Role of the carboxyl-terminal region of Porphyromonas gingivalis fimbrillin in binding to salivary proteins.

Porphyromonas gingivalis fimbriae are considered to play an important role in the adherence and colonization of the bacteria in the oral cavity. In this study, we generated and purified three carboxyl-terminal variants of recombinant fimbrillin (r-FimA 224-337, r-FimA 266-337, and r-FimA 287-337, corresponding to amino acid residues 224 to 337, 266 to 337, and 287 to 337, respectively, of the 43-kDa fimbrillin of P. gingivalis 2561). They were used as inhibitors of P. gingivalis cell binding to human salivary protein-coated hydroxyapatite (HAP) beads. All of the carboxyl-terminal region polypeptides inhibited binding in a dose-dependent manner; however, the inhibitory effect of r-FimA 287-337 was less than that of the other two polypeptides when HAP beads were coated with whole saliva or purified salivary proline-rich protein 1 (PRP1). Assays of binding of a synthetic peptide corresponding to amino acid residues 266 to 286 of P. gingivalis 2561 fimbrillin to salivary proteins showed that this peptide bound strongly to whole saliva or PRP1 but only weakly to statherin. These results suggest that the carboxyl-terminal region corresponding to amino acid residues 266 to 337 of P. gingivalis fimbrillin plays an important role in binding to salivary proteins and that the domain corresponding to amino acids 266 to 286 is likely a major binding site for PRP1s and the domain corresponding to amino acids 287 to 337 is likely a major binding site for statherin.