PDIA4(Protein disulfide-isomerase A4) is also named as ERP70,ERP72 and belongs to the protein disulfide isomerase family. It catalyzes the rearrangement of -S-S- bonds in proteins. ERp72 is a soluble protein localized in the ER lumen and contains the COOH-terminal retention signal,KEEL. There are 6 cysteine residues in the amino acid sequences of mouse and human ERp72. All of the cysteine residues occur in the internal thioredoxin motif,CGHC. The full length protein has a signal peptide with 20 amino acid.