Identification of Porphyromonas gingivalis prefimbrilin possessing a long leader peptide: possible involvement of trypsin-like protease in fimbrilin maturation.

Fimbriae of Porphyromonas gingivalis have been shown to be important as one of the virulence factors for colonization on mucosal surfaces. The gene (fimA) encoding the fimbrial subunit (fimbrilin) was overexpressed in Escherichia coli by using a bacteriophage T7 promoter-polymerase expression vector system. Analysis of the resulting fimA gene product revealed that the prefimbrilin had a 46 amino acid leader peptide. This extremely long leader peptide was cleaved from the prefimbrilin by treatment with trypsin or P. gingivalis extracts containing trypsin-like protease activity, resulting in production of a mature fimbrilin. We also found that some transposon-induced trypsin-like protease deficient mutants of P. gingivalis exhibited deficiency in fimbriation and that one of the mutants accumulated a fimbrilin precursor possessing a 25 amino acid leader peptide in the cell. The presence of an extremely long leader peptide and the requirement for a leader peptidase with a substrate specificity similar to that of P. gingivalis trypsin-like protease for fimbrilin maturation indicate that P. gingivalis fimbrilin is a novel type that is different from fimbrilins of type I and IV families.