As a co-chaperone for HSPA5 it is required for proper folding, trafficking or degradation of proteins (PubMed:10827079, PubMed:15525676, PubMed:29706351). 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 (PubMed:15525676). May help recruiting HSPA5 and other chaperones to the substrate. Stimulates HSPA5 ATPase activity (PubMed:10827079). It is necessary for maturation and correct trafficking of PKD1 (PubMed:29706351). 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. Associated with the ER membrane in a C-terminally epitope-tagged construct. Widely expressed. By endoplasmic reticulum stress-inducing agents such as thapsigargin and tunicamycin. 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. Thr-188 was reported to be phosphorylated upon DNA damage by ATM or ATR; however as this position has been shown to be in the ER lumen, the in vivo relevance is not proven. The disease is caused by variants affecting the gene represented in this entry. PubMed:11584023 reported a cytosolic, as well as nuclear subcellular location. This result was obtained using an N-terminally GFP-tagged construct which most probably affected signal peptide-driven targeting to the ER. As a consequence, the in vivo revelance of the observed interaction with APOBEC1, a nuclear protein, is dubious. This holds true for the interaction with PWP1.