Comparison of binding interactions of cyanidin-3-O-glucoside to β-conglycinin and glycinin using multi-spectroscopic and thermodynamic methods.

Abstract This work aims to explore the molecular binding mechanisms of two major soy protein fractions, β-conglycinin (7S) and glycinin (11S) with cyanidin-3-O-glucoside (C3G, a representative polyphenol in food) at pH 7.0. Circular dichroism spectroscopy manifested that C3G induced the conversion of β-sheet into α-helix and random coil. Synchronous fluorescence and three-dimensional fluorescence spectroscopy confirmed the unfolding and loosing of protein molecules. Furthermore, the results from fluorescence quenching and isothermal titration calorimetry indicated that C3G quenched fluorescence of two proteins in a static mode, and their interactions were entropically favorable processes driven by a combination of hydrophobic interaction and electrostatic force. 11S had a higher affinity for C3G than 7S, as indicated by the binding constant and binding sites. In addition, the surface hydrophobicity and thermal stability of two proteins were reduced after C3G binding. This study will help further understand the interaction mechanism between 7S/11S and polyphenols. Graphical abstract Image 1 Highlights • The binding interactions between 7S/11S and C3G at neutral pH were investigated for the first time. • Their interactions were entropically favorable processes driven by electrostatic and hydrophobic interaction. • Their interactions changed the secondary and tertiary structure of two proteins. • Their interactions decreased the surface hydrophobicity and thermal stability of two proteins. • 11S had a stronger binding ability and more binding sites for C3G than 7S. [ABSTRACT FROM AUTHOR]