title: Investigating the dynamic nature of the ABC transporters: ABCB1 and MsbA as examples for the potential synergies of MD theory and EPR applications.
abstract: ABC transporters are primary active transporters found in all kingdoms of life. Human multidrug resistance transporter ABCB1, or P-glycoprotein, has an extremely broad substrate spectrum and confers resistance against chemotherapy drug treatment in cancer cells. The bacterial ABC transporter MsbA is a lipid A flippase and a homolog to the human ABCB1 transporter, with which it partially shares its substrate spectrum. Crystal structures of MsbA and ABCB1 have been solved in multiple conformations, providing a glimpse into the possible conformational changes the transporter could be going through during the transport cycle. Crystal structures are inherently static, while a dynamic picture of the transporter in motion is needed for a complete understanding of transporter function. Molecular dynamics (MD) simulations and electron paramagnetic resonance (EPR) spectroscopy can provide structural information on ABC transporters, but the strength of these two methods lies in the potential to characterise the dynamic regime of these transporters. Information from the two methods is quite complementary. MD simulations provide an all atom dynamic picture of the time evolution of the molecular system, though with a narrow time window. EPR spectroscopy can probe structural, environmental and dynamic properties of the transporter in several time regimes, but only through the attachment sites of an exogenous spin label. In this review the synergistic effects that can be achieved by combining the two methods are highlighted, and a brief methodological background is also presented.
authors.affiliation: Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstr. 13A, 1090 Vienna, Austria Fraser.MacMillan@uea.ac.uk thomas.stockner@meduniwien.ac.at.
authors.forename: Thomas
authors.initials: T
authors.lastname: Stockner
authors.affiliation: Henry Wellcome Unit for Biological EPR, School of Chemistry, University of East Anglia, NR4 7TJ, Norwich, UK.
authors.forename: Anna
authors.initials: A
authors.lastname: Mullen
authors.affiliation: Henry Wellcome Unit for Biological EPR, School of Chemistry, University of East Anglia, NR4 7TJ, Norwich, UK. Fraser.MacMillan@uea.ac.uk thomas.stockner@meduniwien.ac.at.
authors.forename: Fraser
authors.initials: F
authors.lastname: MacMillan
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000737:chemistry / Q000378:metabolism; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001692:Biological Transport; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D006801:Humans; D056004:Molecular Dynamics Simulation; D017434:Protein Structure, Tertiary; D015203:Reproducibility of Results
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; C079726:MsbA protein, Bacteria; D000255:Adenosine Triphosphate
keywords: ABCB1; DEER; EPR; MD simulations; MsbA; PELDOR; modelling; protein dynamics