Isolation and characterization of the apolipoprotein E receptor from canine and human liver.
Previous results have demonstrated that liver membranes possess two distinct lipoprotein receptors: a low density lipoprotein (LDL) receptor that binds lipoproteins containing either apolipoprotein (apo-) B or apo-E, and an apo-E-specific receptor that binds apo-E-containing lipoproteins, but not the apo-B-containing LDL. This study reports the isolation and purification of apo-B,E(LDL) and apo-E receptors from canine and human liver membranes. The receptors were solubilized with the zwitterionic detergent 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate and were partially purified by DEAE-cellulose chromatography. The apo-B,E(LDL) receptor was isolated by affinity chromatography on LDL-Sepharose. The apo-E receptor, which did not bind to the LDL-Sepharose column, was then purified by using an HDLc (cholesterol-induced high density lipoprotein)-Sepharose affinity column and an immunoaffinity column. Characterization of the receptors revealed that the hepatic apo-B,E(LDL) receptor is similar to the extrahepatic LDL receptor with an apparent Mr = 130,000 on non-reducing sodium dodecyl sulfate-polyacrylamide gels. The apo-E receptor was found to be distinct from the apo-B,E(LDL) receptor, with an apparent Mr = 56,000. The purified apo-E receptor displayed Ca2+-dependent binding to apo-E-containing lipoproteins and did not bind to LDL or chemically modified apo-E HDLc. Antibodies raised against the apo-B,E(LDL) receptor cross-reacted with the apo-E receptor. However, an antibody prepared against the apo-E receptor did not react with the apo-B,E(LDL) receptor. The apo-E receptor also differed from the apo-B,E(LDL) receptor in amino acid composition, indicating that the apo-E receptor and the apo-B,E(LDL) receptor are two distinct proteins. Immunoblot characterization with anti-apo-E receptor immunoglobulin G indicated that the apo-E receptor is present in the hepatic membranes of man, dogs, rats, and mice and is localized to the rat liver parenchymal cells.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001055:Apolipoproteins B / Q000378:metabolism; D001057:Apolipoproteins E / Q000378:metabolism; D001667:Binding, Competitive; D002417:Cattle; D002846:Chromatography, Affinity; D002848:Chromatography, DEAE-Cellulose; D004247:DNA / Q000032:analysis; D004285:Dogs; D006801:Humans; D007163:Immunosorbent Techniques; D008075:Lipoproteins, HDL / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism; D008099:Liver / Q000032:analysis*; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008970:Molecular Weight; D011956:Receptors, Cell Surface / Q000235:genetics / Q000302:isolation & purification*; D011973:Receptors, LDL / Q000032:analysis
D000596:Amino Acids; D001055:Apolipoproteins B; D001057:Apolipoproteins E; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D011956:Receptors, Cell Surface; D011973:Receptors, LDL; D004247:DNA