ERP72, also known as PDIA4, is an endoplasmic reticulum luminal protein which belongs to the protein disulfide isomerase family. ERP72 is a stress protein and participates in the catalysis of protein-S-S-bond rearrangement. Both of PDIA4 and PDIA3 function as proteases, protein disulfide isomerases, phospholipases or an arrangement of these. ERP72 compose part of a large chaperone multiprotein complex comprising CABP1, DNAJB11, HSP90B1, HSPA5, HYOU, PDIA2, PDIA4, PPIB, SDF2L1, UGT1A1 and very small amounts of ERP29, but not, or at very low levels, CALR nor CANX.