Modification of bovine beta-lactoglobulin by glycation in a powdered state or in an aqueous solution: effect on association behavior and protein conformation.

The effect of glycation with lactose on the association behavior and conformational state of bovine beta-lactoglobulin (beta-LG) was studied, using size exclusion chromatography, polyacrylamide gel electrophoresis, proteolytic susceptibility, and binding of a fluorescent probe. Two modification treatments were used, i.e., aqueous solution glycation and dry-way glycation. The results showed that the latter treatment did not significantly alter the nativelike behavior of the protein while the former treatment led to important structural changes. These changes resulted in a specific denatured beta-LG monomer, which covalently associated via the free thiol group. The homodimers thus formed and the expanded monomers underwent subsequent aggregation into a high molecular weight species, via noncovalent interactions. The association behavior of glycated beta-LG is discussed with respect to the known multistep denaturation/aggregation process of nonmodified beta-LG.