The selenium-independent inherent pro-oxidant NADPH oxidase activity of mammalian thioredoxin reductase and its selenium-dependent direct peroxidase activities. J Biol Chem 2010 Jul 09;285(28):21708-23
Date
05/12/2010Pubmed ID
20457604Pubmed Central ID
PMC2898413DOI
10.1074/jbc.M110.117259Scopus ID
2-s2.0-77954355103 (requires institutional sign-in at Scopus site) 56 CitationsAbstract
Mammalian thioredoxin reductase (TrxR) is an NADPH-dependent homodimer with three redox-active centers per subunit: a FAD, an N-terminal domain dithiol (Cys(59)/Cys(64)), and a C-terminal cysteine/selenocysteine motif (Cys(497)/Sec(498)). TrxR has multiple roles in antioxidant defense. Opposing these functions, it may also assume a pro-oxidant role under some conditions. In the absence of its main electron-accepting substrates (e.g. thioredoxin), wild-type TrxR generates superoxide (O ), which was here detected and quantified by ESR spin trapping with 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO). The peroxidase activity of wild-type TrxR efficiently converted the O adduct (DEPMPO/HOO(*)) to the hydroxyl radical adduct (DEPMPO/HO(*)). This peroxidase activity was Sec-dependent, although multiple mutants lacking Sec could still generate O . Variants of TrxR with C59S and/or C64S mutations displayed markedly reduced inherent NADPH oxidase activity, suggesting that the Cys(59)/Cys(64) dithiol is required for O generation and that O is not derived directly from the FAD. Mutations in the Cys(59)/Cys(64) dithiol also blocked the peroxidase and disulfide reductase activities presumably because of an inability to reduce the Cys(497)/Sec(498) active site. Although the bulk of the DEPMPO/HO(*) signal generated by wild-type TrxR was due to its combined NADPH oxidase and Sec-dependent peroxidase activities, additional experiments showed that some free HO(*) could be generated by the enzyme in an H(2)O(2)-dependent and Sec-independent manner. The direct NADPH oxidase and peroxidase activities of TrxR characterized here give insights into the full catalytic potential of this enzyme and may have biological consequences beyond those solely related to its reduction of thioredoxin.
Author List
Cheng Q, Antholine WE, Myers JM, Kalyanaraman B, Arnér ES, Myers CRAuthor
Balaraman Kalyanaraman PhD Professor in the Biophysics department at Medical College of WisconsinMESH terms used to index this publication - Major topics in bold
AnimalsBase Sequence
Electron Spin Resonance Spectroscopy
Gene Expression Regulation, Enzymologic
Humans
Hydroxyl Radical
Molecular Sequence Data
Mutation
NADPH Oxidases
Oxidants
Peroxidase
Pyrroles
Recombinant Proteins
Selenium
Thioredoxin-Disulfide Reductase
Thioredoxins