Analysis of structure and function of saliva protein receptor domains for periodontopathogen

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The objects of this study are to determine the amino acid residues of saliva protein receptors that interact specifically with Porphyromonas gingivalis, and to analyze the function of the receptors. After proline-rich protein (PRP) was proteolysed, the interaction of each PRP fragment with recombinant fimbrillin was examined by ELISA and binding inhibition experiment using ^<125>I-labeled fimbrillin and PRP-coated hydroxyapatite beads (HAP). Analogous peptides corresponding to the fragments which showed the binding activity were synthesized and used to determine the binding domain. Epitope mapping experiments showed that peptide Pro-Gln-Gly-Pro-Pro-Gln was minimal active segment for binding to P.gingivalis fimbriae. Synthetic peptides representing statherin analogs were used to localize the binding domains of statherin. Successive peptides were synthesized by deleting individual amino acid residues from the C and N termini of the peptide that showed the binding activity to fimbrillin. The binding inhibition experiments using the peptides indicated that Leu-29-Tyr-30 and Tyr-41-Thr-42-Phe-43 are important binding regions that mediate the binding of statherin to P.gingivalis. It was shown that fimbriae also bound to proline-rich glycoprotein (PRG) purified from parotid saliva. The peptide analogous to the binding region of PRP significantly inhibited the binding of fimbriae to PRG-coated HAP,while the peptide analogous to the binding region of statherin showed no effect on the fimbrial binding to PRG.The similar result is obtained by Overlay assay. These results suggest that fimbriae bind to saliva through the two distinct binding domains of receptory salivary components, PRG/PRP and statherin.