The Ability of Basic and Glycosylated Proline-Rich Proteins to Protect Oral Enzymes from Polyphenol Inhibition

Tannins and flavan-3-ols can exhibit astringency and potential antinutritional effects by binding, aggregating, and precipitating proteins, including digestive and oral enzymes. During oral food processing, these polyphenolic compounds may inhibit enzymes, such as β-glucosidase and glutathione transferase (GSTP1), which help generate taste-active molecules or transform food components for elimination. Saliva contains proline-rich proteins (PRPs) with high affinity for tannins and flavan-3-ols, potentially protecting oral enzymes from inhibition. This study investigates the ability of two PRP classes─basic (bPRPs) and glycosylated (gPRPs)─to protect β-glucosidase and GSTP1 from polyphenols such as tannins and flavan-3-ols. Recombinant PRPs were produced, purified, and tested for their protective effects on the enzyme activity in the presence of epigallocatechin gallate (EGCG) and tannic acid. Limited protection by bPRP was observed for GSTP1, notably at a PRP-to-polyphenol ratio of 5:1 with either EGCG or tannic acid and at 10:1 only with tannic acid. In contrast, gPRP significantly protected both β-glucosidase and GSTP1 under various conditions involving EGCG and tannic acid.