The multidrug efflux transporter ABCG2 (also known as Breast Cancer Resistance Protein) is a critical target in overcoming chemotherapy resistance. It has long been known that ABCG2 activity is dependent on the presence of membrane cholesterol. While CryoEM structures and mutagenic studies have revealed some potential cholesterol binding sites, the mechanistic basis for cholesterol modulation of ABCG2 transport remains elusive.
One hypothesis is that cholesterol binding preferentially stabilizes particular stages in the ABCG2 conformational cycle. To investigate this possibility, we have performed coarse-grained molecular dynamics simulation of ABCG2 in three inward facing conformations (an inhibitor bound conformation, an ATB bound conformation, and an apo closed conformation), embedded in a model of an average plasma membrane to quantify the unique lipid fingerprint of the transporter. These simulations revealed a clear pattern of interaction with membrane lipids shared between the three inward facing conformations, with two hotspots for ABCG2/cholesterol interaction within the extracellular leaflet.
By quantifying the dynamics of cholesterol binding to ABCG2, and the influence of the local membrane environment on the efflux of chemotherapeutics, we aim to identify the how membrane microdomain composition and cholesterol concentration are coupled to ABCG2 transport rates.