Understanding molecular interaction between thermally modified β-lactoglobulin and curcumin by multi-spectroscopic techniques and molecular dynamics simulation

This study elucidated the binding of curcumin (CUR) onto preliminary thermally modified beta-lactoglobulin (beta-LG). beta-LG at pH 8.1 was heated at 75 degrees C, 80 degrees C and 85 degrees C for 10 min to construct denatured proteins (beta-LG75, ss-LG80, beta-LG85). Steady and time-resolved fluorescence studies uncovered that CUR quenched proteins in simultaneous static and dynamic mode. Pre-heating beta-LG improved its binding with CUR and the strongest affinity occurred in beta-LG80. Fluorescence resonance energy transfer (FRET) analysis indicated that binding distance between CUR and beta-LG80 was the smallest and energy transfer was the most efficient. beta-LG80 had the highest surface hydrophobicity. Fourier-transform infrared (FT-IR) spectroscopy and differential scanning calorimeter (DSC) confirmed that CUR transferred from crystal to amorphous state after association with protein and revealed the contribution of hydrogen bonds. Combination of beta-LG80 with CUR retained the antioxidant capacity of each component. Molecular dynamics simulation demonstrated enhanced hydrophobic solvent accessible surface area of beta-LG80 compared with native protein. Data obtained from this study may provide useful information for comprehensively understanding the ability of beta-lactoglobulin to bind hydrophobic substances under different environmental conditions like high temperature and alkaline medium.