Probable chaperone. Stimulates ATP hydrolysis and the folding of unfolded proteins mediated by HSPA1A/B (in vitro) (PubMed:24318877). Homodimer. The C-terminal section interacts with the C-terminal tail of OPRM1. Interacts also with SDIM1. Cytoplasmic according to PubMed:18837411 and membrane-associated according to PubMed:16542645. Expressed in heart, pancreas and skeletal muscle, and to a lesser extent in brain, placenta and liver. By heat shock.