Deciphering Polyphenol Interactions with Poly(L-proline) and Polysarcosine.

Natural polyphenols extensively interact with proteins, with proline-rich proteins (PRPs) identified as their primary binding partners. While the structural rigidity of proline is widely considered as the main driver of these interactions, its exact molecular role remains poorly understood. In this study, we utilize poly(L-proline) (PLP) and polysarcosine (PSar) as structurally related but conformationally distinct minimalist models to delineate these interactions. Surprisingly, both the rigid PLP and the highly flexible PSar exhibit strong, micromolar-level binding affinities with polyphenols. Isothermal titration calorimetry (ITC) and molecular dynamics (MD) simulations reveal that their binding modes have different thermodynamic profiles dictated by backbone flexibility. For the rigid PLP, binding is synergistically driven by enthalpy and entropy; hydrogen bonds provide enthalpic stabilization, while solvent displacement yields entropic gains. In contrast, the flexible PSar backbone introduces a conformational entropy penalty upon binding. Leveraging this unexpected high-affinity interaction, a hydrogel with the noncovalent/covalent network using EGCG and star-shaped PSar polymers was fabricated, exhibiting unique macroscopic assembly and sustained release capabilities. In conclusion, our study provides a unified thermodynamic framework for understanding the interactions between natural polyphenols and polypept(o)ides.