Structural basis for a distinct catalytic mechanism in Trypanosoma brucei tryparedoxin peroxidase

Trypanosoma brucei, the causative agent of African sleeping sickness, encodes three cysteine homologues (Px I-III) of classical selenocysteine-containing glutathione peroxidases. The enzymes obtain their reducing equivalents from the unique trypanothione (bis(glutathionyl)spermidine)/tryparedoxin system. During catalysis, these tryparedoxin peroxidases cycle between an oxidized form with an intramolecular disulfide bond between Cys(47) and Cys(95) and the reduced peroxidase with both residues in the thiol state. Here we report on the three-dimensional structures of oxidized T. brucei Px III at 1.4A resolution obtained by x-ray crystallography and of both the oxidized and the reduced protein determined by NMR spectroscopy. Px III is a monomeric protein unlike the homologous poplar thioredoxin peroxidase (TxP). The structures of oxidized and reduced Px III are essentially identical in contrast to what was recently found for TxP. In Px III, Cys(47), Gln(82), and Trp(137) do not form the catalytic triad observed in the selenoenzymes, and related proteins and the latter two residues are unaffected by the redox state of the protein. The mutational analysis of three conserved lysine residues in the vicinity of the catalytic cysteines revealed that exchange of Lys(107) against glutamate abrogates the reduction of hydrogen peroxide, whereas Lys(97) and Lys(99) play a crucial role in the interaction with tryparedoxin

The silicon trypanosome

African trypanosomes have emerged as promising unicellular model organisms for the next generation of systems biology. They offer unique advantages, due to their relative simplicity, the availability of all standard genomics techniques and a long history of quantitative research. Reproducible cultivation methods exist for morphologically and physiologically distinct life-cycle stages. The genome has been sequenced, and microarrays, RNA-interference and high-accuracy metabolomics are available. Furthermore, the availability of extensive kinetic data on all glycolytic enzymes has led to the early development of a complete, experiment-based dynamic model of an important biochemical pathway. Here we describe the achievements of trypanosome systems biology so far and outline the necessary steps towards the ambitious aim of creating a , a comprehensive, experiment-based, multi-scale mathematical model of trypanosome physiology. We expect that, in the long run, the quantitative modelling enabled by the Silicon Trypanosome will play a key role in selecting the most suitable targets for developing new anti-parasite drugs

Stress-induced Protein S-Glutathionylation and S-Trypanothionylation in African Trypanosomes – a Quantitative Redox Proteome and Thiol Analysis:Protein S-Thiolation in Trypanosomes

Aims: Trypanosomatids have a unique trypanothione-based thiol redox metabolism. The parasite-specific dithiol is synthesized from glutathione and spermidine, with glutathionylspermidine as intermediate catalyzed by trypanothione synthetase. In this study, we address the oxidative stress response of African trypanosomes with special focus on putative protein S-thiolation. Results: Challenging bloodstream Trypanosoma brucei with diamide, H2O2 or hypochlorite results in distinct levels of reversible overall protein S-thiolation. Quantitative proteome analyses reveal 84 proteins oxidized in diamide-stressed parasites. Fourteen of them, including several essential thiol redox proteins and chaperones, are also enriched when glutathione/glutaredoxin serves as a reducing system indicating S-thiolation. In parasites exposed to H2O2, other sets of proteins are modified. Only three proteins are S-thiolated under all stress conditions studied in accordance with a highly specific response. H2O2 causes primarily the formation of free disulfides. In contrast, in diamide-treated cells, glutathione, glutathionylspermidine, and trypanothione are almost completely protein bound. Remarkably, the total level of trypanothione is decreased, whereas those of glutathione and glutathionylspermidine are increased, indicating partial hydrolysis of protein-bound trypanothione. Depletion of trypanothione synthetase exclusively induces protein S-glutathionylation. Total mass analyses of a recombinant peroxidase treated with T(SH)2 and either diamide or hydrogen peroxide verify protein S-trypanothionylation as stable modification. Innovation: Our data reveal for the first time that trypanosomes employ protein S-thiolation when exposed to exogenous and endogenous oxidative stresses and trypanothione, despite its dithiol character, forms protein-mixed disulfides. Conclusion: The stress-specific responses shown here emphasize protein S-trypanothionylation and S-glutathionylation as reversible protection mechanism in these parasites. Antioxid. Redox Signal. 27, 517-533

In Vitro and In Silico Analysis of New n-Butyl and Isobutyl Quinoxaline-7-carboxylate 1,4-di-N-oxide Derivatives against Trypanosoma cruzi as Trypanothione Reductase Inhibitors

American trypanosomiasis is a worldwide health problem that requires attention due to ineffective treatment options. We evaluated n-butyl and isobutyl quinoxaline-7-carboxylate 1,4-di-N-oxide derivatives against trypomastigotes of the Trypanosoma cruzi strains NINOA and INC-5. An in silico analysis of the interactions of 1,4-di-N-oxide on the active site of trypanothione reductase (TR) and an enzyme inhibition study was carried out. The n-butyl series compound identified as T-150 had the best trypanocidal activity against T. cruzi trypomastigotes, with a 13% TR inhibition at 44 μM. The derivative T-147 behaved as a mixed inhibitor with Ki and Ki' inhibition constants of 11.4 and 60.8 µM, respectively. This finding is comparable to the TR inhibitor mepacrine (Ki = 19 µM)

In vivo anti-chagas vinylthio-, vinylsulfinyl-, and vinylsulfonylbenzofuroxan derivatives

New benzofuroxans were developed and studied as antiproliferative Trypanosoma cruzi agents. Compounds displayed remarkable in vitro activities against different strains, Tulahuen 2, CL Brener and Y. Its unspecific cytotoxicity was evaluated using human macrophages being not toxic at a concentration at least 8 times, and until 250 times, that of its T. cruzi IC50. Some biochemical pathways were studied, namely parasite respiration, cysteinyl active site enzymes and reaction with glutathione, as target for the mechanism of action. Not only T. cruzi respiration but also Cruzipain or trypanothione reductase were not affected, however the most active derivatives, the vinylsulfinyl- and vinylsulfonyl-containing benzofuroxans, react with glutathione in a redox pathway. Furthermore, the compounds showed good in vivo activities when they were studied in an acute murine model of Chagas' disease. The compounds were able to reduce the parasite loads of animals with fully established T. cruzi infections. © 2007 American Chemical Society.Peer Reviewe

Mono- and Dithiol Glutaredoxins in the Trypanothione-Based Redox Metabolism of Pathogenic Trypanosomes

SIGNIFICANCE: Glutaredoxins are ubiquitous small thiol proteins of the thioredoxin-fold superfamily. Two major groups are distinguished based on their active sites: the dithiol (2-C-Grxs) and the monothiol (1-C-Grxs) glutaredoxins with a CXXC and a CXXS active site motif, respectively. Glutaredoxins are involved in cellular redox and/or iron sulfur metabolism. Usually their functions are closely linked to the glutathione system. Trypanosomatids, the causative agents of several tropical diseases, rely on trypanothione as principal low molecular mass thiol, and their glutaredoxins readily react with the unique bis(glutathionyl) spermidine conjugate. RECENT ADVANCES: Two 2-C-Grxs and three 1-C-Grxs have been identified in pathogenic trypanosomatids. The 2-C-Grxs catalyze the reduction of glutathione disulfide by trypanothione and display reductase activity towards protein disulfides, as well as protein-glutathione mixed disulfides. In vitro, all three 1-C-Grxs as well as the cytosolic 2-C-Grx of Trypanosoma brucei can complex an iron-sulfur cluster. Recently the structure of the 1-C-Grx1 has been solved by NMR spectroscopy. The structure is very similar to those of other 1-C-Grxs, with some differences in the loop containing the conserved cis-Pro and the surface charge distribution. CRITICAL ISSUES: Although four of the five trypanosomal glutaredoxins proved to coordinate an iron-sulfur cluster in vitro, the physiological role of the mitochondrial and cytosolic proteins, respectively, has only started to be unraveled. FUTURE DIRECTIONS: The use of trypanothione by the glutaredoxins has established a novel role for this parasite-specific dithiol. Future work should reveal if these differences can be exploited for the development of novel antiparasitic drugs

Privileged structure-guided synthesis of quinazoline derivatives as inhibitors of trypanothione reductase

Novel quinazoline-type compounds were designed as inhibitors of the parasite specific enzyme trypanothione reductase (TR), and their biological activities were evaluated. Some of our compounds inhibited TR, showed selectivity for TR over human glutathione reductase, and inhibited parasite growth in vitro. We propose that the quinazoline framework is a privileged structure that can be purposely modified to design novel TR inhibitors. Furthermore, the use of privileged motifs might emerge as an innovative approach to antiparasitic lead candidate

Glyoxalase II does not support methylglyoxal detoxification but serves as a general trypanothione thioesterase in African trypanosomes

Glyoxalase I and II form a ubiquitous glutathione-dependent pathway for the detoxification of reactive and mutagenic ketoaldehydes. Methylglyoxal produced as spontaneous by-product of glycolysis is probably the main physiological substrate. Consequently, African trypanosomes with their exorbitant glucose turnover were expected to have a most efficient detoxification system. Trypanosoma brucei possesses a trypanothione [bis(glutathionyl)spermidine]-dependent glyoxalase II but lacks a glyoxalase I gene. Methylglyoxal reductase as well as dehydrogenase activities are negligible. However, the concentrations of methylglyoxal and advanced glycation end products in the parasites are similar to those in different mammalian cells and the mechanism of methylglyoxal elimination remains elusive. Glyoxalase II is an abundant protein. Overexpression of the gene as well as RNA interference in bloodstream and procyclic cells did not result in a growth phenotype. Deletion of both alleles in procyclic parasites revealed that the enzyme is not essential at least under culture conditions. Recombinant glyoxalase II hydrolyzed the trypanothione-thioesters of methylglyoxal, glyoxal and 4,5-dioxovalerate, substrates of the classical glyoxalase system, with high efficiency. The absence of a glyoxalase I, however, renders these thioesters unlikely as physiological substrates. Here we show that trypanothione-thioesters can be generated from the respective coenzyme A derivative by transesterification. S-Acetyl- and S-prop ionyl trypanothione obtained by this spontaneous reaction proved to be excellent substrates of T brucei glyoxalase II. This offers a function for the parasite glyoxalase II as general trypanothione thioesterase independent of ketoaldehyde detoxification. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved