Identification of linear antigenic sites on the Porphyromonas gingivalis 43-kDa fimbrillin subunit

The fimbrillin of Porphyromonas gingivalis is thought to be an important virulence factor that mediates adherence to host surfaces. The linear immunogenic and antigenic structure of P. gingivalis fimbrillin was investigated with synthetic peptides corresponding to the amino acid sequence predicted from the cloned fimbrillin gene for P. gingivalis 2561. A series of continuous and overlapping peptides corresponding to the entire sequence of P. gingivalis fimbrillin was used to immunize Wistar rats. The resulting polyclonal antibodies were used to test the antigenicity of the 43-kDa fimbrillin protein by enzyme-linked immunosorbent assay and Western blot analysis. All the peptides elicited specific antibodies directed to the corresponding peptides but differed in their ability to elicit antisera that cross-reacted with either native or denatured fimbrillin. Antisera to various C-terminal one-third peptides were more reactive to the denatured monomeric form of fimbrillin by Western blot analysis. Antisera to peptide 99-110 was by far the most reactive against the native form of the oligomeric fimbrillin as well as the partially denatured oligomeric form of fimbrillin. The results indicate that amino acid residues 99-110 on the native fimbrillin protein are accessible to antibody binding and that the immunogen 99-110, when conjugated to thyroglobulin, is able to mimic an epitope on the 43-kDa fimbrillin.