Posttranslational modifications of the insulin-like growth factor-binding protein 3 in patients with type 2 diabetes mellitus assessed by affinity chromatography

Structural and ligand-binding properties of the insulin-like growth factor-binding protein (IGFBP)-3 in patients with poorly controlled diabetes mellitus type 2 were investigated using boronic acid- and lectin-affinity chromatography. IGFBP-3 species separated by chromatography were analyzed by immunoblotting and surface-enhanced laser desorption/ionization-time of flight mass spectrometry (SELDI-TOF MS). Increased IGFBP-3 binding to boronic acid in patients was shown to be accompanied by the increased ligand-binding. Increased binding of IGFBP-3 forms to lectins from Sambucus nigra (SNA) and Canavalia ensiformis (ConA) in patients, on the other hand, was either not accompanied by altered ligand-binding (in the case of ConA) or it was reduced (in the case of SNA). Strong and opposite effects of glycation and additional sialylation on ligand binding qualify them as factors that may be involved in the regulation of the amount of free, physiologically active IGFs, and modulation of processes that accompany development and progression of diabetes. SELDI-TOF MS analysis revealed a fragment of 13.9 kDa as representative for the non-glycosylated form of IGFBP-3, whereas a fragment of 28.0 kDa profiled as typical for the glycosylated/glycated IGFBP-3 species. The same fragmentation pattern found in healthy persons and in patients indicates that the same degradation process predominantly occurs in both groups of individuals.