GRP78 (Glucose-regulated protein 78 kDa; also BiP and HSPA5) is a 72 kDa member of the heat shock protein 70 family of proteins. Intracellularly, GRP78 is an endoplasmic reticulum chaperone that participates in protein folding; extracellularly, it induces IL-10 production from T cells and interacts with Cripto to block TGF-beta signaling. Human GRP78 precursor is 654 amino acids (aa) in length. It contains an 18 aa signal sequence and a 636 aa mature region that shows a hydantoinase A region (aa 145‑245) and a C-terminal KDEL motif that is present on intracellular GRP78, but absent on secreted GRP78. There is alternative splicing in the signal sequence (aa 1‑10), and multiple single aa substitituion. Over aa 1‑654, human GRP78 is more than 97% aa identical to mouse and rat GRP78.
