# Unlocking Antioxidant Potential: Interactions Between Cyanidin-3-Glucoside and Corbicula fluminea Protein

## TL;DR

This study explores how the natural antioxidant cyanidin-3-glucoside interacts with Corbicula fluminea protein, revealing both synergistic and antagonistic effects on antioxidant activity.

## Contribution

The paper provides new insights into the interaction mechanism and antioxidant effects of cyanidin-3-glucoside and Corbicula fluminea protein.

## Key findings

- Cyanidin-3-glucoside spontaneously binds to Corbicula fluminea protein, forming a non-covalent complex.
- The interaction alters the protein's conformation and affects its antioxidant capacity in a concentration-dependent manner.
- Lower concentrations of cyanidin-3-glucoside show synergistic effects, while higher concentrations show antagonistic effects.

## Abstract

Oxidative stress is an important inducer of chronic diseases such as cancer and diabetes. Supplementation of exogenous natural antioxidants has become an efficient strategy to alleviate oxidative damage. Polyphenols (e.g., cyanidin-3-O-glucoside and C3G) and aquatic proteins (e.g., Corbicula fluminea protein and CFP) are good candidates. Importantly, these two classes of biomolecules are often combined during food processing, leading to interactions that may significantly alter their properties, particularly their antioxidant capacity. Moreover, the extent of their effects are largely dependent on the strength of the polyphenol–protein affinity, which arises from binding mechanisms and is contingent upon the specific polyphenols/proteins, with some systems exhibiting synergistic effects and others demonstrating antagonistic effects. However, information on the interaction between CFP and C3G remains unclear. In this work, the interaction mechanism underlying the physical mixing of C3G and CFP was analyzed in terms of multi-spectroscopy, thermodynamic analysis, and particle properties. The synergistic antioxidant effect of C3G with CFP was also evaluated. The results show that C3G tended to spontaneously bind to CFP, altered its conformation, and formed a compact non-covalent complex. Although the presence of C3G resulted in enhanced antioxidant capacity, the impact was not significant at high C3G levels. What is more, C3G displayed an antagonistic effect when combined with CFP.

Corbicula fluminea protein (CFP) and cyanidin-3-O-glucoside (C3G) are natural nutrient fortifiers. During consumption or processing, they may interact with each other, inducing alternations in their structural and functional properties. However, nothing was known about the mechanism of their interaction and their synergistic antioxidant effect. In this research, C3G was physically mixed with CFP to simulate practical scenarios. The impact of the presence of C3G on the multispectral characteristics, antioxidant activity, and particle properties of CFP was examined and compared to chemically fabricated C3G-CFP covalent conjugates. The results indicate that C3G tended to spontaneously bind to CFP and formed compact non-covalent complex, with hydrophobic forces predominantly governing the interaction. This binding resulted in the statically quenched intrinsic fluorescence of CFP, accompanied by a dynamic model. Moreover, C3G preferentially induced Trp residue in CFP exposed to a more polar microenvironment, yet it exerted nearly no effects on CFP when analyzed using ultraviolet–visible (UV-Vis) spectroscopy and synchronous fluorescence spectroscopy (SFS). Additionally, although the formed non-covalent complex demonstrated strengthened antioxidant capacity, C3G displayed an antagonistic effect with CFP, whereas lower C3G concentrations led to synergistic effects in covalent conjugates. These findings provide new insights into the effective application of C3G and CFP as nutritional antioxidants.