Abstract
P-glycoprotein (P-gp) exports a broad range of dissimilar compounds, including drugs, lipids and lipid-like molecules. Due to its substrate promiscuity, P-gp is a key player in the development of cancer multidrug resistance (MDR). Although P-gp is one of the most studied members of ABC-transporters, the mechanism of how its substrates access the cavity remains unclear. In this work, we performed coarse-grained (CG) molecular dynamics (MD) simulations to explore possible pathways of lipid-uptake in the inward-facing conformation of P-gp embedded in bilayers with different PC:PE lipid ratios. Our results show that in the inward facing orientation only lipids from the lower leaflet are taken up by the transporter. We identify positively charged residues at the portals of P-gp that favor lipid entrance to the cavity, as well as lipid binding sites, in good agreement with previous experimental studies. Our results show no selectivity for PC vs. PE lipids. We offer several examples of lipid uptake-pathways for PC and PE lipids that help to elucidate the molecular mechanism of substrate-uptake in P-gp.
