Linked thioredoxin-glutathione systems in platyhelminth parasites: alternative pathways for glutathione reduction and deglutathionylation.
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.
Cátedra de Inmunología, Facultad de Química, Instituto de Higiene, Universidad de la República, Avda A Navarro 3051, Piso 2, Montevideo 11600, Uruguay.
Mariana
M
Bonilla
Ana
A
Denicola
Stefano M
SM
Marino
Vadim N
VN
Gladyshev
Gustavo
G
Salinas
D000818:Animals; D002589:Cestoda / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism*; D015801:Helminth Proteins / Q000378:metabolism*; D006834:Hydrazines / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009247:NADH, NADPH Oxidoreductases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D010084:Oxidation-Reduction / Q000187:drug effects; D010455:Peptides / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects / Q000502:physiology; D013879:Thioredoxins / Q000378:metabolism*
C115239:3-(2-hydroxy-1-methyl-2-nitrosohydrazino)-N-methyl-1-propanamine; D015801:Helminth Proteins; D006834:Hydrazines; D009097:Multienzyme Complexes; D020030:Nitric Oxide Donors; D010455:Peptides; D013879:Thioredoxins; D009247:NADH, NADPH Oxidoreductases; C466433:thioredoxin glutathione reductase; D005978:Glutathione