Probing the binding sites of resveratrol, genistein, and curcumin with milk β-lactoglobulin.

We determined the binding sites of curcumin (cur), resveratrol (res), and genistein (gen) with milk β-lactoglobulin (β-LG) at physiological conditions. Fourier transform infrared spectroscopy, circular dichroism, and fluorescence spectroscopic methods as well as molecular modeling were used to determine the binding of polyphenol-protein complexes. Structural analysis showed that polyphenols bind β-LG via both hydrophilic and hydrophobic contacts with overall binding constants of Kcurcumin-β-LG = 4.4 (± .4) × 10⁴ M⁻¹, Kresveratrol-β-LG = 4.2 (± .2) × 10⁴ M⁻¹, and Kgenistein-β-LG = 1.2 (± .2) × 10⁴ M⁻¹. The number of polyphenol molecules bound per protein (n) was 1 (cur), 1.1 (res), and 1 (gen). Molecular modeling showed the participation of several amino acid residues in polyphenol-protein complexation with the free binding energy of -12.67 (curcumin-β-LG), -12.60 (resveratrol-β-LG), and -10.68 kcal/mol (genistein-β-LG). The order of binding was cur > res > gen. Alteration of the protein conformation was observed in the presence of polyphenol with a major reduction of β-sheet and an increase in turn structure, causing a partial protein structural destabilization. β-LG might act as a carrier to transport polyphenol in vitro.