Salivary receptors for recombinant fimbrillin of Porphyromonas gingivalis

Fimbriae are considered important in the adherence and colonization of Porphyromonas gingivalis in the oral cavity. It has been demonstrated that purified fimbriae bind to whole human saliva adsorbed to hydroxyapatite (HAP) beads, and the binding appears to be mediated by specific protein-protein interactions. Recently, we expressed the recombinant fimbrillin protein (r- Fim) of P. gingivalis corresponding to amino acid residues 10 to 337 of the native fimbrillin (A. Sharma, H. T. Sojar, J.-Y. Lee, and R. J. Genco, Infect. Immun. 61:3570-3573, 1993). We examined the ability of individual salivary components to promote the direct attachment of r-Fim to HAP beads. Purified r-Fim was radiolabeled with ¹²⁵I and incubated with HAP beads which were coated with saliva or purified individual salivary components. Whole, parotid, and submandibular-sublingual salivas increased the binding of ¹²⁵I-r-Fim to HAP beads. Submandibular-sublingual saliva was most effective in increasing the binding of ¹²⁵I-r-Fim to HAP beads (1.8 times greater than that to uncoated HAP beads). The binding of ¹²⁵I-r-Fim to HAP beads coated with acidic proline-rich protein 1 (PRP1) or statherin was four and two times greater, respectively, than that to uncoated HAP beads. PRP1 and statherin molecules were also found to bind ¹²⁵I-r-Fim in an overlay assay. The binding of intact P. gingivalis cells to HAP beads coated with PRP1 or statherin was also enhanced, by 5.4 and 4.3 times, respectively, over that to uncoated HAP beads. The interactions of PRP1 and statherin with ¹²⁵I-r-Fim were not inhibited by the addition of carbohydrates or amino acids. PRP1 and statherin in solution did not show inhibitory activity on ¹²⁵I-r-Fim binding to HAP beads coated with PRP1 or statherin. These results suggest that P. gingivalis fimbriae bind strongly through protein- protein interactions to acidic proline-rich protein and statherin molecules which coat surfaces.