Lipid Binding and Lipid-Uptake in P-Glycoprotein: Comparison of the Inward- and Outward-Facing Conformation

Abstract

P-glycoprotein (Pgp) belongs to the ABC transporters superfamily. The ATP hydrolysis at its nucleotide binding domains (NBD) triggers conformational changes of the transmembrane domains (TMD), enabling the translocation of substrates to the extracellular medium. Pgp translocates a wide range of chemically diverse substrates, ranging from toxins to drugs, lipids and lipid-like molecules, and prevents the accumulation of chemotherapy agents inside the cell. This makes Pgp a key player in cancer multidrug resistance (MDR). Methods that allow the study of drug and lipid binding and uptake at the molecular level will contribute, in the long term, to the development of new drugs to inhibit substrate translocation, and therefore improve chemotherapy treatments. In this work, we perform coarse-grained (CG) molecular dynamics (MD) simulations of Pgp embedded in a symmetric POPC:POPE bilayer to investigate the lipid-uptake of Pgp in the inward- (PgpIN) and outward-facing (PgpOUT) conformation. These 20μs long simulations allow the characterization of lipid-binding sites in the two conformations, and the description, at the molecular level, of lipid-uptake events. To accounts for the effects of cholesterol, we consider a second set of simulations of PgpIN and PgpOUT in a symmetric PC:PE:CHOL bilayer. Our results highlight how lipid-uptake is influenced by CHOL molecules located at the surface of the Pgp.