The effect of 95- (HRgpA) and 50-kDa
gingipain R (RgpB),
arginine-specific
cysteine proteinases from periodontopathogenic bacterium Porphyromonas gingivalis on human
prothrombin activation was investigated. Each
enzyme released
thrombin from
prothrombin in a dose- and time-dependent manner with the former
enzyme, containing adhesion domains, being 17-fold more efficient than the single chain RgpB. A close correlation between the generation of
fibrinogen clotting activity and amidolytic activity indicated that
alpha-thrombin was produced by
gingipains R, and this was confirmed by SDS-
polyacrylamide gel electrophoresis,
thrombin active site labeling, and amino-terminal sequence analysis of
prothrombin digestion fragments. Significantly, the catalytic efficiency of HRgpA to generate
thrombin (k(cat)/K(m) = 1.2 x 10(6) m(-)1 s(-)1) was 100-fold higher than that of RgpB (k(cat)/K(m) = 1.2 x 10(4) m(-)1 s(-)1). The superior
prothrombinase activity of HRgpA over RgpB correlates with the fact that only the former
enzyme was able to clot plasma, and kinetic data indicate that
prothrombin activation can occur in vivo. At P. gingivalis-infected
periodontitis sites HRgpA may be involved in the direct production of
thrombin and, therefore, in the generation of
prostaglandins and
interleukin-1, both have been found to be associated with the development and progression of the disease. Furthermore, by taking into account that the P. gingivalis bacterium has been immunolocalized in carotid
atherosclerotic plaques at
thrombus formation sites (Chiu, B. (1999) Am. Heart J. 138, S534-S536), our results indicate that bacterial
proteinases may potentially participate in the pathogenesis of
cardiovascular disease associated with
periodontitis.