Linked thioredoxin-glutathione systems in platyhelminth parasites: alternative pathways for glutathione reduction and deglutathionylation

J Biol Chem. 2011 Feb 18;286(7):4959-67. doi: 10.1074/jbc.M110.170761. Epub 2010 Nov 4.


In most organisms, thioredoxin (Trx) and/or glutathione (GSH) systems are essential for redox homeostasis and deoxyribonucleotide synthesis. Platyhelminth parasites have a unique and simplified thiol-based redox system, in which the selenoprotein thioredoxin-glutathione reductase (TGR), a fusion of a glutaredoxin (Grx) domain to canonical thioredoxin reductase domains, is the sole enzyme supplying electrons to oxidized glutathione (GSSG) and Trx. This enzyme has recently been validated as a key drug target for flatworm infections. In this study, we show that TGR possesses GSH-independent deglutathionylase activity on a glutathionylated peptide. Furthermore, we demonstrate that deglutathionylation and GSSG reduction are mediated by the Grx domain by a monothiolic mechanism and that the glutathionylated TGR intermediate is resolved by selenocysteine. Deglutathionylation and GSSG reduction via Grx domain, but not Trx reduction, are inhibited at high [GSSG]/[GSH] ratios. We found that Trxs (cytosolic and mitochondrial) provide alternative pathways for deglutathionylation and GSSG reduction. These pathways are operative at high [GSSG]/[GSH] and function in a complementary manner to the Grx domain-dependent one. Despite the existence of alternative pathways, the thioredoxin reductase domains of TGR are an obligate electron route for both the Grx domain- and the Trx-dependent pathways. Overall, our results provide an explanation for the unique array of thiol-dependent redox pathways present in parasitic platyhelminths. Finally, we found that TGR is inhibited by 1-hydroxy-2-oxo-3-(N-3-methyl-aminopropyl)-3-methyl-1-triazene (NOC-7), giving further evidence for NO donation as a mechanism of action for oxadiazole N-oxide TGR inhibitors. Thus, NO donors aimed at TGR could disrupt the entire redox homeostasis of parasitic flatworms.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cestoda / metabolism*
  • Glutathione / metabolism*
  • Helminth Proteins / metabolism*
  • Hydrazines / pharmacology
  • Multienzyme Complexes / antagonists & inhibitors
  • Multienzyme Complexes / metabolism*
  • NADH, NADPH Oxidoreductases / antagonists & inhibitors
  • NADH, NADPH Oxidoreductases / metabolism*
  • Nitric Oxide Donors / pharmacology
  • Oxidation-Reduction / drug effects
  • Peptides / metabolism
  • Protein Processing, Post-Translational / drug effects
  • Protein Processing, Post-Translational / physiology
  • Thioredoxins / metabolism*


  • 3-(2-hydroxy-1-methyl-2-nitrosohydrazino)-N-methyl-1-propanamine
  • Helminth Proteins
  • Hydrazines
  • Multienzyme Complexes
  • Nitric Oxide Donors
  • Peptides
  • Thioredoxins
  • NADH, NADPH Oxidoreductases
  • thioredoxin glutathione reductase
  • Glutathione