Pyrococcus furiosus protein disulfide oxidoreductase (PfPDO)-like family, N-terminal TRX-fold subdomain; composed of proteins with similarity to PfPDO, a redox active thermostable protein believed to be the archaeal counterpart of bacterial DsbA and eukaryotic protein disulfide isomerase (PDI), which are both involved in oxidative protein folding. PfPDO contains two redox active CXXC motifs in two contiguous TRX-fold subdomains. The active site in the N-terminal TRX-fold subdomain is required for isomerase but not for reductase activity of PfPDO. The exclusive presence of PfPDO-like proteins in extremophiles may suggest that they have a special role in adaptation to extreme conditions.