Glutathione reductase and thioredoxin reductase at the crossroad: The structure of Schistosoma mansoni thioredoxin glutathione reductase

Abstract

Thioredoxin glutathione reductase (TGR) is a key flavoenzyme expressed by schistosomes that bridges two detoxification pathways crucial for the parasite survival in the host's organism. In this article we report the crystal structure (at 2.2 A resolution) of TGR from Schistosoma mansoni (SmTGR), deleted in the last two residues. The structure reveals the peculiar architecture of this chimeric enzyme: the small Glutaredoxin (Grx) domain at the N-terminus is joined to the large thioredoxin reductase (TR) one via an extended complementary surface, involving residues not conserved in the Grx superfamily; the TR domain interacts with an identical partner via its C-terminal domain, forming a dimer with a twisted "W" shape. Although lacking the penultimate Selenocysteine residue (Sec), the enzyme is still able to reduce oxidized glutathione. These data update the interpretation of the interdomain communication in TGR enzymes. The possible function of this enzyme in pathogenic parasites is discussed.

Mapping the Catalytic Cycle of Schistosoma mansoni Thioredoxin Glutathione Reductase by X-ray Crystallography

“…Functional analysis performed on SmTGR and on different TGRs proved that the penultimate Sec is essential for the reduction of thioredoxin and the glutaredoxin domain (6,12,15). Reduction of glutathione under physiological conditions is probably dependent on the redox exchange with glutaredoxin and thus is also inhibited in Sec-lacking enzymes, even though we observed residual GR activity in a C-terminally truncated variant of SmTGR (17). This residual activity is only observed in the SmTGR variant that lacks the C-terminal arm and is not shared by the full-length U597C mutant (see supplemental material); thus, we believe that in the WT enzyme the GR activity is mostly accomplished by the Grx domain.…”

“…The gene for full-length TGR, with the mutation U597C, was obtained starting from the gene of truncated SmTGR optimized for Escherichia coli expression (17), with appropriate DNA primers. The gene was cloned in a pGEX4T-1 commercial vector (GE Healthcare) and expressed in BL21(DE3) E. coli cells (Novagen).…”

“…Data analysis was performed with HKL2000 suite (19) indicating that all crystals belonged to the C2 space group, isomorphous to the SmTGR truncated form (17). Difference Fourier method was used to solve all structures, and refinements were performed using REFMAC5 (20).…”

“…The two domains work either coupled or independently to catalyze the reduction of a large number of oxidized substrates. The C-terminal tail of each subunit, which is close to the FAD active site of the adjacent subunit, contains the Sec residue (17).…”

Un nouvel espoir dans le traitement de la schistosomiase

“…Des travaux récents ont démontré que le composé K11777 (un inhibiteur de protéase de type vinylsulfone déjà utilisé en phase pré-clinique dans la maladie de Chagas 1 ) inhibe fortement l'activité de la cathepsine B1 de S. mansoni et dépendent l'une de la thiorédoxine, l'autre du glutathion, et qui font intervenir deux flavoenzymes (dépendantes du NADPH), la Thiorédoxine réductase (Trx) et la Glutathion réductase (GR), pour maintenir respectivement les taux adéquats de thiols à l'état réduit [14,15]. Chez le schistosome, ces deux voies sont confondues et dépendent d'une seule enzyme, la Thiorédoxine glutathion réductase (TGR) [9]. Le caractère essentiel de TGR pour la survie du parasite et les propriétés uniques de TGR ont fait d'elle une cible attractive pour de nouvelles chimiothérapies [10].…”