Characterization of a solubilized cell surface binding protein on macrophages specific for proteins modified nonenzymatically by advanced glycosylated end products.

Glucose can react nonenzymatically with free protein amino groups to form Amadori products, 1-amino-1-deoxyketose residues. These adducts can undergo subsequent rearrangements and dehydrations to form a complex group of brown, fluorescent pigments collectively referred to as advanced glycosylation end products (AGE). One AGE has been identified as 2-(2-furoyl)-4(5)-(2-furanyl)-1H-imidazole (FFI). The AGE-protein adducts accumulate with time and are implicated in irreversible tissue damage. We have previously demonstrated that macrophages bind and degrade AGE-proteins via a specific cell surface binding protein, thus selectively removing senescent macromolecules. In the present communication, we have solubilized this binding protein from the membranes of the murine macrophage cell line RAW 264.7. We have characterized the nature of binding protein-ligand interaction by competition studies using modified ligands. The data indicate that the carbonyl group, the furan ring(s), and the central imidazole structure are all important in the binding protein-ligand interaction. We have established that the binding constant (Ka) of binding protein for the ligand FFI-BA is 3.1 X 10(7) M-1. Chemical crosslinking studies have demonstrated that the molecular weight of the binding protein is 90,000.