Protein disulfide-isomerase explained

Interpro:IPR005792
Protein disulfide-isomerase
Ec Number:5.3.4.1
Cas Number:37318-49-3
Go Code:0003756
protein disulfide isomerase family A, member 2
Hgncid:14180
Symbol:PDIA2
Altsymbols:PDIP
Entrezgene:64714
Omim:608012
Refseq:NM_006849
Uniprot:Q13087
Chromosome:16
Arm:p
Band:13.3
protein disulfide isomerase family A, member 3
Hgncid:4606
Symbol:PDIA3
Altsymbols:GRP58
Entrezgene:2923
Omim:602046
Refseq:NM_005313
Uniprot:P30101
Chromosome:15
Arm:q
Band:15
protein disulfide isomerase family A, member 4
Hgncid:30167
Symbol:PDIA4
Entrezgene:9601
Refseq:NM_004911
Uniprot:P13667
Chromosome:7
Arm:q
Band:35
protein disulfide isomerase family A, member 5
Hgncid:24811
Symbol:PDIA5
Entrezgene:10954
Refseq:NM_006810
Uniprot:Q14554
Ecnumber:5.3.4.1
Chromosome:3
Arm:q
Band:21.1
protein disulfide isomerase family A, member 6
Hgncid:30168
Symbol:PDIA6
Altsymbols:TXNDC7
Entrezgene:10130
Refseq:NM_005742
Uniprot:Q15084
Chromosome:2
Arm:p
Band:25.1

Protein disulfide isomerase, or PDI, is an enzyme in the endoplasmic reticulum (ER) in eukaryotes and the periplasm of bacteria that catalyzes the formation and breakage of disulfide bonds between cysteine residues within proteins as they fold.[1] [2] [3] 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.

Structure

Protein disulfide-isomerase has two catalytic thioredoxin-like domains (active sites), each containing the canonical CGHC motif, and two non catalytic domains.[4] [5] [6] This structure is similar to the structure of enzymes responsible for oxidative folding in the intermembrane space of the mitochondria; an example of this is mitochondrial IMS import and assembly (Mia40), which has 2 catalytic domains that contain a CX9C, which is similar to the CGHC domain of PDI.[7] Bacterial DsbA, responsible for oxidative folding, also has a thioredoxin CXXC domain.[8]

Function

Protein folding

PDI displays oxidoreductase and isomerase properties, both of which depend on the type of substrate that binds to protein disulfide-isomerase and changes in protein disulfide-isomerase's redox state. These types of activities allow for oxidative folding of proteins. Oxidative folding involves the oxidation of reduced cysteine residues of nascent proteins; upon oxidation of these cysteine residues, disulfide bridges are formed, which stabilizes proteins and allows for native structures (namely tertiary and quaternary structures).

Regular oxidative folding mechanism and pathway

PDI is specifically responsible for folding proteins in the ER. In an unfolded protein, a cysteine residue forms a mixed disulfide with a cysteine residue in an active site (CGHC motif) of protein disulfide-isomerase. A second cysteine residue then forms a stable disulfide bridge within the substrate, leaving protein disulfide-isomerase's two active-site cysteine residues in a reduced state.

Afterwards, PDI can be regenerated to its oxidized form in the endoplasmic reticulum by transferring electrons to reoxidizing proteins such ER oxidoreductin 1 (Ero 1), VKOR (vitamin K epoxide reductase), glutathione peroxidase (Gpx7/8), and PrxIV (peroxiredoxin IV).[9] [10] Ero1 is thought to be the main reoxidizing protein of PDI, and the pathway of reoxidation of PDI for Ero1 is more understood than that of other proteins. Ero1 accepts electrons from PDI and donates these electrons to oxygen molecules in the ER, which leads to the formation of hydrogen peroxide.

Misfolded protein mechanism

The reduced (dithiol) form of protein disulfide-isomerase is able to catalyze a reduction of a misformed disulfide bridge of a substrate through either reductase activity or isomerase activity.[11] For the reductase method, a misfolded substrate disulfide bond is converted to a pair of reduced cysteine residues by the transfer of electrons from glutathione and NADPH. Afterwards, normal folding occurs with oxidative disulfide bond formation between the correct pairs of substrate cysteine residues, leading to a properly folded protein. For the isomerase method, intramolecular rearrangement of substrate functional groups is catalyzed near the N terminus of each active site. Therefore, protein disulfide-isomerase is capable of catalyzing the post-translational modification disulfide exchange.

Redox signaling

In the chloroplasts of the unicellular algae Chlamydomonas reinhardtii the protein disulfide-isomerase RB60 serves as a redox sensor component of an mRNA-binding protein complex implicated in the photoregulation of the translation of psbA, the RNA encoding for the photosystem II core protein D1. Protein disulfide-isomerase has also been suggested to play a role in the formation of regulatory disulfide bonds in chloroplasts.[12]

Other functions

Immune system

Protein disulfide-isomerase helps load antigenic peptides into MHC class I molecules. These molecules (MHC I) are related to the peptide presentation by antigen-presenting cells in the immune response.

Protein disulfide-isomerase 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.[13] 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.

Chaperone activity

Another major function of protein disulfide-isomerase relates to its activity as a chaperone; its b' domain aids in the binding of misfolded protein for subsequent degradation. This is regulated by three ER membrane proteins, Protein Kinase RNA-like endoplasmic reticulum kinase (PERK), inositol-requiring kinase 1 (IRE1), and activating transcription factor 6 (ATF6).[14] They respond to high levels of misfolded proteins in the ER through intracellular signaling cascades that can activate PDI's chaperone activity. These signals can also inactivate translation of these misfolded proteins, because the cascade travels from the ER to the nucleus.

Activity assays

Insulin turbidity assay: protein disulfide-isomerase 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 650 nm, which is indirectly used to monitor protein disulfide-isomerase activity.[15] Sensitivity of this assay is in micromolar range.

ScRNase assay: protein disulfide-isomerase converts scrambled (inactive) RNase into native (active) RNase that further acts on its substrate.[16] The sensitivity is in micromolar range.

Di-E-GSSG assay: This is the fluorometric assay that can detect picomolar quantities of protein disulfide-isomerase and therefore is the most sensitive assay to date for detecting protein disulfide-isomerase activity.[17] 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 protein disulfide-isomerase, fluorescence increases 70-fold.

Stress and inhibition

Effects of nitrosative stress

Redox dysregulation leads to increases in nitrosative stress in the endoplasmic reticulum. Such adverse changes in the normal cellular environment of susceptible cells, such as neurons, leads to nonfunctioning thiol-containing enzymes. More specifically, protein disulfide-isomerase can no longer fix misfolded proteins once its thiol group in its active site has a nitric monoxide group attached to it; as a result, accumulation of misfolded proteins occurs in neurons, which has been associated with the development of neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease.

Inhibition

Due to the role of protein disulfide-isomerase in a number of disease states, small molecule inhibitors of protein disulfide-isomerase have been developed. These molecules can either target the active site of protein disulfide-isomerase irreversibly[18] or reversibly.[19]

It has been shown that protein disulfide-isomerase activity is inhibited by red wine and grape juice, which could be the explanation for the French paradox.[20]

Members

Human genes encoding protein disulfide isomerases include:[3] [21] [22]

Notes and References

  1. Wilkinson B, Gilbert HF . Protein disulfide isomerase . Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics . 1699 . 1–2 . 35–44 . June 2004 . 15158710 . 10.1016/j.bbapap.2004.02.017 .
  2. Gruber CW, Cemazar M, Heras B, Martin JL, Craik DJ . Protein disulfide isomerase: the structure of oxidative folding . Trends in Biochemical Sciences . 31 . 8 . 455–64 . August 2006 . 16815710 . 10.1016/j.tibs.2006.06.001 .
  3. Galligan JJ, Petersen DR . The human protein disulfide isomerase gene family . Human Genomics . 6 . 1 . 6 . July 2012 . 23245351 . 3500226 . 10.1186/1479-7364-6-6 . free .
  4. Perri ER, Thomas CJ, Parakh S, Spencer DM, Atkin JD . The Unfolded Protein Response and the Role of Protein Disulfide Isomerase in Neurodegeneration . en . Frontiers in Cell and Developmental Biology . 3 . 80 . 2016 . 26779479 . 4705227 . 10.3389/fcell.2015.00080 . free .
  5. Bechtel TJ, Weerapana E . From structure to redox: The diverse functional roles of disulfides and implications in disease . Proteomics . 17 . 6 . March 2017 . 10.1002/pmic.201600391 . 28044432 . 5367942 . 10.1002/pmic.201600391 .
  6. Soares Moretti AI, Martins Laurindo FR . Protein disulfide isomerases: Redox connections in and out of the endoplasmic reticulum . Archives of Biochemistry and Biophysics . 617 . 106–119 . March 2017 . 27889386 . 10.1016/j.abb.2016.11.007 . The Chemistry of Redox Signaling .
  7. Erdogan AJ, Riemer J . Mitochondrial disulfide relay and its substrates: mechanisms in health and disease . Cell and Tissue Research . 367 . 1 . 59–72 . January 2017 . 27543052 . 10.1007/s00441-016-2481-z . 35346837 .
  8. Hu SH, Peek JA, Rattigan E, Taylor RK, Martin JL . Structure of TcpG, the DsbA protein folding catalyst from Vibrio cholerae . Journal of Molecular Biology . 268 . 1 . 137–46 . April 1997 . 9149147 . 10.1006/jmbi.1997.0940 . free .
  9. Manganas P, MacPherson L, Tokatlidis K . Oxidative protein biogenesis and redox regulation in the mitochondrial intermembrane space . Cell and Tissue Research . 367 . 1 . 43–57 . January 2017 . 27632163 . 5203823 . 10.1007/s00441-016-2488-5 .
  10. Oka OB, Yeoh HY, Bulleid NJ . Thiol-disulfide exchange between the PDI family of oxidoreductases negates the requirement for an oxidase or reductase for each enzyme . The Biochemical Journal . 469 . 2 . 279–88 . July 2015 . 25989104 . 4613490 . 10.1042/bj20141423 .
  11. Hatahet F, Ruddock LW . Substrate recognition by the protein disulfide isomerases . The FEBS Journal . 274 . 20 . 5223–34 . October 2007 . 17892489 . 10.1111/j.1742-4658.2007.06058.x . 9455925 .
  12. Wittenberg G, Danon A . Disulfide bond formation in chloroplasts . Plant Science . 175 . 4 . 459–466 . 2008. 10.1016/j.plantsci.2008.05.011 .
  13. Ryser HJ, Flückiger R . Progress in targeting HIV-1 entry . Drug Discovery Today . 10 . 16 . 1085–94 . August 2005 . 16182193 . 10.1016/S1359-6446(05)03550-6 .
  14. McBean GJ, López MG, Wallner FK . Redox-based therapeutics in neurodegenerative disease . British Journal of Pharmacology . 174 . 12 . 1750–1770 . June 2017 . 27477685 . 5446580 . 10.1111/bph.13551 .
  15. Lundström J, Holmgren A . Protein disulfide-isomerase is a substrate for thioredoxin reductase and has thioredoxin-like activity . The Journal of Biological Chemistry . 265 . 16 . 9114–20 . June 1990 . 10.1016/S0021-9258(19)38819-2 . 2188973 . free .
  16. Lyles MM, Gilbert HF . 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 . January 1991 . 1988050 . 10.1021/bi00217a004 .
  17. Raturi A, Mutus B . Characterization of redox state and reductase activity of protein disulfide isomerase under different redox environments using a sensitive fluorescent assay . Free Radical Biology & Medicine . 43 . 1 . 62–70 . July 2007 . 17561094 . 10.1016/j.freeradbiomed.2007.03.025 .
  18. Hoffstrom BG, Kaplan A, Letso R, Schmid RS, Turmel GJ, Lo DC, Stockwell BR . Inhibitors of protein disulfide isomerase suppress apoptosis induced by misfolded proteins . Nature Chemical Biology . 6 . 12 . 900–6 . December 2010 . 21079601 . 3018711 . 10.1038/nchembio.467 .
  19. Kaplan A, Gaschler MM, Dunn DE, Colligan R, Brown LM, Palmer AG, Lo DC, Stockwell BR . Small molecule-induced oxidation of protein disulfide isomerase is neuroprotective . Proceedings of the National Academy of Sciences of the United States of America . 112 . 17 . E2245-52 . April 2015 . 25848045 . 4418888 . 10.1073/pnas.1500439112 . 2015PNAS..112E2245K . free .
  20. Galinski CN, Zwicker JI, Kennedy DR . Revisiting the mechanistic basis of the French Paradox: Red wine inhibits the activity of protein disulfide isomerase in vitro . Thrombosis Research . 137 . 169–173 . January 2016 . 26585763 . 4706467 . 10.1016/j.thromres.2015.11.003 .
  21. Ellgaard L, Ruddock LW . The human protein disulphide isomerase family: substrate interactions and functional properties . EMBO Reports . 6 . 1 . 28–32 . January 2005 . 15643448 . 1299221 . 10.1038/sj.embor.7400311 .
  22. Appenzeller-Herzog C, Ellgaard L . The human PDI family: versatility packed into a single fold . Biochimica et Biophysica Acta (BBA) - Molecular Cell Research . 1783 . 4 . 535–48 . April 2008 . 18093543 . 10.1016/j.bbamcr.2007.11.010 . free .