Platyhelminth Mitochondrial and Cytosolic Redox Homeostasis Is Controlled by a Single Thioredoxin Glutathione Reductase and Dependent on Selenium and Glutathione

Authors

Mariana Bonilla, Cátedra de Inmunología, Facultad de Química-Facultad de Ciencias, Instituto de Higiene, Universidad de la República, Avda. A. Navarro 3051, Piso 2, Montevideo 11600, Uruguay
Ana Denicola, Universidad de la República, Montevideo, Uruguay
Sergey V. Novoselov, University of Nebraska-LincolnFollow
Anton A. Turanov, University of Nebraska-LincolnFollow
Anna Protasio, Cátedra de Inmunología, Facultad de Química-Facultad de Ciencias, Instituto de Higiene, Universidad de la República
Darwin Izmendi, Cátedra de Inmunología, Facultad de Química-Facultad de Ciencias, Instituto de Higiene, Universidad de la República, Avda. A. Navarro 3051, Piso 2, Montevideo 11600, Uruguay
Vadim N. Gladyshev, University of Nebraska-LincolnFollow
Gustavo Salinas, Cátedra de Inmunología, Facultad de Química-Facultad de Ciencias, Instituto de Higiene, Universidad de la República, Avda. A. Navarro 3051, Piso 2, Montevideo 11600, Uruguay

Date of this Version

6-27-2008

Comments

Published in Journal of Biological Chemistry 283:26 (June 27, 2008), pp. 17898-17907; doi 10.1074/jbc.M710609200 Copyright © 2008 The American Society for Biochemistry and Molecular Biology, Inc. Used by permission. http://www.jbc.org/cgi/content/full/M710609200/DC1

Abstract

Platyhelminth parasites are a major health problem in developing countries. In contrast to their mammalian hosts, platyhelminth thiol-disulfide redox homeostasis relies on linked thioredoxin-glutathione systems, which are fully dependent on thioredoxin-glutathione reductase (TGR), a promising drug target. TGR is a homodimeric enzyme comprising a glutaredoxin domain and thioredoxin reductase (TR) domains with a C-terminal redox center containing selenocysteine (Sec). In this study, we demonstrate the existence of functional linked thioredoxin-glutathione systems in the cytosolic and mitochondrial compartments of Echinococcus granulosus, the platyhelminth responsible for hydatid disease. The glutathione reductase (GR) activity of TGR exhibited hysteretic behavior regulated by the [GSSG]/[GSH] ratio. This behavior was associated with glutathionylation by GSSG and abolished by deglutathionylation. The K_m and k_cat values for mitochondrial and cytosolic thioredoxins (9.5 μM and 131 s^-1, 34 μM and 197 s^-1, respectively) were higher than those reported for mammalian TRs. Analysis of TGR mutants revealed that the glutaredoxin domain is required for the GR activity but did not affect the TR activity. In contrast, both GR and TR activities were dependent on the Sec-containing redox center. The activity loss caused by the Sec-to-Cys mutation could be partially compensated by a Cys-to-Sec mutation of the neighboring residue, indicating that Sec can support catalysis at this alternative position. Consistent with the essential role of TGR in redox control, 2.5 μM auranofin, a known TGR inhibitor, killed larval worms in vitro. These studies establish the selenium- and glutathione-dependent regulation of cytosolic and mitochondrial redox homeostasis through a single TGR enzyme in platyhelminths.