Mechanism evaluation of the interactions between eight flavonoids and γ-globulin based on multi-spectroscopy

Abstract

The binding of eight classic flavonoids (including baicalin, quercetin, myricetin, rutin, puerarin, daidzein, hesperidin and isoliquiritin) to γ-globulin was investigated by steady state and time-resolved fluorescence, UV–vis absorption spectroscopy and circular dichroism (CD) spectroscopy. Fluorescence data reveal that the fluorescence quenching mechanisms of γ-globulin by flavonoids are all static quenching procedure. The binding affinity is strongest for baicalin and ranks in the order baicalin>myricetin>isoliquiritin>rutin>daidzein>quercetin>hesperidin>puerarin. The thermodynamic analysis implies that electrostatic forces, hydrogen bonding and/or hydrophobic interactions are the main interactions. Synchronous fluorescence spectroscopy shows the interaction between flavonoids and γ-globulin chang the hydrophobicity of the microenvironment of tryptophan (Trp) residues. All flavonoids close to tyrosine (Tyr) residues but have no effect on the microenvironment around Tyr-residues except for γ-globulin-hesperidin/isoliquiritin system. UV–vis absorption spectroscopy explains that the interaction between flavonoids and γ-globulin leads to the loosening and unfolding of the protein backbone. Furthermore, the CD data demonstrate that conformational change at the secondary structural level of γ-globulin is altered in the presence of flavonoids. We anticipate that this study can provide better knowledge of bioavailability such as absorption, biodistribution, and elimination of flavonoids in vivo, to facilitate the comprehension of the biological responses to physiologically relevant flavonoids.