Porphyromonas (Bacteroides) gingivalis fimbrillin: size, amino-terminal sequence, and antigenic heterogeneity

Bacterial fimbriae mediate cell adhesion and are important in colonization. Fimbrial proteins from strains of Porphyromonas (Bacteroides) gingivalis isolated from different individuals were compared for their size, amino-terminal sequence, and antigenic diversity. Two major protein components of the crude fimbrial preparations differed in apparent molecular mass, ranging from 41 to 49 kDa for the fimbrillin monomer and from 61 to 78 kDa for the other major protein. The amino-terminal sequence of the antigenically related group of proteins of the fimbrillin monomer in the 41- to 49-kDa range showed significant homology; however, minor sequence heterogeneity was observed, mainly in residues 4 to 6. One of the observed amino-terminal sequences, AFGVGDDESKVAKLTVMVYNG, resembled the deduced sequence of P. gingivalis 381 (D.P. Dickinson, M. K. Kubiniec, F. Yoshimura, and R.J. Genco, J. Bacteriol. 170:1658-1665, 1988). Fimbriae from all the strains of P. gingivalis showing this sequence contained a fimbrillin monomer of 43 kDa and showed a strong reaction with both polyclonal and monoclonal antibodies directed to the fimbriae from P. gingivalis 2561 (381). Fimbriae from strains showing amino-terminal sequence variations in residues 4 to 6 (i.e., substitution of VGD with either E or NAG) were more diverse in their molecular sizes. Most of these variant fimbriae showed weak reactions with the polyclonal antibodies and no reaction with the monoclonal antibodies induced to the fimbriae of strain 2561. No correlation could be established between the molecular size and immunological reactivity of the fimbrillin monomer of P. gingivalis strains. Strains 9-14K-1 and HG 564 not only showed markedly different sequences from the other three amino-terminal sequences but also did not react with either polyclonal or monoclonal antibodies to the fimbriae of strain 2561. Strains W50, W83, and AJW 5 failed to show any immunological reactivity with the antibodies to fimbrillin or fimbriae of strain 2561. Fimbriae from different strains revealed different immunologic reactions with rabbit antisera to each of the synthetic peptides of residues 59-78 (peptide I), 79-100 (peptide J), and 91-108 (peptide E) of strain 381. These results suggest that P. gingivalis fimbrillin subunits have size, sequence, and antigenic heterogeneity among the strains and that these differences may be important in the function and immune reactivities of the fimbriae.