Receptor-mediated endocytic uptake of methylglyoxal-modified serum albumin. Competition with advanced glycation end product-modified serum albumin at the advanced glycation end product receptor

Abstract

Methylglyoxal binds and irreversibly modifies arginine and lysine residues in bovine serum albumin (BSA) under physiological conditions, producing a protein with an increased net negative charge at physiological pH. At 4 degrees C, methylglyoxal-modified BSA (MG-BSA) was bound by cell surface receptors on murine P388D1 macrophages. The apparent dissociation constant KD value was 435 +/- 2 nM, and there were 8.89 +/- 0.02 x 10(5) receptors/cell (n = 6), compare with an apparent KD value of 263 +/- 52 nM and 10.17 +/- 0.93 x 10(5) receptors/cell (n = 11) for advanced glycation end product-modified BSA (AGE-BSA). AGE-BSA competed with MG-BSA for binding to a common receptor; however, a component of AGE-BSA receptor binding could not be displaced by MG-BSA, and a component of MG-BSA receptor binding could not be displaced by AGE-BSA, suggesting that there are binding sites for both AGE-BSA and MG-BSA, competitive and noncompetitive, to MG-BSA and AGE-BSA on P388D1 cells at 4 degrees C. At 37 degrees C, receptor binding of AGE-BSA and MG-BSA was followed by endocytosis and lysosomal degradation of the modified protein. Methylglyoxal-modified proteins are ligands for the AGE receptor, and their formation and metabolism may be linked to the development of diabetic complications.