TXN
Available structures PDB Ortholog search: PDBe RCSB List 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
Gene location (Human) Chr. Chromosome 9 (human)[1] Band 9q31.3 Start 110,243,810 bp[1] End 110,256,507 bp[1]
Gene 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]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in cavity of mouth human penis body of tongue jejunal mucosa right uterine tube rectum islet of Langerhans stromal cell of endometrium epithelium of esophagus trachea Top expressed in jejunum ileum colon duodenum proximal tubule synovial joint thymus esophagus ankle joint yolk sac More reference expression data BioGPS More reference expression data
Gene ontology Molecular function protein-disulfide reductase activity oxidoreductase activity, acting on a sulfur group of donors, disulfide as acceptor 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 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 (TRX or TXN) 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 is 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. Thioredoxins play a role in cell-to-cell communication.^[7]

Occurrence

They are found in nearly all known organisms and are essential for life in mammals.^[8][9]

Function

The primary function of thioredoxin (Trx) is the reduction of oxidized cysteine residues and the cleavage of disulfide bonds.^[10] 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.^[11] The thioredoxins are maintained in their reduced state by the flavoenzyme thioredoxin reductase, in a NADPH-dependent reaction.^[12] Thioredoxins act as electron donors to peroxidases and ribonucleotide reductase.^[13] The related glutaredoxins share many of the functions of thioredoxins, but are reduced by glutathione rather than a specific reductase.

Structure and mechanism

Thioredoxin is a 12-kD oxidoreductase protein. Thioredoxin proteins also have a characteristic tertiary structure termed the thioredoxin fold. The active site contains a dithiols in a CXXC motif. These two cysteines are the key to the ability of thioredoxin to reduce other proteins.

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.^[14] 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.^[14]

Mechanism of Trx1 reducing a substrate

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 Trx's composed of six well-defined types (Trxs f, m, x, y, h, and o) that reside in diverse cell compartments and function in an array of processes. Thioredoxin proteins move from cell to cell, representing a novel form of cellular communication in plants.^[7]

Interactions

Thioredoxin has been shown to interact with:

• ASK1,^[16][17][18]
• Collagen, type I, alpha 1,^[19]
• Glucocorticoid receptor,^[20]
• SENP1,^[21]
• TXNIP.^[22]
• NF-κB – by reducing a disulfide bond in NF-κB, Trx1 promotes binding of this transcription factor to DNA.^[23]
• 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.^[24]
• 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.^[25]

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).^[26][27] 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,^[28] into the nucleus.^[29] Once in the nucleus, reduced HDAC4 downregulates the activity of transcription factors such as NFAT that mediate cardiac hypertrophy.^[14] Trx 1 also controls microRNA levels in the heart and has been found to inhibit cardiac hypertrophy by upregulating miR-98/let-7.^[30] 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.

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 U.S. 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.