Nitric oxide inhibits cruzipain, the major papain-like cysteine proteinasefrom Trypanosoma cruzi

Nitric oxide (NO) is a pluripotent regulatory molecule showing, among other s, an antiparasitic activity. Moreover, NO inhibits cysteine proteinase act ion by nitrosylating the Cys catalytic residue. In the present study, the i nhibitory effect of the substrate N-alpha-benzyloxycarbonyl-L-phenylalanyl- L-arginine-(7-amino-4-methylcoumarin) and of NO on the catalytic activity o f cruzipain, the major papain-like cysteine proteinase from Trypanosoma cru zi (the hemoflagellate protozoan parasite which causes the American trypano somiasis), is reported. In particular, NO-donors S-nitroso-glutathione (GSN O), (+/-)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (NOR-3), 3-mo rpholinosydnonimine (SIN-1), S-nitroso-acetyl-penicillamine (SNAP), and sod ium nitroprusside (SNP) dose-dependently inhibited cruzipain, this effect b eing likely attributable to the S-nitrosylation of the Cys25 catalytic resi due. These results were analyzed in parallel with those concerning the inhi bitory effect of the substrate and of NO on the catalytic activity of falci pain, the cruzipain-homologous cysteine proteinase from Plasmodium falcipar um. The modulation of the cruzipain and falcipain activity by NO may be rel evant in developing new strategies against T. cruzi and P. falciparum in hu man host. As a whole, the NO-mediated S-nitrosylation of pathogenic viral, bacterial, fungal, and parasitic cysteine proteinases may represent a gener al mechanism of antimicrobial and antiparasitic host defences, (C) 2000 Aca demic Press.