Structure and mechanism of mammalian thioredoxin reductase: the active site is a redox-active selenolthiol/selenenylsulfide formed from the conserved cysteine-selenocysteine sequence.

@article{Zhong2000StructureAM,
  title={Structure and mechanism of mammalian thioredoxin reductase: the active site is a redox-active selenolthiol/selenenylsulfide formed from the conserved cysteine-selenocysteine sequence.},
  author={Liangwei Zhong and Elias S. J. Arn{\'e}r and Anne Holmgren},
  journal={Proceedings of the National Academy of Sciences of the United States of America},
  year={2000},
  volume={97 11},
  pages={
          5854-9
        }
}
Mammalian thioredoxin reductases (TrxR) are homodimers, homologous to glutathione reductase (GR), with an essential selenocysteine (SeCys) residue in an extension containing the conserved C-terminal sequence -Gly-Cys-SeCys-Gly. In the oxidized enzyme, we demonstrated two nonflavin redox centers by chemical modification and peptide sequencing: one was a disulfide within the sequence -Cys(59)-Val-Asn-Val-Gly-Cys(64), identical to the active site of GR; the other was a selenenylsulfide formed from… 

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References

SHOWING 1-10 OF 34 REFERENCES
Rat and Calf Thioredoxin Reductase Are Homologous to Glutathione Reductase with a Carboxyl-terminal Elongation Containing a Conserved Catalytically Active Penultimate Selenocysteine Residue*
TLDR
The bovine and rat thioredoxin reduct enzyme sequences revealed a close homology to glutathione reductase including the conserved active site sequence (Cys-Val-Asn- Val-Gly-Cys) and confirmed the identity of a previously published putative human thiOREDoxin reduCTase cDNA clone.
Molecular Cloning and Characterization of a Mitochondrial Selenocysteine-containing Thioredoxin Reductase from Rat Liver*
TLDR
The specific localization of TrxR2 in mitochondria, together with the previous identification of mitochondria-specific thioredoxin and thiOREDoxin-dependent peroxidase, suggest that these three proteins provide a primary line of defense against H2O2 produced by the mitochondrial respiratory chain.
Mutagenesis of structural half-cystine residues in human thioredoxin and effects on the regulation of activity by selenodiglutathione.
TLDR
Results clearly showed that noncatalytic cysteine residues in hTrx were oxidized accompanied by dimerization and inactivation, which is believed to be the major metabolite of inorganic selenium compounds in mammalian tissues.
Redox Regulation of Cell Signaling by Selenocysteine in Mammalian Thioredoxin Reductases*
TLDR
The generation of reactive oxygen species in a human carcinoma cell line was shown to result in both the oxidation of the selenocysteine in TR1 and a subsequent increase in the expression of this enzyme, supporting an essential role for mammalian TR isozymes in redox-regulated cell signaling.
A hypothesis on the catalytic mechanism of the selenoenzyme thioredoxin reductase.
TLDR
The working hypothesis is proposed that the penultimate Cys-Sec pair (Sec is selenocysteine), located on a flexible C-terminal arm, is in redox communication with the active site disulphide}dithiol, and might even play an essential role in enzyme catalysis.
Human Placenta Thioredoxin Reductase
TLDR
In its physiological, NADPH-reduced form, the enzyme is strongly inhibited by organic gold compounds that are widely used in the treatment of rheumatoid arthritis; for auranofin, the K i was 4 nm when measured in the presence of 50 μmthioredoxin.
Selenocysteine, identified as the penultimate C-terminal residue in human T-cell thioredoxin reductase, corresponds to TGA in the human placental gene.
TLDR
The finding that T-cell TR is a selenoenzyme that contains Se in a conserved C-terminal region provides another example of the role of selenium in a major antioxidant enzyme system (i.e., thioredoxin-thiored toxin reductase), in addition to the well-known glutathione peroxidase enzyme system.
Mammalian Thioredoxin Reductase Is Irreversibly Inhibited by Dinitrohalobenzenes by Alkylation of Both the Redox Active Selenocysteine and Its Neighboring Cysteine Residue*
TLDR
A model for the interaction between TrxR and dinitrohalobenzenes is proposed, involving a functional FAD in the alkylated TrXR generating an anion nitroradical in a dinitrophenyl group, which in turn reacts with oxygen to generate superoxide.
Human Thioredoxin Reductase Directly Reduces Lipid Hydroperoxides by NADPH and Selenocystine Strongly Stimulates the Reaction via Catalytically Generated Selenols(*)
TLDR
Two novel pathways for the reduction and detoxification of lipid hydroperoxides, hydrogen peroxide, and organic hydroper oxides are suggested, i.e. the human thioredoxin reductase-dependent pathway and a coupled reduction in the presence of selenols or selenide resulting from the reduction ofselenocystine or seLenodiglutathione.
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