Molecular interactions of food additive dye quinoline yellow (Qy) with alpha-lactalbumin: Spectroscopic and computational studies

Food dye quinoline yellow(Qy) induced conformational change in bovine alpha-lactalbumin (alpha LA), and its interaction mechanism was investigated at physiological pH. We used several biophysical techniques (circular dichroism (CD), intrinsic fluorescence, UV-Vis absorption), and computational techniques (molecular docking and simulation). Our intrinsic fluorescence results suggested that Qy dye quenched the intrinsic fluorescence of alpha LA via a dynamic quenching mechanism because the quenching constant increased with elevation in temperature. We also found that aLA had one equivalent binding site for Qy dye, and that the affinity of Qy dye towards alpha LA was of the order of 105 mol/L. Thermodynamic analysis of alpha LA-Qy dye interactions revealed the spontaneous nature of such interactions. The positive values of enthalpy and entropy change explained that the interactions between Qy dye and alpha LA were driven mainly by hydrophobic interactions. The far-UV CD and UV-absorption results revealed that the alpha LA conformation changes because of Qy dye interactions. Molecular docking results indicated that Qy dye binds strongly at a major binding site of alpha LA and that alpha LA-Qy dye complex is stabilized by hydrogen bonding, salt bridge, Pi-cation, and van der Waals interaction. The molecular dynamics simulation study of alpha LA-Qy complexes revealed the formation of a stable interaction between them. This study can provide new insights into a comprehensive understanding of food dye-induced conformational changes in biological processes. (C) 2020 Elsevier B.V. All rights reserved.