title: Tryparedoxin peroxidases from Trypanosoma cruzi: high efficiency in the catalytic elimination of hydrogen peroxide and peroxynitrite.
abstract: During host cell infection, Trypanosoma cruzi parasites are exposed to reactive oxygen and nitrogen species. As part of their antioxidant defense systems, they express two tryparedoxin peroxidases (TXNPx), thiol-dependent peroxidases members of the peroxiredoxin family. In this work, we report a kinetic characterization of cytosolic (c-TXNPx) and mitochondrial (m-TXNPx) tryparedoxin peroxidases from T. cruzi. Both c-TXNPx and m-TXNPx rapidly reduced hydrogen peroxide (k=3.0 x 10⁷ and 6 x 10⁶ M⁻¹ s⁻¹ at pH 7.4 and 25 °C, respectively) and peroxynitrite (k=1.0 x 10⁶ and k=1.8 x 10⁷ M⁻¹ s⁻¹ at pH 7.4 and 25 °C, respectively). The reductive part of the catalytic cycle was also studied, and the rate constant for the reduction of c-TXNPx by tryparedoxin I was 1.3 x 10⁶ M⁻¹ s⁻¹. The catalytic role of two conserved cysteine residues in both TXNPxs was confirmed with the identification of Cys52 and Cys173 (in c-TXNPX) and Cys81 and Cys204 (in m-TXNPx) as the peroxidatic and resolving cysteines, respectively. Our results indicate that mitochondrial and cytosolic TXNPxs from T. cruzi are highly efficient peroxidases that reduce hydrogen peroxide and peroxynitrite, and contribute to the understanding of their role as virulence factors reported in vivo.
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay.
authors.forename: María Dolores
authors.initials: MD
authors.lastname: Piñeyro
authors.forename: Talia
authors.initials: T
authors.lastname: Arcari
authors.forename: Carlos
authors.initials: C
authors.lastname: Robello
authors.forename: Rafael
authors.initials: R
authors.lastname: Radi
authors.forename: Madia
authors.initials: M
authors.lastname: Trujillo
mesh_terms: D055162:Biocatalysis; D003600:Cytosol / Q000201:enzymology; D006861:Hydrogen Peroxide / Q000302:isolation & purification* / Q000378:metabolism*; D007700:Kinetics; D008928:Mitochondria / Q000201:enzymology; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D030421:Peroxynitrous Acid / Q000302:isolation & purification* / Q000378:metabolism*; D015800:Protozoan Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D014346:Trypanosoma brucei brucei / Q000201:enzymology; D014349:Trypanosoma cruzi / Q000166:cytology / Q000201:enzymology*
chemical_list: D015800:Protozoan Proteins; D030421:Peroxynitrous Acid; D006861:Hydrogen Peroxide; D010544:Peroxidases; C110959:tryparedoxin peroxidase