title: Inhibition of Schistosoma mansoni thioredoxin-glutathione reductase by auranofin: structural and kinetic aspects.
abstract: Schistosomiasis is a parasitic disease affecting over 200 million people currently treated with one drug, praziquantel. A possible drug target is the seleno-protein thioredoxin-glutathione reductase (TGR), a key enzyme in the pathway of the parasite for detoxification of reactive oxygen species. The enzyme is a unique fusion of a glutaredoxin domain with a thioredoxin reductase domain, which contains a selenocysteine (Sec) as the penultimate amino acid. Auranofin (AF), a gold-containing compound already in clinical use as an anti-arthritic drug, has been shown to inhibit TGR and to substantially reduce worm burden in mice. Using x-ray crystallography we solved (at 2.5 A resolution) the structure of wild type TGR incubated with AF. The electron density maps show that the actual inhibitor is gold, released from AF. Gold is bound at three different sites not directly involving the C-terminal Sec residue; however, because the C terminus in the electron density maps is disordered, we cannot exclude the possibility that gold may also bind to Sec. To investigate the possible role of Sec in the inactivation kinetics, we tested the effect of AF on a model enzyme of the same superfamily, i.e. the naturally Sec-lacking glutathione reductase, and on truncated TGR. We demonstrate that the role of selenium in the onset of inhibition by AF is catalytic and can be mimicked by an external source of selenium (benzeneselenol). Therefore, we propose that Sec mediates the transfer of gold from its ligands in AF to the redox-active Cys couples of TGR.
authors.affiliation: Department of Biochemical Sciences A. Rossi Fanelli, Sapienza University of Rome and Istituto Pasteur-Fondazione Cenci Bolognetti, P. Le Aldo Moro 5, 00185 Rome, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Angelucci
authors.forename: Ahmed A
authors.initials: AA
authors.lastname: Sayed
authors.forename: David L
authors.initials: DL
authors.lastname: Williams
authors.forename: Giovanna
authors.initials: G
authors.lastname: Boumis
authors.forename: Maurizio
authors.initials: M
authors.lastname: Brunori
authors.forename: Daniela
authors.initials: D
authors.lastname: Dimastrogiovanni
authors.forename: Adriana E
authors.initials: AE
authors.lastname: Miele
authors.forename: Frida
authors.initials: F
authors.lastname: Pauly
authors.forename: Andrea
authors.initials: A
authors.lastname: Bellelli
mesh_terms: D000818:Animals; D018501:Antirheumatic Agents / Q000737:chemistry* / Q000494:pharmacology; D001310:Auranofin / Q000737:chemistry* / Q000494:pharmacology; D002384:Catalysis; D018360:Crystallography, X-Ray / Q000379:methods; D003545:Cysteine / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation; D015801:Helminth Proteins / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000737:chemistry*; D009247:NADH, NADPH Oxidoreductases / Q000037:antagonists & inhibitors / Q000737:chemistry*; D010084:Oxidation-Reduction; D017434:Protein Structure, Tertiary; D012550:Schistosoma mansoni / Q000378:metabolism*; D012643:Selenium / Q000737:chemistry
chemical_list: D018501:Antirheumatic Agents; D015801:Helminth Proteins; D009097:Multienzyme Complexes; D001310:Auranofin; D009247:NADH, NADPH Oxidoreductases; C466433:thioredoxin glutathione reductase; D012643:Selenium; D003545:Cysteine