THE ROLE OF ARGININE DEIMINASE FROM STREPTOCOCCUS PYOGENES IN INHIBITION MACROPHAGES NITROGEN MONOXIDE (NO) SYNTHESIS

Abstract

The protective role of macrophages closely related to the production of bactericidal molecules, in which nitrogen monoxide (NO) play an important role. Arginine serves as a substrate for inducible NO synthase (iNOS) in course of NO production. Expression and activity of iNOS are regulated by the availability of the substrate (arginine) in the intercellular space. The bacterial enzyme arginine deiminase also uses arginine as a substrate, causing its deficiency for host cells. The aim of this study was to confirm the possible role of arginine deiminase from S. pyogenes in inhibiting NO synthesis by macrophages. For this purpose, a comparative study was made of the effect on the synthesis of NO by macrophages of the products of destruction of two strains: the initial S. pyogenes M49-16 and the isogenic mutant S. pyogenes M49-16 delArcA with the inactivated arginine deiminase gene (arcA). It has been shown that the ability of S. pyogenes M49-16 to inhibit production of NO by macrophages depends on its arginine deiminase activity because the isogenous mutant of S. pyogenes M49-16 delArcA with the inactivated gene arcA has lost its ability to inhibit NO synthesis. This allows us to consider the effects of S. pyogenes M49-16 as effects of arginine deiminase. An analysis of the inhibitory mechanisms of the enzyme showed that suppression of NO synthesis was not associated with the effect of destruction products of S. pyogenes M49-16 on the viability of macrophages. According to data of flow cytometry, incubation of cells in the presence of S. pyogenes destruction products of the original and mutant strains did not affect the level of iNOS expression, i.e. did not alter synthesis or stability of this enzyme. At the same time, the decrease in NO production under the influence of the original S. pyogenes strain M49-16 correlated with a decrease in the content of arginine in the culture medium. When exogenous arginine to the culture medium was added, the effect of the original strain of the suppression of NO production was declined. This confirms that the depletion of arginine is the main mechanism of the inhibitory effect of arginine deiminase on the production of NO by macrophages. The deficiency of NO production in the course of streptococcal infection can lead to a weakening of bactericidal activity of macrophages and to a decrease in the effectiveness of antimicrobial protection.