Apolipoprotein E-mediated binding of hypertriglyceridemic very low density lipoproteins to isolated low density lipoprotein receptors detected by ligand blotting

HTG-VLDL₁, like LDL, bind with high affinity to electrophoretically transferred, isolated LDL receptors partially purified from bovine adrenal glands. Ligand blotting techniques show that binding is calcium dependent; little or no binding of LDL or HTG-VLDL₁ is observed in the presence of 10 mM EDTA. HTG-VLDL₁ does not bind in the presence of 7 mM suramin, an inhibitor of LDL binding to the LDL receptor. Pretreatment of LDL with either thrombin or trypsin does not affect apoB-mediated LDL binding to the LDL receptor. ApoE-mediated binding of HTG-VLDL₁ to the blotted LDL receptor is abolished or greatly decreased by thrombin treatment of HTG-VLDL₁ trypsin treatment of HTG-VLDL₁ abolishes binding. Reincorporation of apoE into trypsinized HTG-VLDL₁ restores binding. These studies demonstrate unequivocally that HTG-VLDL₁ bind to the LDL receptor, that the binding of HTG-VLDL₁ to the isolated LDL receptor is mediated through the thrombin-accessible apoE, and that HTG-VLDL₁ which bind via potentially dissociable apoE rather than non-tranferable apoB can be used for ligand blotting.