• Molecules and Cells
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• v.39 no.8
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• pp.594-602
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• 2016

Alkyl hydroperoxide reductase subunit C from Pseudomonas aeruginosa PAO1 (PaAhpC) is a member of the 2-Cys peroxiredoxin family. Here, we examined the peroxidase and molecular chaperone functions of PaAhpC using a site-directed mutagenesis approach by substitution of Ser and Thr residues with Cys at positions 78 and 105 located between two catalytic cysteines. Substitution of Ser with Cys at position 78 enhanced the chaperone activity of the mutant (S78C-PaAhpC) by approximately 9-fold compared with that of the wild-type protein (WT-PaAhpC). This increased activity may have been associated with the proportionate increase in the high-molecular-weight (HMW) fraction and enhanced hydrophobicity of S78C-PaAhpC. Homology modeling revealed that mutation of $Ser^{78}$ to $Cys^{78}$ resulted in a more compact decameric structure than that observed in WT-PaAhpC and decreased the atomic distance between the two neighboring sulfur atoms of $Cys^{78}$ in the dimer-dimer interface of S78C-PaAhpC, which could be responsible for the enhanced hydrophobic interaction at the dimer-dimer interface. Furthermore, complementation assays showed that S78C-PaAhpC exhibited greatly improved the heat tolerance, resulting in enhanced1 survival under thermal stress. Thus, addition of Cys at position 78 in PaAhpC modulated the functional shifting of this protein from a peroxidase to a chaperone.

• Biomedical Science Letters
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• v.4 no.1
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• pp.1-9
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• 1998

A Corynebacterium diphtheriae iron-repressible gene dirA, that was homologous to TSA of Saccharomyces cerevisiae and AhpC subunit of Salmonella typhimurium alkyl hydroperoxide reductase, was amplified with PCR and expressed in E. coli. The DirA purified from the transformed E. coli crude extracts prevented the inactivation of enzyme caused by metal-catalyzed oxidation (MCO) system containing thiols but not by ascorbate/Fe$^{3+}$/$O_2$ MCO system. The DirA concentration, which inhibited the inactivation of glutamine synthetase by 50% (IC$_{50}$) against MCO system, was 0.12 mg/ml. The multimeric forms of DirA were converted to the monomeric form in SDS-PAGE under the thioredoxin system comprised of NADPH, Saccharomyces cerevisiae thioredoxin reductase, and thioredoxin. Also, DirA showed thioredoxin dependent peroxidase activity. All of these results were consistent with the characteristics of a thiol specific antioxidant (TSA) protein having two conserved cysteine residues.