Journal
BIOLOGICAL CHEMISTRY
Volume 382, Issue 6, Pages 979-986Publisher
WALTER DE GRUYTER & CO
DOI: 10.1515/BC.2001.123
Keywords
alkyl hydroperoxide reductase; antioxidant; oxidative stress; peroxidase; selenoprotein
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A strongly Se-75-labeled 22 kDa protein detected previously showed in its N-terminal sequence the highest similarity to the family of thiol-dependent peroxidases, now called peroxiredoxins. The respective gene prxU was cloned and analyzed. prxU encodes a protein of 203 amino acids (22 470 Da) and contains an in-frame UGA codon (selenocysteine) at the position of the so far strictly conserved and catalytically active Cys47. The second conserved cysteine present in 2-Cys peroxiredoxins was replaced by alanine. Heterologous expression of the Eubacterium acidaminophilum PrxU as a recombinant selenoprotein in Escherichia coli was not possible. A cysteine-encoding mutant gene, prxU47C, containing UGC instead of UGA was strongly expressed. This recombinant PrxU47C mutant protein was purified to homogeneity by its affinity tag, but was not active as a thiol-dependent peroxidase. The identification of prxU reveals that the limited class of natural selenoproteins may in certain organisms also include isoenzymes of peroxiredoxins, previously only known as non-selenoproteins containing catalytic cysteine residues.
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