|PDB structures||RCSB PDB PDBe PDBsum|
|Gene Ontology||AmiGO / EGO|
|protein disulfide isomerase family A, member 2|
|Locus||Chr. 16 p13.3|
|protein disulfide isomerase family A, member 3|
|Locus||Chr. 15 q15|
|protein disulfide isomerase family A, member 4|
|Locus||Chr. 7 q35|
|protein disulfide isomerase family A, member 5|
|Locus||Chr. 3 q21.1|
|protein disulfide isomerase family A, member 6|
|Locus||Chr. 2 p25.1|
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. 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.
PDI contains four thioredoxin-like domains, two of which retain the canonical CXXC motif. The reduced (that is, 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.
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 shuffling.
Oxidized PDI can catalyze the formation of a disulfide bridge. This reduces PDI and a protein called Ero1 oxidizes it again.
In the chloroplasts of the unicellular algae Chlamydomonas reinhardtii the PDI RB60 serves as a redox sensor component of an mRNA-binding protein complex implicated in the photo-regulation of the translation of psbA, the RNA encoding for the photosystem II core protein D1. PDI has also been suggested to play a role in the formation of regulatory disulfide bonds in chloroplasts.
PDI has been found to be involved in the breaking of bonds on the HIV gp120 protein during HIV infection of CD4 positive cells, and is required for HIV infection of lymphocytes and monocytes. Some studies have shown it to be available for HIV infection on the surface of the cell clustered around the CD4 protein. Yet conflicting studies have shown that it is not available on the cell surface, but instead is found in significant amounts in the blood plasma.
Assays used for PDI activity
Insulin Turbidity Assay: PDI breaks the two disulfide bonds between two insulin (a and b) chains that results in precipitation of b chain. This precipitation can be monitored at 620 nm, which is indirectly used to monitor PDI activity. Sensitivity of this assay is in micromolar range.
Di-E-GSSG assay: This is the fluorometric assay that can detect picomolar quantities of PDI and therefore is the most sensitive assay to date for detecting PDI activity. Di-E-GSSG has two eosin molecules attached to oxidized glutathione (GSSG). The proximity of eosin molecules leads to the quenching of its fluorescence. However, upon breakage of disulfide bond by PDI, fluorescence increases 70-fold.
- Wilkinson B, Gilbert HF (June 2004). "Protein disulfide isomerase". Biochimica et Biophysica Acta 1699 (1-2): 35–44. doi:10.1016/j.bbapap.2004.02.017. PMID 15158710.
- Gruber CW, Cemazar M, Heras B, Martin JL, Craik DJ (August 2006). "Protein disulfide isomerase: the structure of oxidative folding". Trends in Biochemical Sciences 31 (8): 455–64. doi:10.1016/j.tibs.2006.06.001. PMID 16815710.
- Hatahet F, Ruddock LW (October 2007). "Substrate recognition by the protein disulfide isomerases". FEBS J. 274 (20): 5223–34. doi:10.1111/j.1742-4658.2007.06058.x. PMID 17892489.
- Hatahet F, Ruddock LW (November 2009). "Protein Disulfide Isomerase: A Critical Evaluation of Its Function in Disulfide Bond Formation". Antioxidants & Redox Signaling. 11 (11): 2807–50. doi:10.1089/ars.2009.2466.x. PMID 19476414.
- Wittenberg G, Danon A (2008). "Disulfide bond formation in chloroplasts". Plant Science 175 (4): 459–466. doi:10.1016/j.plantsci.2008.05.011.
- Ryser, Hugues J.-P.; Flückiger, Rudolf (August 2005). "Progress in targeting HIV-1 entry". Drug Discovery Today. Keynote review 10 (16) (Elsevier). pp. 1085–1094. doi:10.1016/S1359-6446(05)03550-6. ISSN 1359-6446.
- Lundström J, Holmgren A (1990). "Protein disulfide-isomerase is a substrate for thioredoxin reductase and has thioredoxin-like activity". J. Biol. Chem. 265 (16): 9114–20. PMID 2188973.
- Lyles MM, Gilbert HF (1991). "Catalysis of the oxidative folding of ribonuclease A by protein disulfide isomerase: dependence of the rate on the composition of the redox buffer". Biochemistry 30 (3): 613–9. doi:10.1021/bi00217a004. PMID 1988050.
- Raturi A, Mutus B (2007). "Characterization of redox state and reductase activity of protein disulfide isomerase under different redox environments using a sensitive fluorescent assay". Free Radic. Biol. Med. 43 (1): 62–70. doi:10.1016/j.freeradbiomed.2007.03.025. PMID 17561094.
- Ellgaard L, Ruddock LW (January 2005). "The human protein disulphide isomerase family: substrate interactions and functional properties". EMBO Reports 6 (1): 28–32. doi:10.1038/sj.embor.7400311. PMC 1299221. PMID 15643448.
- Appenzeller-Herzog C, Ellgaard L (April 2008). "The human PDI family: versatility packed into a single fold". Biochimica et Biophysica Acta 1783 (4): 535–48. doi:10.1016/j.bbamcr.2007.11.010. PMID 18093543.
- Galligan JJ, Petersen DR (July 2012). "The human protein disulphide isomerase gene family". Human Genomics 6 (6). doi:10.1186/1479-7364-6-6.