Structure-dependent dynamic binding of tea catechins to mucin: Experimental characterization and multi-ligand...

Tea catechin-mucin interactions are relevant to oral processing and sensory perception, yet their structure-dependent binding behavior remains insufficiently understood. In this study, four representative tea catechins, epicatechin (EC), epicatechin gallate (ECG), epigallocatechin (EGC), and epigallocatechin gallate (EGCG), were compared for their interactions with mucin in aqueous solution using spectroscopy, isothermal titration calorimetry, and multi-ligand molecular dynamics simulations. Dynamic light scattering showed that catechins did not induce pronounced macroscopic precipitation, while ultraviolet and fluorescence spectra revealed detectable changes in the local microenvironment of mucin chromophoric residues. Fluorescence quenching analysis revealed good linear Stern-Volmer relationships, with quenching constants following the order EC > ECG > EGCG > EGC, and the calculated bimolecular quenching rate constants were in the range of 10¹¹-10¹² M^-1 s^-1. Multi-ligand molecular dynamics simulations showed that EGCG exhibited the highest binding probability (about 80%) and the longest average residence time (about 40 ns), followed by ECG (about 70% and 25 ns), whereas EC and EGC remained near 45% binding probability and showed considerably shorter residence times. The averaged binding free energies followed the order ECG ≈ EGCG > EC > EGC. Preliminary sensory evaluation further showed that EGCG and ECG produced higher astringency intensity than EC and EGC, which was broadly consistent with their stronger and more persistent mucin-binding behavior. These results demonstrate that catechin-mucin interactions are strongly structure-dependent and that galloylation promotes stable and persistent multi-point association with mucin.