Transformation and expression of a cloned fimA gene in Porphyromonas gingivalis

The Porphyromonas gingivalis fimbria is an important virulence factor invol ved in the adherence and colonization of the organism in the oral cavity. I n this study, we transformed this organism with a gene, fimA(381), encoding the fimbrial subunit of P. gingivalis 381 (fimbrillin) by using the host-v ector system that we developed previously and examined expression of the cl oned fimA(381) gene. The recombinant plasmid pYRF2 was constructed by ligat ing a fragment containing the fimA(381) gene into the plasmid vector pYH420 and transformed into the restriction-deficient P. gingivalis host YH522. p YHF2 was autonomously maintained in YH522 cells, and the fimbrillin polypep tide (recombinant fimbrillin) was fully expressed. The molecular mass of th e recombinant fimbrillin was evaluated by sodium dodecyl sulfate-polyacryla mide gel electrophoresis as 41 kDa, which was identical to that of the nati ve fimbrillin of strain 381. The amino acid sequences of the 20 amino-termi nal residues of the recombinant fimbrillin and the native fimbrillin of the strain 381 were identical. In addition, characteristic long and thin fimbr ial structures (recombinant fimbriae) that were distinguishable from the ho st's native fimbriae when examined by immunogold electron microscopy were o bserved around the cell surface of the transformants containing the fimA(38 1) gene. These results suggested that transformation of fimA gene from a di fferent strain of P. gingivalis followed by accumulation of the mature fimb rial subunit protein was sufficient for production of fimbrial structures t hat were observable by electron microscopy.