PORPHYROMONAS-GINGIVALIS FIMBRIAE MEDIATE COAGGREGATION WITH STREPTOCOCCUS-ORALIS THROUGH SPECIFIC DOMAINS

Fimbriae are major adhesive components on the cell surface of Porphyro monas gingivalis. In this study, we evaluated the role of fimbriae in coaggregation with Streptococcus oralis. Fimbriae purified from P. gin givalis competitively inhibited the coaggregation by 100% at a concent ration of 50 mu g/mL. On the other hand, the same amount of lipopolysa ccharide isolated from P. gingivalis was inhibited by only 25% of the level of the fimbriae. A fimA-inactivated mutant of P. gingivalis fail ed to show distinct coaggregation activity. Fimbriae added to a soluti on of various strains of streptococci caused their self-aggregation at a concentration of 10 to 30 mu g/mL. The self-aggregation induced by fimbriae was inhibited by lambda-arginine (20 to 40 mM/L). Iodinated f imbriae reacted with S. oralis cells immobilized on the nitrocellulose membrane, and 100 degrees C heating of the cells diminished the bindi ng abilities. Recombinant fimbrillin (r-Fim, corresponding to whole re sidues 1 to 337 of native fimbrillin) of P. gingivalis also showed 100 % inhibition of the coaggregation. The r-Fim variant (residues 1 to 28 6) lacking the C-terminal 51 residues was as inhibitory as r-Fim. Howe ver, the variant (residues 1 to 265) without the C-terminal 72 residue s lost 77% of the inhibitory activity. These findings suggested that r esidues 266 to 286 contain a domain involved in the coaggregation of P . gingivalis with S. oralis. Inhibition by three polypeptides correspo nding to residues 266 to 286, 266 to 337, and 287 to 337 was studied. Peptides 266 to 286 and 266 to 337 inhibited by 96 and 100%, respectiv ely, at a concentration of 1.5 nmol/mL. Peptide 287 to 337 also showed a significant inhibitory effect but to a slightly lesser extent than that of peptide 266 to 286. P. gingivalis fimbriae appear to be involv ed in coaggregation with streptococci, probably through an adhesive pr otein molecule(s) of the latter, and the fimbriae possess several doma ins in the C-terminal residues 266 to 337 for interaction with S. oral is.