Molecular mechanism of epicatechin gallate binding with carboxymethyl β-glucan and its effect on antibacterial activity

The non-covalent binding between flavanols and polysaccharides has impacts on their bioactivities, but the binding mechanism is less understood. This work aimed to unveil the non-covalent interactions between epicatechin gallate (ECG) and anionic carboxymethyl Poria cocos polysaccharide (CMPN) at the structural and molecular level based on the synergistic antibacterial effect between them. The results suggested that there was hydrogen bonding, hydrophobic and electrostatic interaction between ECG and CMPN, which was also supported by the results of molecular dynamics simulations. The resulting changes in physicochemical properties enhanced the antibacterial activity of the ECG-CMPN mixture. More specifically, through two-dimensional Fourier transform infrared correlation spectrum (2D-FT-IR) and nuclear magnetic resonance spectroscopy (NMR) analysis, COO- in CMPN carboxymethyl and CO in ECG galloyl had the highest response priority and binding strength in the interaction, allowing us to conclude the critical functional groups that affect the non-covalent interactions of polysaccharide and flavanols and their bioactivities.