Protein disulfide isomerase: the multifunctional redox chaperone of the endoplasmic reticulum.

Protein disulfide isomerase (PDI) is a protein-thiol oxidoreductase that catalyzes the oxidation, reduction and isomerization of protein disulfides. In the endoplasmic reticulum PDI catalyzes both the oxidation and isomerization of disulfides on nascent polypeptides. Under the reducing condition of the cytoplasm, endosomes and cell surface. PDI catalyzes the reduction of protein disulfides. At those locations, PDI has been demonstrated to participate in the regulation of reception function, cell-cell interaction, gene expression, and actin filament polymerization. These activities of PDI will be discussed, as well as its activity as a chaperone and subunit of prolyl 4-hydroxylase and microsomal triglyceride transfer protein.