As a co-chaperone for HSPA5 it is required for proper folding, trafficking or degradation of proteins. Binds directly to both unfolded proteins that are substrates for ERAD and nascent unfolded peptide chains, but dissociates from the HSPA5-unfolded protein complex before folding is completed. May help recruiting HSPA5 and other chaperones to the substrate. Stimulates HSPA5 ATPase activity. It is necessary for maturation and correct trafficking of PKD1. 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. Binds to denatured substrates in an ATP-independent manner. Interacts via the J domain with HSPA5 in an ATP-dependent manner (By similarity). Pancreas. Contains high-mannose Endo H-sensitive carbohydrates. Cys-169, Cys-171, Cys-193 and Cys-196 form intramolecular disulfide bonds. The preferential partner for each Cys is not known (By similarity).