Purification and characterization of a novel secondary fimbrial protein from Porphyromonas gingivalis strain 381

We previously reported the existence of two different kinds of fimbriae expressed by Porphyromonas gingivalis ATCC 33277. In this study, we isolated and characterized a secondary fimbrial protein from strain FPG41, a fimA-inactivated mutant of P. gingivalis 381. FPG41 was constructed by a homologous recombination technique using a mobilizable suicide vector, and failed to express the long fimbriae (41-kDa fimbriae) that were produced on the cell surface of P. gingivalis 381. However, short fimbrial structures were observed on the cell surface of FPG41 by electron microscopy. The fimbrial protein was purified from FPG41 by DEAE-Sepharose CL-6B column chromatography. The secondary fimbrial protein was eluted at 0.15 M NaCl, and the molecular mass of this protein was approximately 53 kDa as estimated by SDS-PAGE. An antibody against the 53-kDa fimbrial protein reacted with the short fimbriae of the FPG41 and the wild-type strain. However, the 41-kDa long fimbriae of the wild-type strain and the 67-kDa fimbriae of ATCC 33277 did not react with the same antibody. Moreover, the N-terminal amino acid sequence of the 53-kDa fimbrial protein showed only 2 of 15 residues that were identical to those of the 41-kDa fimbrial protein. These results show that the properties of the 53-kDa fimbriae are different from those of the 67-kDa fimbriae of ATCC 33277 as well as those of the 41-kDa fimbriae.