Molecular mechanism of acquisition and storage of iron from oral environment by the periodontopathogen Porphyromonas gingivalis.

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Porphyromonas gingivalis is an oral anaerobic Gram-negative microorganism which is implicated as an important etiological agent of adult periodontal disease.P.gingivalis is asaccharolytic and highly proteolytic. Major extracellular and cell-associated proteinases of P.gingivalis are now found to consist of arginine-specific proteinase (Rgp) and lysine-specific proteinase (Kgp). We found that the hemoglobin receptor protein (HbR) of P.gingivalis was intragenically encoded as HGP15 domain region by rgpA, kgp and hagA genes. We have constructed a number of mutant strains with combination of these genes. The kgp mutant showed less-pigmented when grown on the blood agar plate. The rgpA rgpB double (Rgp-null) mutant was found to be unfimbriated, which is consistent with the result that Rgp was directly involved in maturation of the fimA-fimbriae and the surface 75 kDa protein. The rgpA rgpB kgp triple (Rgp Kgp-null) mutant could not grow in a minimal medium containing bovine serum albumin as … More the sole carbon/energy source, indicating that these proteinases are particularly important for degradation of environmental proteins to produce utilizable peptides. In addition, this triple mutant showed no hemoglobin adsorption or hemagglutination, indicating that the HbR protein encoded by HGP15 region and hemagglutinins encoded by HGP44, HGP17 and HGP27 regions are responsible for these two properties, respectively. We also found that lactoferrin could bind to the HbR protein. The interaction of lactoferrin with HbR led to the release of HbR from the cell surface of P.gingivalis. P.gingivalis could not utilize lactoferrin for its growth as an iron source and, in contrast, lactoferrin inhibited the growth of the bacterium in a rich medium containing hemoglobin as the sole iron source. These results suggest that lactoferrin has a bacteriostatic action on P.gingivalis by binding HbR, removing it from the cell surface, and consequently disrupting the iron uptake system from hemoglobin. Less