Kinetics and Redox-Sensitive Oligomerisation Reveal Negative Subunit Cooperativity in Tryparedoxin Peroxidase of Trypanosoma brucei brucei

H. Budde, L. Flohé, H.-J. Hecht, B. Hofmann, M. Stehr, J. Wissing und H. Lünsdorf

Abstract

Tryparedoxin peroxidases (TXNPx) are peroxiredoxintype enzymes that detoxify hydroperoxides in trypanosomatids. Reduction equivalents are provided by trypanothione [T(SH)2] via tryparedoxin (TXN). The T(SH)2-dependent peroxidase system was reconstituted from TXNPx and TXN of T. brucei brucei (TbTXNPx and TbTXN). TbTXNPx efficiently reduces organic hydroperoxides and is specifically reduced by TbTXN, less efficiently by thioredoxin, but not by glutathione (GSH) or T(SH)2. The kinetic pattern does not comply with a simple rate equation but suggests negative cooperativity of reaction centers. Gel permeation of oxidized TbTXNPx yields peaks corresponding to a decamer and higher aggregates. Electron microscopy shows regular ring structures in the decamer peak. Upon reduction, the rings tend to depolymerise forming openchain oligomers. Co-oxidation of TbTXNPx with TbTXNC43S yields a dead-end intermediate mimicking the catalytic intermediate. Its size complies with a stoichiometry of one TXN per subunit of TXNPx. Electron microscopy of the intermediate displays pentangular structures that are compatible with a model of a decameric TbTXNPx ring with ten bound TbTXN molecules. The redox-dependent changes in shape and aggregation state, the kinetic pattern and molecular models support the view that, upon oxidation of a reaction center, other subunits adopt a conformation that has lower reactivity with the hydroperoxide.

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Biological Chemistry keeps you up-to-date with the latest advances in the molecular life sciences. The journal publishes Research Articles, Short Communications, Reviews and Minireviews. Areas include: general biochemistry/pathobiochemistry, structural biology, molecular and cellular biology, genetics and epigenetics, virology, molecular medicine, plant molecular biology/biochemistry and novel experimental methodologies.

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