Purification and partial amino acid sequencing of a fructosyllysine-specific binding protein from cell membranes of the monocyte-like cell line U937.

The ability of short-term in vitro glycated albumin to react with monocytes or the monocyte-like cells U937 is due to the Amadori adduct fructosyllysine. Two binding proteins of about 100 and 200 kDa have been previously described to interact specifically with the monocyte-like cell line U937. Detergent extracts from U937 cell membranes were used to purify the 100kDa protein by ion exchange chromatography, fructosyllysine-Sepharose affinity chromatography and SDS-PAGE. Six amino acids from the N-terminal end and two peptide sequences of 14 and 15 amino acids were identical with the N-terminus and the positions 349 to 362 and 610 to 624 of the major nuclear protein nucleolin. However, ligand blotting experiments with nuclear extracts from U937 and RIN cells showed no binding of glycated albumin with nucleolin. The reported amino acid sequences of the 100kDa fructosyllysine specific binding protein do not show any homologies with AGE-receptors. This receptor protein as a nucleolin-like polypeptide belongs to the superfamily of RNA-binding proteins.