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Molecular model of the outward facing state of the human P-glycoprotein (ABCB1), and comparison to a model of the human MRP5 (ABCC5).

Ravna AW, Sylte I, Sager G - Theor Biol Med Model (2007)

Bottom Line: In order to elucidate structural and molecular concepts of multidrug resistance, we have constructed a molecular model of the ATP-bound outward facing conformation of the human multidrug resistance protein ABCB1 using the Sav1866 crystal structure as a template, and compared the ABCB1 model with a previous ABCC5 model.The Sav1866 X-ray structure may serve as a suitable template for the ABCB1 model, as it did with ABCC5.The EPS in the substrate translocation chambers and the positive-negative ratio of charged amino acids were in accordance with the transport of cationic amphiphilic and lipophilic substrates by ABCB1, and the transport of organic anions by ABCC5.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Pharmacology, Institute of Medical Biology, University of Tromsø, N-9037 Tromsø, Norway. Aina.W.Ravna@fagmed.uit.no

ABSTRACT

Background: Multidrug resistance is a particular limitation to cancer chemotherapy, antibiotic treatment and HIV medication. The ABC (ATP binding cassette) transporters human P-glycoprotein (ABCB1) and the human MRP5 (ABCC5) are involved in multidrug resistance.

Results: In order to elucidate structural and molecular concepts of multidrug resistance, we have constructed a molecular model of the ATP-bound outward facing conformation of the human multidrug resistance protein ABCB1 using the Sav1866 crystal structure as a template, and compared the ABCB1 model with a previous ABCC5 model. The electrostatic potential surface (EPS) of the ABCB1 substrate translocation chamber, which transports cationic amphiphilic and lipophilic substrates, was neutral with negative and weakly positive areas. In contrast, EPS of the ABCC5 substrate translocation chamber, which transports organic anions, was generally positive. Positive-negative ratios of amino acids in the TMDs of ABCB1 and ABCC5 were also analyzed, and the positive-negative ratio of charged amino acids was higher in the ABCC5 TMDs than in the ABCB1 TMDs. In the ABCB1 model residues Leu65 (transmembrane helix 1 (TMH1)), Ile306 (TMH5), Ile340 (TMH6) and Phe343 (TMH6) may form a binding site, and this is in accordance with previous site directed mutagenesis studies.

Conclusion: The Sav1866 X-ray structure may serve as a suitable template for the ABCB1 model, as it did with ABCC5. The EPS in the substrate translocation chambers and the positive-negative ratio of charged amino acids were in accordance with the transport of cationic amphiphilic and lipophilic substrates by ABCB1, and the transport of organic anions by ABCC5.

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Ligand interaction areas. Close-up of putative ligand interaction areas of ABCB1 (Panel A) and ABCC5 (Panel B). The view is a cross-section of the transporters perpendicular to the membrane. The oval shaped object with the text "Verapamil" (Panel A) indicates where Verapamil binding may take place. TMHs are shown as blue Cα traces. Color coding of displayed residues: Carbon: White; Hydrogen: Grey; Oxygen: Red; Nitrogen: Blue. Panel A: Residues Leu65 (TMH1) [30], Ile306 (TMH5) [30], Ile340 (TMH6) [25, 30] and Phe343 (TMH6) [26] have been shown to interact with ligands in site directed mutagenesis studies. Panel B: Corresponding residues in ABCC5 are Gln190 (TMH1), Val410 (TMH5), Asn441 (TMH6) and Thr444 (TMH6) respectively.
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Figure 4: Ligand interaction areas. Close-up of putative ligand interaction areas of ABCB1 (Panel A) and ABCC5 (Panel B). The view is a cross-section of the transporters perpendicular to the membrane. The oval shaped object with the text "Verapamil" (Panel A) indicates where Verapamil binding may take place. TMHs are shown as blue Cα traces. Color coding of displayed residues: Carbon: White; Hydrogen: Grey; Oxygen: Red; Nitrogen: Blue. Panel A: Residues Leu65 (TMH1) [30], Ile306 (TMH5) [30], Ile340 (TMH6) [25, 30] and Phe343 (TMH6) [26] have been shown to interact with ligands in site directed mutagenesis studies. Panel B: Corresponding residues in ABCC5 are Gln190 (TMH1), Val410 (TMH5), Asn441 (TMH6) and Thr444 (TMH6) respectively.

Mentions: Site directed mutagenesis studies on ABCB1 have proposed a verapamil binding site including residues Leu65 (TMH1) [31], Ile306 (TMH5) [31], Ile340 (TMH6) [26,31] and Phe343 (TMH6) [27]. In the ABCB1 model these residues may form a binding site (Figure 4A). Ligand interactions between the TMH6 residues Ile340 and Phe343 and rhodamine have also been proposed in an ABCB1 modeling and docking study [33]. The corresponding residues in ABCC5 are Gln190 (TMH1), Val410 (TMH5), Asn441 (TMH6) and Thr444 (TMH6), respectively (Figure 4B). Gln190 (TMH1), Asn441 (TMH6) and Thr444 (TMH6) of ABCC5 have previously been proposed to take part in ligand binding in a previous MRP5 modeling and cGMP docking study (submitted). Interestingly, the above mentioned ABCB1 residues are more lipophilic than the corresponding ABCC5 residues. This is in accordance with the lipophilic efflux featured by ABCB1, and with the more neutral EPS of the ABCB1 substrate translocation chambers.


Molecular model of the outward facing state of the human P-glycoprotein (ABCB1), and comparison to a model of the human MRP5 (ABCC5).

Ravna AW, Sylte I, Sager G - Theor Biol Med Model (2007)

Ligand interaction areas. Close-up of putative ligand interaction areas of ABCB1 (Panel A) and ABCC5 (Panel B). The view is a cross-section of the transporters perpendicular to the membrane. The oval shaped object with the text "Verapamil" (Panel A) indicates where Verapamil binding may take place. TMHs are shown as blue Cα traces. Color coding of displayed residues: Carbon: White; Hydrogen: Grey; Oxygen: Red; Nitrogen: Blue. Panel A: Residues Leu65 (TMH1) [30], Ile306 (TMH5) [30], Ile340 (TMH6) [25, 30] and Phe343 (TMH6) [26] have been shown to interact with ligands in site directed mutagenesis studies. Panel B: Corresponding residues in ABCC5 are Gln190 (TMH1), Val410 (TMH5), Asn441 (TMH6) and Thr444 (TMH6) respectively.
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Figure 4: Ligand interaction areas. Close-up of putative ligand interaction areas of ABCB1 (Panel A) and ABCC5 (Panel B). The view is a cross-section of the transporters perpendicular to the membrane. The oval shaped object with the text "Verapamil" (Panel A) indicates where Verapamil binding may take place. TMHs are shown as blue Cα traces. Color coding of displayed residues: Carbon: White; Hydrogen: Grey; Oxygen: Red; Nitrogen: Blue. Panel A: Residues Leu65 (TMH1) [30], Ile306 (TMH5) [30], Ile340 (TMH6) [25, 30] and Phe343 (TMH6) [26] have been shown to interact with ligands in site directed mutagenesis studies. Panel B: Corresponding residues in ABCC5 are Gln190 (TMH1), Val410 (TMH5), Asn441 (TMH6) and Thr444 (TMH6) respectively.
Mentions: Site directed mutagenesis studies on ABCB1 have proposed a verapamil binding site including residues Leu65 (TMH1) [31], Ile306 (TMH5) [31], Ile340 (TMH6) [26,31] and Phe343 (TMH6) [27]. In the ABCB1 model these residues may form a binding site (Figure 4A). Ligand interactions between the TMH6 residues Ile340 and Phe343 and rhodamine have also been proposed in an ABCB1 modeling and docking study [33]. The corresponding residues in ABCC5 are Gln190 (TMH1), Val410 (TMH5), Asn441 (TMH6) and Thr444 (TMH6), respectively (Figure 4B). Gln190 (TMH1), Asn441 (TMH6) and Thr444 (TMH6) of ABCC5 have previously been proposed to take part in ligand binding in a previous MRP5 modeling and cGMP docking study (submitted). Interestingly, the above mentioned ABCB1 residues are more lipophilic than the corresponding ABCC5 residues. This is in accordance with the lipophilic efflux featured by ABCB1, and with the more neutral EPS of the ABCB1 substrate translocation chambers.

Bottom Line: In order to elucidate structural and molecular concepts of multidrug resistance, we have constructed a molecular model of the ATP-bound outward facing conformation of the human multidrug resistance protein ABCB1 using the Sav1866 crystal structure as a template, and compared the ABCB1 model with a previous ABCC5 model.The Sav1866 X-ray structure may serve as a suitable template for the ABCB1 model, as it did with ABCC5.The EPS in the substrate translocation chambers and the positive-negative ratio of charged amino acids were in accordance with the transport of cationic amphiphilic and lipophilic substrates by ABCB1, and the transport of organic anions by ABCC5.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Pharmacology, Institute of Medical Biology, University of Tromsø, N-9037 Tromsø, Norway. Aina.W.Ravna@fagmed.uit.no

ABSTRACT

Background: Multidrug resistance is a particular limitation to cancer chemotherapy, antibiotic treatment and HIV medication. The ABC (ATP binding cassette) transporters human P-glycoprotein (ABCB1) and the human MRP5 (ABCC5) are involved in multidrug resistance.

Results: In order to elucidate structural and molecular concepts of multidrug resistance, we have constructed a molecular model of the ATP-bound outward facing conformation of the human multidrug resistance protein ABCB1 using the Sav1866 crystal structure as a template, and compared the ABCB1 model with a previous ABCC5 model. The electrostatic potential surface (EPS) of the ABCB1 substrate translocation chamber, which transports cationic amphiphilic and lipophilic substrates, was neutral with negative and weakly positive areas. In contrast, EPS of the ABCC5 substrate translocation chamber, which transports organic anions, was generally positive. Positive-negative ratios of amino acids in the TMDs of ABCB1 and ABCC5 were also analyzed, and the positive-negative ratio of charged amino acids was higher in the ABCC5 TMDs than in the ABCB1 TMDs. In the ABCB1 model residues Leu65 (transmembrane helix 1 (TMH1)), Ile306 (TMH5), Ile340 (TMH6) and Phe343 (TMH6) may form a binding site, and this is in accordance with previous site directed mutagenesis studies.

Conclusion: The Sav1866 X-ray structure may serve as a suitable template for the ABCB1 model, as it did with ABCC5. The EPS in the substrate translocation chambers and the positive-negative ratio of charged amino acids were in accordance with the transport of cationic amphiphilic and lipophilic substrates by ABCB1, and the transport of organic anions by ABCC5.

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