TANNIN INTERACTIONS WITH A FULL-LENGTH HUMAN SALIVARY PROLINE-RICH PROTEIN DISPLAY A STRONGER AFFINITY THAN WITH SINGLE PROLINE-RICH REPEATS

The protein IB5 has been purified from human parotid saliva. This prot ein contains several repeats of a short proline-rich sequence. Dissoci ation constants have been measured at several discrete binding sites u sing H-1-NMR for the hydrolysable tannins (polyphenols) beta-1,3,6-tri -O-galloyI-D-glucopyranose, beta-1,2,4,6-tetra-O-galloyl-D-glucopyrano se and beta-1,2,3,4,6-penta-O-galloyl-D-glucopyranose and the condense d proanthocyanidin (-)-epicatechin. The dissociation constants for tri galloyl glucose and pentagalloyl glucose were 15 X 10(-5) and 1.7 X 10 (-5) M, respectively, which are 115 and 1660 times stronger than those previously measured under the same conditions for a single repeat of a mouse salivary proline-rich protein. The increase in affinity is asc ribed to intramolecular secondary interactions, which are strengthened by the rigidity of the interacting molecules.