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Abstract
Thioredoxin reductases (TRs) are important redox regulatory enzymes, which control the redox state of thioredoxins. Mammals have cytosolic and mitochondrial TRs, which contain an essential selenocysteine residue and reduce cytosolic and mitochondrial thioredoxins. In addition, thioredoxin/glutathione reductase (TGR) was identified, which is a fusion of an N-terminal glutaredoxin domain and the TR module. Here we show that TGR is expressed at low levels in various tissues but accumulates in testes after puberty. The protein is particularly abundant in elongating spermatids at the site of mitochondrial sheath formation but is absent in mature sperm. We found that TGR can catalyze isomerization of protein and interprotein disulfide bonds and localized this function to its thiol domain. TGR targets include proteins that form structural components of the sperm, including glutathione peroxidase GPx4/PHGPx. Together, TGR and GPx4 can serve as a novel disulfide bond formation system. Both enzymes contain a catalytic selenocysteine consistent with the role of selenium in male reproduction.
Highlights
Thioredoxin reductases (TRs) are important redox regulatory enzymes, which control the redox state of thioredoxins
Initial studies suggested that a mitochondrial capsule selenoprotein mediated this effect, whereas recent studies revealed that this effect is because of the antioxidant and structural functions of GPx4 [13, 34]
Our study indicates a role for an additional selenoprotein, thioredoxin/glutathione reductase (TGR), in sperm maturation
Summary
TGR targets include proteins that form structural components of the sperm, including glutathione peroxidase GPx4/PHGPx. Together, TGR and GPx4 can serve as a novel disulfide bond formation system. TGR and GPx4 can serve as a novel disulfide bond formation system Both enzymes contain a catalytic selenocysteine consistent with the role of selenium in male reproduction. TRs are selenoproteins that contain a C-terminal penultimate selenocysteine (Sec) [2, 3], the 21st amino acid encoded by UGA These enzymes are key components of the thioredoxin system, which is one of major redox systems in cells. A functional characterization and localization of TGR revealed its disulfide bond isomerization activity and its close functional relationship to GPx4 These data implicated TGR in the process of sperm maturation
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