<p>Several biological processes regulate the activity of target proteins through changes in the redox state of thiol groups (S2 to SH2), where a hydrogen donor is linked to an intermediary disulphide protein. Such processes include the ferredoxin/thioredoxin system, the NADP/thioredoxin system, and the glutathione/glutaredoxin system [<cite idref="PUB00016292"/>]. Several of these disulphide proteins share a common structure, consisting of a three-layer alpha/beta/alpha core. Proteins that contain domains with a thioredoxin-like fold include:</p><p> <ul><li>Arsenate reductase (ArsC) [<cite idref="PUB00025947"/>]</li><li>Calsequestrin (contains three tandem repeats of this fold) [<cite idref="PUB00023289"/>]</li><li>Circadian oscillation regulator KaiB [<cite idref="PUB00015216"/>]</li><li>Disulphide bond isomerase DsbC and DsbG (C-terminal domain) [<cite idref="PUB00013324"/>, <cite idref="PUB00031997"/>]</li><li>Disulphide bond facilitator DsbA (contains an alpha-helical insertion) [<cite idref="PUB00023314"/>]</li><li>Endoplasmic reticulum protein ERP29 (N-terminal domain) [<cite idref="PUB00014099"/>]</li><li>Glutathione S-transferase (GST) (N-terminal domain) [<cite idref="PUB00039118"/>]</li><li>Mitochondrial ribosomal protein L51/S25/CI-B8 domain (variable positions for Cys residues in active site) [<cite idref="PUB00030888"/>]</li><li>Phosducin [<cite idref="PUB00032922"/>]</li><li>Protein disulphide isomerase (PDI) (contains two tandem repeats of this fold) [<cite idref="PUB00032776"/>]</li><li>Glutathione peroxidase-like enzymes [<cite idref="PUB00001337"/>]</li><li>Selenoprotein W-related [<cite idref="PUB00035459"/>]</li><li>SH3-binding glutamic acid-rich protein like (SH3BGR) (lacks both conserved Cys residues) [<cite idref="PUB00031286"/>]</li><li>Spliceosomal protein U5-15Kd [<cite idref="PUB00007371"/>]</li><li>Thioltransferases, including thioredoxin [<cite idref="PUB00032923"/>], glutaredoxon [<cite idref="PUB00024544"/>], hybrid peroxiredoxin hyPrx5 [<cite idref="PUB00029121"/>]</li><li>Thioredoxin-like 2Fe-2S ferredoxin [<cite idref="PUB00027201"/>]</li></ul> </p>