Chapter Three - Molecular Basis of the Polyspecificity of P-Glycoprotein (ABCB1): Recent Biochemical and Structural Studies
Introduction
ATP-binding cassette (ABC) transporters such as ABCB1 (P-glycoprotein/P-gp), ABCG2, and ABCC1 are well known for their association with multidrug resistance (MDR), effluxing structurally diverse compounds, powered by the hydrolysis of ATP (Ambudkar et al., 1999). P-gp also plays an important role in the pharmacokinetics of many drugs, altering their absorption, distribution, and excretion. P-gp has been extensively studied since 1976, when it was identified as the multidrug efflux pump in Chinese hamster ovary cells that had been selected for resistance to colchicine (Juliano & Ling, 1976). It is a 170 kDa single polypeptide chain consisting of two transmembrane domains (TMDs) and two nucleotide-binding domains (NBDs). It is believed that this transporter functions through an alternate access mechanism involving two different conformations (Hollenstein et al., 2007, Jardetzk, 1966, Senior et al., 1995, van Wonderen et al., 2014). Drug binding occurs when the protein adopts an inward-facing conformation (inverted V appearance) observed in P-gps such as those found in mouse and Caenorhabditis elegans P-gp X-ray structures obtained in the absence of nucleotide (Aller et al., 2009, Jin et al., 2012). This is followed by a significant structural change to an outward-facing conformation (V-shaped in appearance) such as the one exhibited by the X-ray structure of SAV1866 with bound nucleotide (ADP) (Dawson & Locher, 2006), when drug release takes place. Hydrolysis of ATP is believed to reset the protein to the inward-facing form to begin a new cycle of drug binding and release (Callaghan et al., 2006, Sauna and Ambudkar, 2000). The switch from inward to outward form certainly requires a highly flexible structure.
Substrate “promiscuity” or polyspecificity is a well-known characteristic of P-gp and the subject of much research. Attempts have been made to understand the ability of P-gp to recognize various chemically and structurally diverse substrates through biochemical investigations and structural studies. Despite all these studies, the molecular basis of this unusual property still remains poorly understood and is a matter of intense debate. Other review articles have been published recently on the subject (Gutmann et al., 2010, Sharom, 2014, Wong et al., 2014). In this review, we will focus on recent biochemical and structural studies of P-gp, with discussion primarily on its substrate polyspecificity.
Section snippets
Structural flexibility revealed by X-ray crystallography
In 2009, Aller et al. (2009) were the first to report an X-ray structure of a mammalian ABC transporter. They solved the structure of mouse P-gp at a resolution of 3.8–4.4 Å, in the absence of nucleotide, with and without bound inhibitors. In the absence of nucleotide or drug-substrate, the mouse P-gp structure (3G5U.pdb) was observed to adopt an inward-facing conformation. It has a large internal cavity of about 6000 Å3 open to both the cytoplasm and the membrane inner leaflet, with a wide
Molecular Modeling Studies
Since the publication of the first X-ray crystal structures of mouse P-gp in 2009 (Aller et al., 2009), a number of laboratories have employed molecular modeling studies trying to identify the drug-binding sites of P-gp. The high similarity between mouse (mdr1a) and human P-gp sequences (87% identity, 94% similarity) has encouraged many research groups to build homology models of human P-gp based on the structures of mouse P-gp and many modeling studies have been published. In 2012, the
Conclusions and Perspectives
The ability of P-gp to recognize a wide variety of substrates is remarkable and thus it has been the subject of intense research for almost 40 years. The field has certainly shown advances, as we know today (i) the overall molecular structure of P-gp, (ii) the structure is highly flexible, (iii) the substrates are transported through a central cavity, and (iv) the alternate access mechanism of transport that enjoys a significant consensus in the ABC transporter community. It seems evident that
Acknowledgments
We thank George Leiman for editorial assistance in the preparation of the chapter and the Intramural Research Program of the National Institutes of Health, National Cancer Institute, Center for Cancer Research, for financial support. H.-M. S. was supported in part by a NUS-OPF fellowship from the National University of Singapore. A critical reading of the chapter by Drs. John Golin and Atish Patel is also gratefully acknowledged.
References (78)
- et al.
Relation between the turnover number for vinblastine transport and for vinblastine-stimulated ATP hydrolysis by human P-glycoprotein
Journal of Biological Chemistry
(1997) - et al.
The power of the pump: Mechanisms of action of P-glycoprotein (ABCB1)
European Journal of Pharmaceutical Sciences
(2006) - et al.
The translocation mechanism of P-glycoprotein
FEBS Letters
(2006) Major photoaffinity drug labeling sites for iodoaryl azidoprazosin in P-glycoprotein are within, or immediately C-terminal to, transmembrane domains 6 and 12
Journal of Biological Chemistry
(1993)- et al.
Understanding polyspecificity of multidrug ABC transporters: Closing in on the gaps in ABCB1
Trends in Biochemical Sciences
(2010) - et al.
Structure and mechanism of ABC transporter proteins
Current Opinion in Structural Biology
(2007) - et al.
A surface glycoprotein modulating drug permeability in Chinese hamster ovary cell mutants
Biochimica et Biophysica Acta
(1976) - et al.
Correlation between steady-state ATP hydrolysis and vanadate-induced ADP trapping in human P-glycoprotein. Evidence for ADP release as the rate-limiting step in the catalytic cycle and its modulation by substrates
Journal of Biological Chemistry
(2001) - et al.
Permanent activation of the human P-glycoprotein by covalent modification of a residue in the drug-binding site
Journal of Biological Chemistry
(2003) - et al.
Substrate-induced conformational, changes in the transmembrane segments of human P-glycoprotein—Direct evidence for the substrate-induced fit mechanism for drug binding
Journal of Biological Chemistry
(2003)
Human P-glycoprotein is active when the two halves are clamped together in the closed conformation
Biochemical and Biophysical Research Communications
Membrane topology of a cysteine-less mutant of human P-glycoprotein
Journal of Biological Chemistry
Identification of residues in the drug-binding site of human P-glycoprotein using a thiol-reactive substrate
Journal of Biological Chemistry
The transmembrane domains of the human multidrug resistance P- glycoprotein are sufficient to mediate drug binding and trafficking to the cell surface
Journal of Biological Chemistry
Identification of residues within the drug-binding domain of the human multidrug resistance P-glycoprotein by cysteine-scanning mutagenesis and reaction with dibromobimane
Journal of Biological Chemistry
The packing of the transmembrane segments of human multidrug resistance P-glycoprotein is revealed by disulfide cross-linking analysis
Journal of Biological Chemistry
Defining the drug-binding site in the human multidrug resistance P-glycoprotein using a methanethiosulfonate analog of verapamil, MTS-verapamil
Journal of Biological Chemistry
Location of the rhodamine-binding site in the human multidrug resistance P-glycoprotein
Journal of Biological Chemistry
P-glycoprotein models of the apo and ATP-bound states based on homology with Sav 1866 and MalK
FEBS Letters
P-glycoprotein, a gatekeeper in the blood-brain barrier
Advanced Drug Delivery Reviews
The catalytic cycle of P-glycoprotein
FEBS Letters
Peptide-transport by the multidrug resistance pump
Journal of Biological Chemistry
Human P-glycoprotein transports cortisol, aldosterone, and dexamethasone, but not progesterone
Journal of Biological Chemistry
Dynamic ligand-induced conformational rearrangements in P-glycoprotein as probed by fluorescence resonance energy transfer spectroscopy
Journal of Biological Chemistry
P-glycoprotein retains drug-stimulated ATPase activity upon covalent linkage of the two nucleotide binding domains at their C-terminal ends
Journal of Biological Chemistry
On the origin of large flexibility of P-glycoprotein in the inward-facing state
Journal of Biological Chemistry
Towards understanding promiscuity in multidrug efflux pumps
Trends in Biochemical Sciences
Structure of P-glycoprotein reveals a molecular basis for poly-specific drug binding
Science
Gapped BLAST and PSI-BLAST: A new generation of protein database search programs
Nucleic Acids Research
Biochemical, cellular, and pharmacological aspects of the multidrug transporter
Annual Review of Pharmacology and Toxicology
Predicting P-glycoprotein-mediated drug transport based on support vector machine and three-dimensional crystal structure of P-glycoprotein
PLoS One
A P-glycoprotein protects Caenorhabditis elegans against natural toxins
The EMBO Journal
Multiple transport-active binding sites are available for a single substrate on human P-glycoprotein (ABCB1)
PLoS One
Multispecificity of drug transporters: Probing inhibitor selectivity for the human drug efflux transporters ABCB1 and ABCG2
ChemMedChem
Structure of a bacterial multidrug ABC transporter
Nature
In silico prediction of substrate properties for ABC-multidrug transporters
Expert Opinion on Drug Metabolism & Toxicology
Evidence for two nonidentical drug-interaction sites in the human P-glycoprotein
Proceedings of the National Academy of Sciences of the United States of America
Predicting binding to P-glycoprotein by flexible receptor docking
PLoS Computational Biology
Pore-exposed tyrosine residues of P-glycoprotein are important hydrogen-bonding partners for drugs
Molecular Pharmacology
Cited by (115)
Overcoming multi drug resistance mediated by ABC transporters by a novel acetogenin- annonacin from Annona muricata L.
2024, Journal of EthnopharmacologyImpact of P-Glycoprotein-Mediated Drug-Endogenous Substrate Interactions on Androgen and Blood-Brain Barrier Permeability
2024, Journal of Pharmaceutical SciencesInteraction of A<inf>3</inf> adenosine receptor ligands with the human multidrug transporter ABCG2
2022, European Journal of Medicinal ChemistryPhytochemicals reverse P-glycoprotein mediated multidrug resistance via signal transduction pathways
2021, Biomedicine and Pharmacotherapy