Protein disulfide isomerase

protein
Name = protein disulfide isomerase family A, member 2
caption =


width =
HGNCid = 14180
Symbol = PDIA2
AltSymbols = PDIP
EntrezGene = 64714
OMIM = 608012
RefSeq = NM_006849
UniProt = Q13087
PDB =
ECnumber =
Chromosome = 16
Arm = p
Band = 13.3
LocusSupplementaryData = protein
Name = protein disulfide isomerase family A, member 3
caption =


width =
HGNCid = 4606
Symbol = PDIA3
AltSymbols = GRP58
EntrezGene = 2923
OMIM = 602046
RefSeq = NM_005313
UniProt = P30101
PDB =
ECnumber =
Chromosome = 15
Arm = q
Band = 15
LocusSupplementaryData = protein
Name = protein disulfide isomerase family A, member 4
caption =


width =
HGNCid = 30167
Symbol = PDIA4
AltSymbols =
EntrezGene = 9601
OMIM =
RefSeq = NM_004911
UniProt = P13667
PDB =
ECnumber =
Chromosome = 7
Arm = q
Band = 35
LocusSupplementaryData = protein
Name = protein disulfide isomerase family A, member 5
caption =


width =
HGNCid = 24811
Symbol = PDIA5
AltSymbols =
EntrezGene = 10954
OMIM =
RefSeq = NM_006810
UniProt = Q14554
PDB =
ECnumber = 5.3.4.1
Chromosome = 3
Arm = q
Band = 21.1
LocusSupplementaryData = protein
Name = protein disulfide isomerase family A, member 6
caption =


width =
HGNCid = 30168
Symbol = PDIA6
AltSymbols = TXNDC7
EntrezGene = 10130
OMIM =
RefSeq = NM_005742
UniProt = Q15084
PDB =
ECnumber =
Chromosome = 2
Arm = p
Band = 25.1
LocusSupplementaryData =

Protein disulfide isomerase or PDI (EC number|5.3.4.1) is an enzyme in the endoplasmic reticulum in eukaryotes or periplasmic space of prokaryotescite journal | author = Gleiter S, Bardwell JC | title = Disulfide bond isomerization in prokaryotes | journal = Biochimica et biophysica acta | volume = 1783 | issue = 4 | pages = 530–4 | year = 2008 | month = April | pmid = 18342631 | pmc = 2391271 | doi = 10.1016/j.bbamcr.2008.02.009 | url = ] that catalyzes the formation and breakage of disulfide bonds between cysteine residues within proteins as they fold.cite journal | author = Wilkinson B, Gilbert HF | title = Protein disulfide isomerase | journal = Biochimica et biophysica acta | volume = 1699 | issue = 1-2 | pages = 35–44 | year = 2004 | month = June | pmid = 15158710 | doi = 10.1016/j.bbapap.2004.02.017 | url = ] cite journal | author = Gruber CW, Cemazar M, Heras B, Martin JL, Craik DJ | title = Protein disulfide isomerase: the structure of oxidative folding | journal = Trends in biochemical sciences | volume = 31 | issue = 8 | pages = 455–64 | year = 2006 | month = August | pmid = 16815710 | doi = 10.1016/j.tibs.2006.06.001 | url = ] 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.

Function

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.

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.

Redox signaling

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 photoisystem II core protein D1. PDI has also been suggested to play a role in the formation of regulatory disulfide bonds in chloroplasts.cite journal | author =Wittenberg G, Danon A | title = Disulfide bond formation in chloroplasts | journal = Plant Science | volume = 175 | issue = 4 | pages = 459–466 | year = 2008| doi = 10.1016/j.plantsci.2008.05.011 | url = ]

Other functions

PDI 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.

PDI has been found to be involved in the breaking of bonds on the HIV gp120 protein during HIV infection ofCD4 positive cells, and is required for HIV infection of lymphocytes and monoctyes. 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 monitor PDI activity. [cite journal |author=Lundström J, Holmgren A |title=Protein disulfide-isomerase is a substrate for thioredoxin reductase and has thioredoxin-like activity |journal=J. Biol. Chem. |volume=265 |issue=16 |pages=9114–20 |year=1990 |pmid=2188973] Sensitivity of this assay is in micromolar range.

"ScRNase assay": PDI converts scrambled (inactive) RNase into native (active) RNase that further acts on its substrate. [cite journal |author=Lyles MM, Gilbert HF |title=Catalysis of the oxidative folding of ribonuclease A by protein disulfide isomerase: dependence of the rate on the composition of the redox buffer |journal=Biochemistry |volume=30 |issue=3 |pages=613–9 |year=1991 |pmid=1988050 |doi=10.1021/bi00217a004] The sensitivty 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. [cite journal |author=Raturi A, Mutus B |title=Characterization of redox state and reductase activity of protein disulfide isomerase under different redox environments using a sensitive fluorescent assay |journal=Free Radic. Biol. Med. |volume=43 |issue=1 |pages=62–70 |year=2007 |pmid=17561094 |doi=10.1016/j.freeradbiomed.2007.03.025] 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.

Members

Human genes encoding Protein disulfide isomerases include:cite journal | author = Ellgaard L, Ruddock LW | title = The human protein disulphide isomerase family: substrate interactions and functional properties | journal = EMBO reports | volume = 6 | issue = 1 | pages = 28–32 | year = 2005 | month = January | pmid = 15643448 | pmc = 1299221 | doi = 10.1038/sj.embor.7400311 | url = ] cite journal | author = Appenzeller-Herzog C, Ellgaard L | title = The human PDI family: versatility packed into a single fold | journal = Biochimica et biophysica acta | volume = 1783 | issue = 4 | pages = 535–48 | year = 2008 | month = April | pmid = 18093543 | doi = 10.1016/j.bbamcr.2007.11.010 | url = ]
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References

External links

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