This is the C-terminal domain of 1-Cys peroxiredoxin (1-cysPrx), a member of the peroxiredoxin superfamily which protect cells against membrane oxidation through glutathione (GSH)-dependent reduction of phospholipid hydroperoxides to corresponding alcohols [1]. The C-terminal domain is crucial for providing the extra cysteine necessary for dimerisation of the whole molecule. Loss of the enzyme's peroxidase activity is associated with oxidation of the catalytic cysteine, upstream of this domain; and glutathionylation, presumably through its disruption of protein structure, facilitates access for GSH, resulting in spontaneous reduction of the mixed disulfide to the sulfhydryl and consequent activation of the enzyme [2]. The domain is associated with family AhpC-TSA, Pfam:PF00578, which carries the catalytic cysteine.

1: Crystal structure of a novel human peroxidase enzyme at 2.0 A resolution. Choi HJ, Kang SW, Yang CH, Rhee SG, Ryu SE; Nat Struct Biol. 1998;5:400-406. PMID:9587003

2: Activation of the antioxidant enzyme 1-CYS peroxiredoxin requires glutathionylation mediated by heterodimerization with pi GST. Manevich Y, Feinstein SI, Fisher AB; Proc Natl Acad Sci U S A. 2004;101:3780-3785. PMID:15004285