Inhibitory effect of human α_2-plasmin inhibitor and it's intensified compound by S-nitrosylation on the activity of arginine-specific cysteine proteinase from Porphyromonas gingivalis.

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We investigated the effect of human α_2-plasmin inhibitor (α_2PI) and S-nitrosylated α_2-plasmin inhibitor (S-NO-α_2PI) on the activity of arginine-specific cysteine proteinase (gingipain, RGP) from Porphyromonas gingivalis, an aetiological bacterium of adult periodontitis, with the use of fluorogenic substrates. We discovered that human α_2PI as well as S-NO-α_2PI play a inhibitory effect to the RGP in a dose-dependent manner. The α_2PI, one of the members of serpin family, is well known as a specific inhibitor of plasmin, a typical serine proteinase. However, few studies have been reported concerning the inhibitory potency of humoral factors, such as α_1-protease inhibitor or α_2-macroglobulin, against cysteine proteinases especially RGP. In this study, we found a novel function of α_2PI as a potent inhibitor of RGP. The inhibitory potencies of the S-nitrosylated derivative against both human plasmin and RGP were slightly higher than those of the intact α_2PI. These results strongly suggest that S-NO-α_2PI is a useful tool for preventing the virulence of P. gingivalis.