Apolipoprotein E isoform-specific binding to the low-density lipoprotein receptor

Apolipoprotein E (apoE) is a ligand for members of the low-density lipoprotein receptor (LDLR) family and functions in plasma cholesterol homeostasis. A fluorescence-based assay has been employed in molecular studies of receptor–ligand interactions. Competition experiments revealed isoform-specific differences in binding of lipid-associated apoE N terminal (NT) domain to a recombinant soluble LDLR (sLDLR). In a similar manner, lipid-associated—but not lipid-free—full-length apoE3 showed binding activity to sLDLR. The molecular chaperone, receptor-associated protein, inhibited apoE3–NT–phospholipid complex binding to sLDLR. Kinetic studies of apoE3–NT–phospholipid complex interaction with sLDLR revealed time-dependent effects of apoE–NT isoform binding to sLDLR. The results reveal a discerning method for study of the molecular basis of ligand interactions that likely influence receptor function in maintenance of whole body cholesterol homeostasis.