Objectives: The aim of this study was to investigate the role of an outer membrane protein of Porphyromonas gingivalis (Pg), as a major pathogen in the progression of adult periodontitis. Recently, Omp85, which was conserved among all of Gram negative bacteria, was identified as an essential outer membrane protein for viability in Neisseria meningitidis. We present here some features of Omp85 homologue, PG0191, in Pg. Methods: PG0191 was identified as Omp85 homologue by using BLAST. We predicted the topology of PG0191 according to PROFtmb prediction program. We designed 3 peptides which were suited for loop structure exposed to the outer environment, and synthesized these peptides conjugated to keyhole limpet hemocyanin. Recombinant PG0191(rPG0191) was overexpressed from pGEX6P-PG0191-containing E. coli, and purified by mobility of SDS-PAGE and dialysis. The polyclonal rabbit antibodies against these PG0191 antigens were obtained and used for cross-reactive assay to Pg and antibody-dependent inhibition assay to activities (proliferation, autoaggregation, hemagglutination, and LPS production) of Pg. We also attempted to construct the PG0191-deletion mutant of Pg 381 and ATCC 33277 by allelic replacement. Results: PG0191 presented 25% amino acid homology to neisserial Omp85. Topological prediction of PG0191 indicated that PG0191 was composed of two domains; (1)N-terminal periplasmic domain and (2)C-terminal outer membrane domain with a 14 stranded beta-barrel structure. One of 3 loop peptides or rPG0191 induced the antibodies to rPG0191 or the whole cell of Pg. However, these antibodies did not affect the above activities of Pg. The PG0191-deletion mutant was not obtained, though a null mutation of PG0191 gene was tried by allelic replacement. Conclusion: The construction of rPG0191 was available for induction of antibody to the outer membrane protein of Pg. Our preliminary result suggested that PG0191 might be essential for viability of Pg as well as Omp85 of the other Gram negative bacteria.

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