Thioredoxin

TXN
Available structures PDB Ortholog search: PDBe RCSB showList of PDB id codes 4TRX, 1AIU, 1AUC, 1CQG, 1CQH, 1ERT, 1ERU, 1ERV, 1ERW, 1MDI, 1MDJ, 1MDK, 1TRS, 1TRU, 1TRV, 1TRW, 2HSH, 2HXK, 2IFQ, 2IIY, 3E3E, 3KD0, 3M9J, 3M9K, 3QFA, 3QFB, 3TRX, 4LL1, 4LL4, 4OO4, 4OO5, 4POK, 4POL, 4POM, 4PUF, 5DQY
Identifiers
Aliases	TXN, TRDX, TRX, TRX1, thioredoxin, Trx80
External IDs	OMIM: 187700 MGI: 98874 HomoloGene: 128202 GeneCards: TXN
showGene location (Human) Chr. Chromosome 9 (human)[1] Band 9q31.3 Start 110,243,810 bp[1] End 110,256,507 bp[1]
showGene location (Mouse) Chr. Chromosome 4 (mouse)[2] Band 4 B3|4 31.87 cM Start 57,943,373 bp[2] End 57,956,411 bp[2]
showRNA expression pattern More reference expression data
showGene ontology Molecular function • protein-disulfide reductase activity • oxidoreductase activity, acting on a sulfur group of donors, disulfide as acceptor • GO:0001948 protein binding • thioredoxin-disulfide reductase activity • protein-disulfide reductase (NAD(P)) activity • RNA binding Cellular component • extracellular region • extracellular exosome • nucleus • cytoplasm • mitochondrion • cytosol • nucleoplasm Biological process • activation of protein kinase B activity • positive regulation of protein kinase B signaling • movement of cell or subcellular component • nucleobase-containing small molecule interconversion • glycerol ether metabolic process • regulation of transcription, DNA-templated • cell-cell signaling • negative regulation of transcription by RNA polymerase II • cell redox homeostasis • transcription, DNA-templated • positive regulation of peptidyl-serine phosphorylation • negative regulation of protein export from nucleus • response to radiation • positive regulation of DNA binding • negative regulation of hydrogen peroxide-induced cell death • cell population proliferation • signal transduction • protein repair • cellular oxidant detoxification • cellular response to oxidative stress Sources:Amigo / QuickGO
Orthologs
Species	Human	Mouse
Entrez	7295	22166
Ensembl	ENSG00000136810	ENSMUSG00000028367
UniProt	P10599	P10639
RefSeq (mRNA)	NM_003329 NM_001244938	NM_011660
RefSeq (protein)	NP_001231867 NP_003320	NP_035790
Location (UCSC)	Chr 9: 110.24 – 110.26 Mb	Chr 4: 57.94 – 57.96 Mb
PubMed search	[3]	[4]
Wikidata
View/Edit Human View/Edit Mouse

Thioredoxin is a class of small redox proteins known to be present in all organisms. It plays a role in many important biological processes, including redox signaling. In humans, thioredoxins are encoded by TXN and TXN2 genes.^[5][6] Loss-of-function mutation of either of the two human thioredoxin genes is lethal at the four-cell stage of the developing embryo. Although not entirely understood, thioredoxin plays a central role in humans and is increasingly linked to medicine through their response to reactive oxygen species (ROS). In plants, thioredoxins regulate a spectrum of critical functions, ranging from photosynthesis to growth, flowering and the development and germination of seeds. They have also recently been found to play a role in cell-to-cell communication.^[7]

Function[]

Thioredoxins are proteins that act as antioxidants by facilitating the reduction of other proteins by cysteine thiol-disulfide exchange. Thioredoxins are found in nearly all known organisms and are essential for life in mammals.^[8][9]

Thioredoxin is a 12-kD oxidoreductase enzyme containing a dithiol-disulfide active site. It is ubiquitous and found in many organisms from plants and bacteria to mammals. Multiple in vitro substrates for thioredoxin have been identified, including ribonuclease, choriogonadotropins, coagulation factors, glucocorticoid receptor, and insulin. Reduction of insulin is classically used as an activity test.^[10]

Thioredoxins are characterized at the level of their amino acid sequence by the presence of two vicinal cysteines in a CXXC motif. These two cysteines are the key to the ability of thioredoxin to reduce other proteins. Thioredoxin proteins also have a characteristic tertiary structure termed the thioredoxin fold.

The thioredoxins are kept in the reduced state by the thioredoxin reductase, in a NADPH-dependent reaction.^[11] Thioredoxins act as electron donors to peroxidases and ribonucleotide reductase.^[12] The related glutaredoxins share many of the functions of thioredoxins, but are reduced by glutathione rather than a specific reductase.

The benefit of thioredoxins to reduce oxidative stress is shown by transgenic mice that overexpress thioredoxin, are more resistant to inflammation, and live 35% longer^[13] — supporting the free radical theory of aging. However, the controls of this study were short lived, which may have contributed to the apparent increase in longevity.^[14] Trx1 can regulate non-redox post-translational modifications.^[15] In the mice with cardiac-specific overexpression of Trx1, the proteomics study found that SET and MYND domain-containing protein 1 (SMYD1), a lysine methyltransferase highly expressed in cardiac and other muscle tissues, is also upregulated. This suggests that Trx1 may also play an role in protein methylation via regulating SMYD1 expression, which is independent of its oxidoreductase activity.^[15]

Plants have an unusually complex complement of Trxs composed of six well-defined types (Trxs f, m, x, y, h, and o) that reside in different cell compartments and function in an array of processes. In 2010 it was discovered for the first time that thioredoxin proteins are able to move from cell to cell, representing a novel form of cellular communication in plants.^[7]

Mechanism of action[]

The primary function of Thioredoxin (Trx) is the reduction of oxidized cysteine residues and the cleavage of disulfide bonds.^[16] For Trx1, this process begins by attack of Cys32, one of the residues conserved in the thioredoxin CXXC motif, onto the oxidized group of the substrate.^[17] Almost immediately after this event Cys35, the other conserved Cys residue in Trx1, forms a disulfide bond with Cys32, thereby transferring 2 electrons to the substrate which is now in its reduced form. Oxidized Trx1 is then reduced by thioredoxin reductase, which in turn is reduced by NADPH as described above.^[17]

Mechanism of Trx1 reducing a substrate

Interactions[]

Thioredoxin has been shown to interact with:

• ASK1,^[18][19][20]
• Collagen, type I, alpha 1,^[21]
• Glucocorticoid receptor,^[22]
• SENP1,^[23]
• TXNIP.^[24]
• NF-κB – by reducing a disulfide bond in NF-κB, Trx1 promotes binding of this transcription factor to DNA.^[25]
• AP1 via Ref1 – Trx1 indirectly increases the DNA-binding activity of activator protein 1 (AP1) by reducing the DNA repair enzyme redox factor 1 (Ref-1), which in turn reduces AP1 in an example of a redox regulation cascade.^[26]
• AMPK – AMPK function in cardiomyocytes is preserved during oxidative stress due to an interaction between AMPK and Trx1. By forming a disulfide bridge between the two proteins, Trx1 prevents the formation and aggregation of oxidized AMPK, thereby allowing AMPK to function normally and participate in signaling cascades.^[27]

Effect on cardiac hypertrophy[]

Trx1 has been shown to downregulate cardiac hypertrophy, the thickening of the walls of the lower heart chambers, by interactions with several different targets. Trx1 upregulates the transcriptional activity of nuclear respiratory factors 1 and 2 (NRF1 and NRF2) and stimulates the expression of peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α).^[28][29] Furthermore, Trx1 reduces two cysteine residues in histone deacetylase 4 (HDAC4), which allows HDAC4 to be imported from the cytosol, where the oxidized form resides,^[30] into the nucleus.^[31] Once in the nucleus, reduced HDAC4 downregulates the activity of transcription factors such as NFAT that mediate cardiac hypertrophy.^[17] Trx 1 also controls microRNA levels in the heart and has been found to inhibit cardiac hypertrophy by upregulating miR-98/let-7.^[32] Trx1 can regulate the expression level of SMYD1, thus may indirectly modulate protein methylation for purpose of cardiac protection.^[15]

Thioredoxin in skin care[]

Thioredoxin is used in skin care products as an antioxidant in conjunction with glutaredoxin and glutathione.^{[citation needed]}

See also[]

• RuBisCO - enzyme activity regulated by thioredoxin
• Peroxiredoxin - enzyme activity regulated by thioredoxin
• Thioredoxin fold
• Thioredoxin reductase

References[]

Further reading[]

External links[]

• Thioredoxin at the US National Library of Medicine Medical Subject Headings (MeSH)
• Overview of all the structural information available in the PDB for UniProt: P10599 (Thioredoxin) at the PDBe-KB.