Albumin conformational changes during glycation and thermal denaturation processes revealed by fluorescence spectroscopy and small-angle X-ray scattering

Background and Objectives: Objects of the research in this study are solutions of bovine serum albumin (BSA) and its aggregates. Structural changes of the protein molecules in solution with pH 3 and pH 7.4 are investigated during glycation and thermal denaturation processes, when the BSA molecules in solution undergo similar intermediate states. The main aim of the research is to compare structural changes of the BSA upon its glycation and thermal denaturation, revealed by combination of optical and X-ray techniques. Materials and Methods: The main techniques used in this study were steady-state and time-resolved fluorescence spectroscopy, as well as small angle X-ray scattering (SAXS). Results: Position of maximum in tryptophan fluorescence spectrum and tryptophan fluorescence lifetime are sensitive to BSA conformational changes at pH 7.4 upon its incubation at 65$^{\circ}$C. Availability of hydrophobic binding sites of NR significantly increases upon glycation. No alterations of these photophysical parameters are observed at pH 3. However, SAXS experiments reveal presence of BSA aggregates at 25$^{\circ}$C and above. Further incubation of the solution at 65$^{\circ}$ C is not accompanied by changes in the local environment of tryptophan residues or appearance/accessibility enhancement of hydrophobic sites in the protein structure. Conclusion: This study shows that structural changes of the BSA molecules differ for glycated and thermally denatured / aggregated proteins, though the molecules undergo similar intermediate states during these processes.