Impact of Proline-Rich Salivary Proteins on Interactions between Catechin and Polysaccharides.

The modulation of interactions between catechin and two structurally distinct wine polysaccharides (mannan and pectin) by proline-rich salivary proteins (PRPs) was investigated using saturation transfer difference nuclear magnetic resonance (STD NMR). Mannan-catechin interactions, driven by CH-π stacking and hydrophobic effects, were weakened by both acidic and basic PRPs. This competitive interference increased the apparent dissociation constant (KD) from ≈231 μM to ≈272 and 279 μM, respectively. Conversely, catechin-pectin binding (baseline KD ≈ 230 μM) was unaffected by acidic PRPs but synergistically enhanced by basic PRPs (KD ≈ 195 μM) due to favorable electrostatic attractions. Epitope mapping confirmed that catechin binds differently depending on the polysaccharide structure. Ultimately, the results reveal a dual regulatory pattern: PRPs act as competitive antagonists for neutral polysaccharides (mannan) and cooperative synergists for charged ones (pectin). These molecular insights provide a concrete biophysical basis for strategically managing wine astringency and sensory quality.