The anaerobic oral bacterium
Porphyromonas gingivalis is thought to be a major etiologic agent of progressive periodontal disease. Recently, two major cysteine proteinases responsible for trypsine-like activity from the organism were purified from the culture supernatant of various
P. gingivalis strains, termed “Arg-gingipain (RGP) and Lys-gingipain (KGP) ”. The secretory RGP and KGP were shown to be associated with periodontal tissue breakdown and disruption of the normal host defense mechanisms. To further clarify their virulence, RGP-and KGP deficient mutants were constructed by gene disruption using suicide plasmid systems. The RGP-null mutant showed a remarkable loss of both the suppressive activity of PMN functions and the hemagglutinating activity observed with the wild-type strain, suggesting that RGP is responsible for these activities of the organism. The RGPnull mutant also showed the defect in fimbriation and processing of prefimbrilin and the 75-kDa surface protein precursor, suggesting that RGP is involved in processing and translocation of certain cell surface proteins of the organism. On the other hand, the KGP-deficient mutant, like the wild type strain, strongly retained the abilities to suppress the PMN bactericidal activity and to hemagglutinate, but it could not form the black pigmentation of colonies when grown in blood agar plate.
P. gingivalis is known to stockpile heme from hemoglobin in blood agar, resulting in the black pigmentation. Therefore, KGP appeared to be involved in the adsorption and degradation of hemoglobin and the heme accumulation in the organism.
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