High density lipoprotein binding protein of eel (Anguilla japonica) liver with specificity of binding to apoAI as a ligand

High-density lipoprotein (HDL) binding protein (HBP) was isolated from the microsomal fraction of eel liver homogenate by affinity chromatography with a HDL-column. After SDS-PAGE and blotting, IIBP on the PVDF membrane was d etected by FITC-labeled HDL and apolipoprotein AI (apoAI) as a ligand. HBP in the microsomal fraction was most abundant among microsomal, mitochondria l and cytosolic fractions. The IIBP isolated by a HDL-column consisted of a t least three proteins with low molecular weights of 18.5, 14.5 and 13.5 kD a; the main component was 14.5 kDa. These proteins are not products of prot ease digestion, as the procedure was carried out in the presence of proteas e inhibitors including (p-aminophenyl) methansulfonyl fluoride, 4-(2-aminoe thyl)-benzenesulfonyl fluoride, pepstatin A, E-64, bestatin, leupeptin, apr otinin and EDTA. The HBP specifically bound to FITC-apoAI and faintly bound or did not bind to FITC-apoAII. Furthermore, binding of HDL labeled with l ipophilic fluorescence to isolated eel hepatocytes was inhibited by the ant ibody to apoAI, but not inhibited by the antibody to apolipoprotein AII (ap oAII). These results strongly suggest that the HBP isolated from the micros omal fraction is present on the plasma membrane of eel liver and plays impo rtant roles for the lipid transport through the interaction with HDL. (C) 2 001 Elsevier Science Inc. All rights reserved.