Abstract: In order to improve the poor water solubility of quercetin, the mechanism of quercetin binding to β-lactoglobulin B was studied by various spectroscopies, isothermal titration calorimetry and molecular simulation, and changes in the secondary structure of β-lactoglobulin B and quercetin solubility were determined after the binding reaction. The results showed that quercetin was able to bind to β-lactoglobulin B through hydrogen bonding and van der Waals forces. Threedimensional fluorescence spectra, synchronous fluorescence spectra and UV-visible absorption spectra demonstrated that quercetin quenched β-lactoglobulin B fluorescence strongly in the static mode. Furthermore, circular dichroism and Fourier transform infrared spectra indicated that quercetin induced partial transition of α-helix to β-structures in β-lactoglobulin B. Moreover, molecular simulation results showed that the binding site of quercetin on β-lactoglobulin B was located in a cavity formed by α-helix and β-turn, and 8 amino acid residues were involved in the binding site. In combination with quercetin, the threonine residue at position 125 provided strong hydrogen bonds, while the remaining residues provided van der Waals forces. Besides, the solubility of quercetin was increased by about 1 844 times after its conjugation to β-lactoglobulin B. In summary, the water solubility of quercetin can be significantly improved by conjugating it to β-lactoglobulin B.

Key words: quercetin, β-lactoglobulin B, binding mechanism, secondary structure change, solubility