Protein Disulfide Isomerase (PDI)

Protein disulfide isomerase or PDI is an enzyme in the endoplasmic reticulum in eukaryotes that catalyzes the formation and breakage of disulfide bonds between cysteine residues within proteins as they fold. Protein disulfide isomerases (EC 5.3.4.1), such as PDIP, are endoplasmic reticulum (ER) resident proteins that catalyze protein folding and thiol-disulfide interchange reactions. Desilva et al. (1996) cloned PDIP from an insulinoma subtraction cDNA library. The deduced 511-amino acid protein has a calculated molecular mass of about 56.6 kD and contains 2 thioredoxin-like catalytic sites, a C-terminal ER retention sequence (KEEL), and 3 potential N-glycosylation sites. PDIP shares about 46% identity with bovine, mouse, rabbit, and human PDIs . Northern blot analysis detected a 2.0-kb transcript expressed exclusively in pancreas.