Multi-spectroscopic Analysis of the Interaction and Molecular Docking Between Cyanidin-3-glucoside and Soy Protein

The interaction mechanism of cyanidin-3-glucoside (C3G) with β-conglycinin and glycinin was investigated by multiple spectroscopies and molecular docking. The results showed that C3G quenched the intrinsic fluorescence of β-conglycinin/glycinin strongly in both static and dynamic modes and C3G had stronger binding affinity toward glycinin than β-conglycinin. However, the major interaction force involved in C3G binding to glycinin was different from that for β-conglycinin. As judged from the number of binding sites, a stable C3G-soy protein complex with a molar ratio of 1:1 was formed. C3G induced partial unfolding of the secondary structure of soy protein and a conformational switch from α-helix to β-sheet, thus resulting in conformational unfolding of soy protein. The addition of C3G could reduce the hydrophobicity of the microenvironment around tryptophan residues in β-conglycinin, but had no significant effect on the microenvironment around amino acid residues in glycinin. In addition, the majority of the phenolic hydroxyl groups in the C3G molecule were mainly involved in hydrogen bonds and hydrophobic interaction with soy protein. Compared with β-conglycinin, glycinin showed great potential as a biological carrier for the stabilization and delivery of C3G. However, it may be unfavorable for the biological activity of C3G.