces: A Combined Photoaffinity Labeling-Protein Homology Modeling Approach
AID  - 10.1124/mol.104.006973
DP  - 2005 Feb 01
TA  - Molecular Pharmacology
PG  - 365--374
VI  - 67
IP  - 2
4099  - http://molpharm.aspetjournals.org/content/67/2/365.short
4100  - http://molpharm.aspetjournals.org/content/67/2/365.full
SO  - Mol Pharmacol2005 Feb 01; 67
AB  - P-glycoprotein (P-gp) is an energy-dependent multidrug efflux pump conferring resistance to cancer chemotherapy. Characterization of the mechanism of drug transport at a molecular level represents an important prerequisite for the design of pump inhibitors, which resensitize cancer cells to standard chemotherapy. In addition, P-glycoprotein plays an important role for early absorption, distribution, metabolism, excretion, and toxicity profiling in drug development. A set of propafenonetype substrate photoaffinity ligands has been used in this study in conjunction with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to define the substrate binding domain(s) of P-gp in more detail. The highest labeling was observed in transmembrane segments 3, 5, 8, and 11. A homology model for P-gp was generated on the basis of the dimeric crystal structure of Vibrio cholerae MsbA, an essential lipid transporter. Thereafter, the labeling pattern was projected onto the 3D atomic-detail model of P-gp to allow a visualization of the binding domain(s). Labeling is predicted by the model to occur at the two transmembrane domain/transmembrane domain interfaces formed between the amino- and carboxyl-terminal half of P-gp. These interfaces are formed by transmembrane (TM) segments 3 and 11 on one hand and TM segments 5 and 8 on the other hand. Available data on LmrA and AcrB, two bacterial multidrug efflux pumps, suggest that binding at domain interfaces may be a general feature of polyspecific drug efflux pumps.