PDIb' family, ERp72 and ERp57 subfamily, second redox inactive TRX-like domain b'; ERp72 and ER57 are involved in oxidative protein folding in the ER, like PDI. They exhibit both disulfide oxidase and reductase functions, by catalyzing the formation of disulfide bonds of newly synthesized polypeptides and acting as isomerases to correct any non-native disulfide bonds. They also display chaperone activity to prevent protein aggregation and facilitate the folding of newly synthesized proteins. ERp57 contains two redox-active TRX (a) domains and two redox inactive TRX-like (b) domains. It shares the same domain arrangement of abb'a' as PDI, but lacks the C-terminal acid-rich region (c domain) that is present in PDI. ERp72 contains one additional redox-active TRX (a) domain at the N-terminus with a molecular structure of a"abb'a'. ERp57 interacts with the lectin chaperones, calnexin and calreticulin, and specifically promotes the oxidative folding of glycoproteins. ERp72 associates with several ER chaperones and folding factors to form complexes in the ER that bind nascent proteins. The b' domain of ERp57 is the primary binding site and is adapted for ER lectin association. Similarly, the b' domain of ERp72 is likely involved in substrate recognition.
Jiyao W et al.(2023). "The conserved domain database in 2023.",