Catalyzes the rearrangement of -S-S- bonds in proteins. Part of a large chaperone multiprotein complex comprising DNAJB11, HSP90B1, HSPA5, HYOU, PDIA2, PDIA4, PDIA6, PPIB, SDF2L1, UGGT1 and very small amounts of ERP29, but not, or at very low levels, CALR nor CANX. Component of a complex containing at least CRELD2, MANF, MATN3 and PDIA4 (PubMed:23956175). Belongs to the protein disulfide isomerase family.