Apolipoprotein E-binding proteins isolated from dog and human liver

Arteriosclerosis. May-Jun 1988;8(3):288-97. doi: 10.1161/01.atv.8.3.288.

Abstract

Chylomicron remnant catabolism appears to be mediated by apolipoprotein (apo) E binding to hepatic lipoprotein receptors. Previously, the apo B,E(LDL) receptor and a unique apo E-binding protein (referred to as the apo E receptor) were isolated from solubilized canine and human livers. In the present study, the apo E-binding fraction was further characterized and found to contain at least three proteins, all of which bind apo E-containing lipoproteins with high affinity. The 56-kDa band was found to contain the alpha- and beta-subunits of F1-ATPase, presumably derived from mitochondrial membranes. In addition, an apo E-binding protein with an apparent Mr approximately equal to 59,000 was identified. The 59-kDa protein displays calcium-independent binding on ligand blots, but displays both calcium-dependent and -independent binding in assays performed with detergent-solubilized protein. The 59-kDa protein recognized lipid-free as well as lipid-bound apo E in ligand blots, and also bound apo E-2, apo E-3, and apo E-4 in a comparable way. Monoclonal antibodies produced against the 59-kDa protein did not react with the 56-kDa proteins. Normal human liver, as well as the liver of a patient lacking the apo B,E(LDL) receptor, possessed the 56-kDa and 59-kDa proteins. These data indicate that liver cells possess at least three proteins, in addition to the apo B,E(LDL) receptor, that bind apo E-containing lipoproteins with high affinity. The physiological role of these proteins in apo E metabolism remains to be determined.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Apolipoproteins E / metabolism*
  • Chromatography, Affinity
  • Chromatography, Agarose
  • Chromatography, DEAE-Cellulose
  • Chylomicrons / metabolism
  • Dogs
  • Electrophoresis, Polyacrylamide Gel
  • Humans
  • Immunoassay
  • Liver / metabolism*
  • Low Density Lipoprotein Receptor-Related Protein-1
  • Membrane Proteins / analysis
  • Membrane Proteins / isolation & purification
  • Molecular Weight
  • Protein Binding
  • Receptors, Cell Surface / analysis
  • Receptors, Cell Surface / isolation & purification*
  • Solubility

Substances

  • Apolipoproteins E
  • Chylomicrons
  • Low Density Lipoprotein Receptor-Related Protein-1
  • Membrane Proteins
  • Receptors, Cell Surface