title: Substrate specificity, localization, and essential role of the glutathione peroxidase-type tryparedoxin peroxidases in Trypanosoma brucei.
abstract: Trypanosoma brucei, the causative agent of African sleeping sickness, encodes three nearly identical cysteine homologues of the classical selenocysteine-containing glutathione peroxidases. Although one of the sequences, peroxidase III, carries both putative mitochondrial and glycosomal targeting signals, the proteins are detectable only in the cytosol and mitochondrion of mammalian bloodstream and insect procyclic T. brucei. The enzyme is a trypanothione/tryparedoxin peroxidase as are the 2 Cys-peroxiredoxins of the parasite. Hydrogen peroxide, thymine hydroperoxide, and linoleic acid hydroperoxide are reduced with second order rate constants of 8.7 x 10(4), 7.6 x 10(4), and 4 x 10(4) m(-1) s(-1), respectively, and represent probable physiological substrates. Phosphatidylcholine hydroperoxide is a very weak substrate and, in the absence of Triton X-100, even an inhibitor of the enzyme. The substrate preference clearly contrasts with that of the closely related T. cruzi enzyme, which reduces phosphatidylcholine hydroperoxides but not H(2)O(2). RNA interference causes severe growth defects in bloodstream and procyclic cells in accordance with the peroxidases being essential in both developmental stages. Thus, the cellular functions of the glutathione peroxidase-type enzymes cannot be taken over by the 2 Cys-peroxiredoxins that also occur in the cytosol and mitochondrion of the parasite.
authors.affiliation: Biochemie-Zentrum der Universität Heidelberg, Germany.
authors.forename: Tanja
authors.initials: T
authors.lastname: Schlecker
authors.forename: Armin
authors.initials: A
authors.lastname: Schmidt
authors.forename: Natalie
authors.initials: N
authors.lastname: Dirdjaja
authors.forename: Frank
authors.initials: F
authors.lastname: Voncken
authors.forename: Christine
authors.initials: C
authors.lastname: Clayton
authors.forename: R Luise
authors.initials: RL
authors.lastname: Krauth-Siegel
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D003600:Cytosol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005979:Glutathione Peroxidase / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007700:Kinetics; D008041:Linoleic Acids / Q000494:pharmacology; D008054:Lipid Peroxides / Q000494:pharmacology; D008928:Mitochondria / Q000378:metabolism; D017830:Octoxynol / Q000494:pharmacology; D010544:Peroxidases / Q000737:chemistry* / Q000502:physiology*; D010713:Phosphatidylcholines / Q000737:chemistry; D015800:Protozoan Proteins / Q000737:chemistry* / Q000502:physiology*; D034622:RNA Interference; D011994:Recombinant Proteins / Q000737:chemistry; D013347:Subcellular Fractions / Q000378:metabolism; D013379:Substrate Specificity; D013941:Thymine / Q000737:chemistry; D013997:Time Factors; D014162:Transfection; D014346:Trypanosoma brucei brucei / Q000201:enzymology*
chemical_list: D008041:Linoleic Acids; D008054:Lipid Peroxides; D010713:Phosphatidylcholines; D015800:Protozoan Proteins; D011994:Recombinant Proteins; C057590:phosphatidylcholine hydroperoxide; C008285:linoleic acid hydroperoxide; D017830:Octoxynol; D006861:Hydrogen Peroxide; D010544:Peroxidases; C110959:tryparedoxin peroxidase; D005979:Glutathione Peroxidase; D013941:Thymine