Interaction between glycated serum albumin and AGE-receptors depends on structural changes and the glycation reagent

Physiologically relevant reactive carbonyl compounds vary greatly in their glycation reactivity and the resulting advanced glycation endproducts (AGE) are likely to have distinct structural and biological properties. We characterized a panel of twenty AGE-BSA preparations in terms of (i) their biophysical properties, (ii) their binding to the receptor for advanced glycation endproducts (RAGE) and galectin-3, and (iii) their effects on cellular proliferation. We could establish correlations between lysine glycation and changes in secondary structure. Circular dichroism and differential scanning calorimetry experiments showed that glycation causes albumin to adopt folding properties of a molten globule. Binding studies between AGE-albumin and RAGE or galectin-3 indicate that binding to the isolated receptor domains was weak. Only AGE compounds derived by glycation with ribose were able to bind tightly (K(d) < 10 μM) to both AGE receptors. Cell based assays using an engineered melanoma cell line demonstrated correlations between the extent of (i) lysine side chain modification, (ii) β-sheet content and (iii) albumin multimerization with stimulation of cell proliferation. However, in addition to structural properties of the protein, the chemical structures of the AGE-modifications were important for receptor binding and biological activity as well.