title: Plasmodium falciparum 2-Cys peroxiredoxin reacts with plasmoredoxin and peroxynitrite.
abstract: Thioredoxin peroxidase 1 (TPx1) of the malarial parasite Plasmodium falciparum is a 2-Cys peroxiredoxin involved in the detoxification of reactive oxygen species and - as shown here - of reactive nitrogen species. As novel electron acceptor of reduced TPx1, we characterised peroxynitrite; the rate constant for ONOO- reduction by the enzyme (1 x 10(6) M(-1) s(-1) at pH 7.4 and 37 degrees C) was determined by stopped-flow measurements. As reducing substrate of TPx1, we identified - aside from thioredoxin - plasmoredoxin; this 22-kDa protein occurs only in malarial parasites. When studying the potential roles of Cys74 and Cys170 of Tpx1 in catalysis, as well as in oligomerisation behaviour, we found that replacement of Cys74 by Ala influenced neither the dimerisation nor enzymatic activity of TPx1. In the C170A mutant, however, the kcat/Km for reduced Trx as a substrate was shown to be approximately 50-fold lower and, in contrast to the wild-type enzyme, covalently linked dimers were not formed. For the catalytic cycle of TPx1, we conclude that oxidation of the peroxidatic Cys50 by the oxidising substrate is followed by the formation of an intermolecular disulfide bond between Cys50 and Cys170' of the second subunit, which is then attacked by an external electron donor such as thioredoxin or plasmoredoxin.
authors.affiliation: Interdisciplinary Research Centre, Justus-Liebig-University, D-35392 Giessen, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Nickel
authors.forename: Madia
authors.initials: M
authors.lastname: Trujillo
authors.forename: Stefan
authors.initials: S
authors.lastname: Rahlfs
authors.forename: Marcel
authors.initials: M
authors.lastname: Deponte
authors.forename: Rafael
authors.initials: R
authors.lastname: Radi
authors.forename: Katja
authors.initials: K
authors.lastname: Becker
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D007700:Kinetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000737:chemistry* / Q000235:genetics; D054464:Peroxiredoxins; D030421:Peroxynitrous Acid / Q000737:chemistry*; D010963:Plasmodium falciparum / Q000201:enzymology*; D015800:Protozoan Proteins / Q000737:chemistry*; D013879:Thioredoxins / Q000737:chemistry* / Q000145:classification
chemical_list: D015800:Protozoan Proteins; D030421:Peroxynitrous Acid; D013879:Thioredoxins; D010544:Peroxidases; D054464:Peroxiredoxins