P-gp Lipid Uptake Pathways Determined by Coarse-Grain Molecular Dynamic Simulation

Abstract

P-glycoprotein (P-gp) belongs to the ATP-binding cassette transporters (ABC) superfamily of membrane proteins. The transport mechanism in ABC transporters is triggered by ATP binding and hydrolysis at cytosolic nucleotide binding domains (NBDs). NBDs dimerization and dissociation are coupled with conformational changes in the transmembrane domains (TMDs), which form the translocation pathway for the substrates. Due to its ability to recognize and pump drugs to the extracellular medium, P-gp is a key player in cancer multidrug resistance. Among its substrates are also lipids and lipid-like molecules, as, for example, miltelfosine, a phospholipid-based anticancer drug. For the development of strategies targeting P-gp inhibition, a better understanding of the steps involved in substrate recognition and uptake is needed. In this work, we use coarse-grain (CG) molecular dynamics (MD) simulations to explore possible pathways of lipid uptake in the inward-facing conformation of P-gp. Five different lipid environments were considered: a pure POPC bilayer, a pure POPE bilayer, a symmetrical POPC:POPE bilayer, and two additional bilayers with different ratios of POPE and POPC lipids. The simulations, each of the duration of 20μs, were carried out using the MARTINI force field. The results highlight the role of specific transmembrane helices and residues in the initial steps of the uptake and for the interactions established with a given lipid once inside the cavity. We suggest possible uptake pathways in P-gp in the different lipid environments used in this study.