Protein disulfide isomerase

Protein disulfide isomerase or PDI (EC 5.3.4.1) is an enzyme in the endoplasmic reticulum in eukaryotes or periplasmic space of prokaryotes that catalyzes the formation and breakage of disulfide bonds between cysteine residues within proteins as they fold. This allows proteins to quickly find the correct arrangement of disulfide bonds in their fully folded state and therefore the enzyme acts to catalyze protein folding. Conversely, reduced (dithiol) form of PDI is able to catalyse a reduction of mispaired thiol residues of a particular substrate, acting as an isomerase. Therefore, PDI is capable of catalyzing the post-translational disulfide exchange. Such exchange reactions can occur intramolecularly, leading to the rearrangement of disulphide bonds in a single protein.

Another major function of PDI relates to its activity as a chaperone, i.e. it aids wrongly folded proteins to reach a correctly folded state without the aid of enzymatic disulfide

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