The 78 kDa glucose regulated protein/BiP (GRP78) belongs to the family of ~70 kDa heat shock proteins (HSP70). GRP78 is localized in ER lumen as well as melanosomes (stage I to stage IV) where it facilitates protein folding/assembly, protein quality control, Ca2+ binding, and regulates ER stress signaling. GRP78 may also interact with mutant and misfolded proteins, marking them for degredation. GRP78 is found associated with diverse proteins including VDAC, MHC-I, Cripto and DnaJ-like protein MTJ-1. Because GRP78 is present on the surface of cancer cells but not on normal cells in vivo, it provide an exciting opportunity for cancer targeting.
