Reaction Mechanism and Regulation of Mammalian Thioredoxin/Glutathione Reductase

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• 作者：Qi-An Sun ; Dan Su ; Sergey V. Novoselov ; Bradley A. Carlson ; Dolph L. Hatfield ; and Vadim N. Gladyshev
• 刊名：Biochemistry
• 出版年：2005
• 出版时间：November 8, 2005
• 年：2005
• 卷：44
• 期：44
• 页码：14528 - 14537
• 全文大小：467K
• 年卷期：v.44,no.44(November 8, 2005)
• ISSN：1520-4995

文摘

Thioredoxin/glutathione reductase (TGR) is a recently discovered member of the selenoproteinthioredoxin reductase family in mammals. In contrast to two other mammalian thioredoxin reductases, itcontains an N-terminal glutaredoxin domain and exhibits a wide spectrum of enzyme activities. To elucidatethe reaction mechanism and regulation of TGR, we prepared a recombinant mouse TGR in the selenoproteinform as well as various mutants and individual domains of this enzyme. Using these proteins, we showedthat the glutaredoxin and thioredoxin reductase domains of TGR could independently catalyze reactionsnormally associated with each domain. The glutaredoxin domain is a monothiol glutaredoxin containinga CxxS motif at the active site, which could receive electrons from either the thioredoxin reductase domainof TGR or thioredoxin reductase 1. We also found that the C-terminal penultimate selenocysteine wasrequired for transfer of reducing equivalents from the thiol/disulfide active site of TGR to the glutaredoxindomain. Thus, the physiologically relevant NADPH-dependent activities of TGR were dependent on thisresidue. In addition, we examined the effects of selenium levels in the diet and perturbations inselenocysteine tRNA function on TGR biosynthesis and found that expression of this protein was regulatedby both selenium and tRNA status in liver, but was more resistant to this regulation in testes.