Differential binding of Blood Group antigens by Porphyromonas gingivalis

OBJECTIVE:

Porphyromonas gingivalis is a major pathogen in chronic periodontitis. The organism has the capacity to attach to oral epithelia and to bind red blood cells (RBCs).

These properties help to localize the organism and, by trapping RBCs, to extract haem to support the essential iron and porphyrin requirements of the organism.

As oral epithelia and RBCs express ABH antigens, the objective of this study was to determine if these antigens are recognized by the haemagglutinin domain of the lysine gingipain (Kgp) as the first step in binding.

Methods:

The haemagglutinin domain of Kgp of P.gingivalis (KPAD), biovar W83, was cloned, expressed and purified. To specify the region responsible for the direct binding to Blood Group antigens, recombinant domains within KPAD were also expressed.

For recognition of ABH antigens, the purified recombinant polypeptides were tested in ELISA format against biotinylated Blood Group H oligosaccharide. Biotinylated Lewis-b antigen (homologue of H antigen) was used as control.

Results:

Preliminary data provided evidence to implicate the KPAD in Blood Group binding. High affinity binding to H antigen was localized in the c-terminal region of the KPAD (dissociation constant: 230nM).

The haemagglutinin domain could discriminate the single fucose in Lewis-b with high affinity binding to H antigen and low affinity binding to Lewis-b.

Conclusion:

The data demonstrate a new function for KPAD.

There is clear evidence that binding of KPAD is specific for ABH antigens as Lewis-b that is also expressed by epithelial cells does not show high affinity binding.

It is proposed that ABH binding is an early event in localization of the organism to epithelial surfaces and in trapping RBCs.

Preliminary data indicate that differences between four structural variants of Kgp are related to differentiatial binding of ABH antigens. This could explain individual susceptibility to colonization by different strains of P. gingivalis.