SEMINAR

Understanding multidrug transporter function: the delicate balance between substrate specificity and transporter promiscuity

Abstract
Two key characteristics of the multidrug transporter P-glycoprotein are its substrate promiscuity and structural flexibility. P-glycoprotein transports over 200 endogenous and drug substrates and plays a central role in the development of multidrug resistance in cancer. While residues essential for transport and binding have been identified, the large-scale structural rearrangements that occur during its transport cycle have made it difficult to pinpoint the physical location, exact molecular composition and specificity of the any potential substrate binding site. Here molecular dynamics simulations are used to calculate the free energy profile for the binding of morphine, nicardipine Hoechst 33342, Rhodamine 123, paclitaxel, tariquidar and verapamil to P-glycoprotein. We show that morphine and nicardipine primarily interact with key residues implicated in binding and transport from mutational studies, binding at different but overlapping sites within the transmembrane pore. Furthermore, their permeation pathways were distinct, but involved overlapping sets of residues. The results indicate that the binding location and permeation pathways of morphine and nicardipine are not well separated and cannot be considered as unique. Similar trends are identified for other compounds investigated, allowing us to propose structural mechanisms for competitive and non-competitive binding of the substrates investigated. Our results are consistent with a range of experimental studies and provide a structural perspective for our understanding of substrate uptake and transport by P-glycoprotein.

BIOGRAPHY

2015-present: Rita Cornforth Fellow and Senior Lecturer, Research School of Chemistry, Australian National University
2012-2014: ARC DECRA Fellow and Lecturer, School of Chemistry and Molecular Biosciences and School of Mathematics and Physics, University of Queensland
2009-2011: University of Queensland Postdoctoral Fellow, School of Chemistry and Molecular Biosciences, University of Queensland
2005-2008: Canadian Institutes of Health Research Postdoctoral Fellow, Department of Biological Sciences, University of Calgary, Canada
2005: PhD, Research School of Physics and Engineering, Australian National University

Research Fields and Interests:

Recent advances in membrane protein crystallography have provided tremendous insights into protein structure and function, however gaps remain in our understanding of the synergistic interactions between proteins, lipids and ligand molecules that contribute to biological function. This is particularly true for membrane protein structures. We incorporate both physiological and crystallographic conditions, and sparse experimental datasets into molecular dynamics simulations to examine the conformational dynamics of a protein in response to its environment. These dynamic interactions allow us to characterise the change in protein conformation on a ns to m timescale, providing a dynamic link between protein structure and biological function.

Selected Publications:

Subramanian, N., K. Condic-Jurkic, A.E. Mark, M.L. O'Mara. (2015) Identification of Possible Binding Sites for Morphine and Nicardipine on the Multidrug Transporter P-Glycoprotein Using Umbrella Sampling Techniques. J. Chem. Inf. Model. 55, 1202–1217

O’Mara, M.L. and AE Mark. (2014) Structural characterization of two metastable ATP-bound states of P-glycoprotein. PLoS One 9:e91916

Brooks, A.J., W. Dai, M.L. O’Mara, D. Abankwa, Y. Chhabra, R.A. Pelekanos, O. Gardon, K.A. Tunny, K.M. Blucher, C.J. Morton, M.W. Parker, E. Sierecki, Y. Gambin, K. Alexandrov, I.A. Wilson, M. Doxastakis, A.E. Mark, M.J. Waters. (2014) A new cytokine receptor activation paradigm: activation of JAK2 by the growth hormone receptor. Science 344, 1249783

Couñago, R.M., M.P. Ween, S.L. Begg, M. Bajaj, J. Zuegg, M.L. O’Mara, M.A. Cooper, A.G. McEwan, J.C. Paton, B. Kobe, C.A. McDevitt. (2013) Imperfect coordination chemistry facilitates metal ion release in the Psa permease. Nature Chem. Biol. 10, 35–41

O’Mara, M.L. and A.E. Mark. (2012) The effect of environment on the structure of a membrane protein: P-glycoprotein under physiological conditions. J Chem. Theor. Comput. 8, 3964-3976.