BINDING OF PORPHYROMONAS-GINGIVALIS FIMBRIAE TO PROLINE-RICH GLYCOPROTEINS IN PAROTID-SALIVA VIA A DOMAIN SHARED BY MAJOR SALIVARY COMPONENTS

Porphyromonas gingivalis, a putative periodontopathogen, can bind to h uman saliva through its fimbriae. We previously found that salivary co mponents from the submandibular and sublingual glands bind to P. gingi valis fimbriae and that acidic proline-rich protein (PRP) and statheri n function as receptor molecules for fimbriae. In this study, we inves tigated the fimbria-binding components in parotid saliva. Fractionated human parotid saliva by gel-filtration chromatography was immobilized onto nitrocellulose membranes for the overlay assay following sodium dodecyl sulfate-polyacrylamide gel electrophoresis, The salivary compo nents on the membrane were allowed to interact with fimbriae purified from P. gingivalis ATCC 33277, and the interacted fimbriae mere probed with anti-fimbria antibodies, The fimbriae were shown to bind to two forms of proline-rich glycoproteins (PRGs) as well as to acidic PRPs a nd statherin, Moreover, fimbriae bound to several components of smalle r molecular size which appeared to be acidic PRP variants and basic PR Ps, Fimbriae bound strongly to the purified PRGs adsorbed onto hydroxy apatite (HAP) beads. In contrast, PRGs in solution failed to inhibit t he fimbrial binding to the immobilized PRGs on the HAP beads. These fi ndings suggest that the appearance of binding site(s) of PRGs can be a scribed to their conformational changes, We previously identified the distinct segments within PRP and statherin molecules that are involved in fimbrial binding, The peptides analogous to the binding regions of PRP and statherin (i.e., PRP-C and STN-C) markedly inhibit the bindin g of fimbriae to PRP and statherin immobilized on the HAP beads, respe ctively. The PRP-C significantly inhibited the binding of fimbriae to PRG-coated HAP beads as well as to PRP on HAP beads, The peptide did n ot affect the binding of fimbriae to statherin, whereas the STN-C show ed no effect on the fimbrial binding to PRPs or PRGs, In the overlay a ssay, the PRP-C clearly diminished the interactions between the fimbri ae and the various salivary components, including PRPs, the PRGs, and the components with smaller molecular sizes brat not statherin, These results strongly suggest that fimbriae bind to salivary components (ex cept statherin) via common peptide segments. It is also suggested that fimbriae bind to saliva through the two distinct binding domains of r eceptory salivary components: (i) PRGs and PRPs and (ii) statherin.