FIGURE 13.

Proposed function of PgDps. In in vivo conditions when iron is scarce and heme is the only iron source, various heme transport receptors are up-regulated and extracellular heme is imported (1) into the cell. The fate of intracellular heme in P. gingivalis is currently not known, but most likely the iron and porphyrin will be separated (2) for utilization in other cellular pathways. In response to the presence of intracellular heme and iron, PgDps is expressed and self-assembled (3) into dodecameric forms. Intracellular ferrous iron is converted to ferric iron by PgDps and is sequestered within the hollow core of the dodecamer, whereas heme is sequestered (4) on the surface of the complex. Binding of heme onto PgDps subsequently induces aggregation (5) of PgDps dodecamers, possibly via heme stacking/dimerization. Without the ferroxidase and sequestration function of PgDps, unbound ferrous iron and heme can produce free radicals in the presence of an oxidizing agent (6) leading to DNA damage.