Protein Disulfide Isomerase A4 (PDIA4)

Protein Disulfide Isomerase A4is 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.

The 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 posttranslational modification disulfide exchange. Such exchange reactions can occur intramolecularly, leading to the rearrangement of disulfide bonds in a single protein.