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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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ABCB1 and ABCC5 models. Cα traces of the ABCB1 (Panel A) and ABCC5 (Panel B) models viewed in the membrane plane, with the extracellular side facing upwards. Color code of the models is blue via white to red from N-terminal to C-terminal.
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Figure 2: ABCB1 and ABCC5 models. Cα traces of the ABCB1 (Panel A) and ABCC5 (Panel B) models viewed in the membrane plane, with the extracellular side facing upwards. Color code of the models is blue via white to red from N-terminal to C-terminal.

Mentions: The refined ABCB1 and ABCC5 (submitted) models are shown in Figure 2, panels A and B. The loop connecting NBD1 and TMD2 of ABCB1 was mainly α-helical from residues 623–703, except from a parallel β-sheet formed between residues 614–618 and residues 646–650, and an extended stretch from residues 651–657. The first part of this loop was folded and covering NBD1 of ABCB1 towards the cytoplasm. A central cavity perpendicular to the cell membrane was formed by TMD1 and TMD2, and TMHs 1, 2, 3, 5, 6, 7, 8, 9, 11 and 12 contributed to the cavity lining. TMH5 and TMH2 of TMD1 were packed against TMH8 and TMH11 of TMD2, respectively, with mainly hydrophobic interactions. The substrate translocation chamber was closed towards the intracellular side, and the TMDs were twisted relative to the NBDs. The TMHs diverged into two symmetrical parts towards the extracellular side, one part consisting of TMHs 1 and 2 of TMD1 and TMHs 9–12 of TMD2, and one part consisting of TMHs 7 and 8 of TMD2 and TMHs 3–6 of TMD1 (Figure 2). Interactions between the NBDs were relatively hydrophilic, and the secondary structure of the areas of each NBD forming the contact area between the two NBDs was generally in extended conformation. The NBDs, having the same fold as the NBDs of the Sav1866 crystal structure, were tightly packed at the intracellular side of the membrane, containing the nucleotide binding sites formed by the motifs Walker A, Walker B, Q-loop and switch regions.


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)

ABCB1 and ABCC5 models. Cα traces of the ABCB1 (Panel A) and ABCC5 (Panel B) models viewed in the membrane plane, with the extracellular side facing upwards. Color code of the models is blue via white to red from N-terminal to C-terminal.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2211457&req=5

Figure 2: ABCB1 and ABCC5 models. Cα traces of the ABCB1 (Panel A) and ABCC5 (Panel B) models viewed in the membrane plane, with the extracellular side facing upwards. Color code of the models is blue via white to red from N-terminal to C-terminal.
Mentions: The refined ABCB1 and ABCC5 (submitted) models are shown in Figure 2, panels A and B. The loop connecting NBD1 and TMD2 of ABCB1 was mainly α-helical from residues 623–703, except from a parallel β-sheet formed between residues 614–618 and residues 646–650, and an extended stretch from residues 651–657. The first part of this loop was folded and covering NBD1 of ABCB1 towards the cytoplasm. A central cavity perpendicular to the cell membrane was formed by TMD1 and TMD2, and TMHs 1, 2, 3, 5, 6, 7, 8, 9, 11 and 12 contributed to the cavity lining. TMH5 and TMH2 of TMD1 were packed against TMH8 and TMH11 of TMD2, respectively, with mainly hydrophobic interactions. The substrate translocation chamber was closed towards the intracellular side, and the TMDs were twisted relative to the NBDs. The TMHs diverged into two symmetrical parts towards the extracellular side, one part consisting of TMHs 1 and 2 of TMD1 and TMHs 9–12 of TMD2, and one part consisting of TMHs 7 and 8 of TMD2 and TMHs 3–6 of TMD1 (Figure 2). Interactions between the NBDs were relatively hydrophilic, and the secondary structure of the areas of each NBD forming the contact area between the two NBDs was generally in extended conformation. The NBDs, having the same fold as the NBDs of the Sav1866 crystal structure, were tightly packed at the intracellular side of the membrane, containing the nucleotide binding sites formed by the motifs Walker A, Walker B, Q-loop and switch regions.

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.

Show MeSH