Thioredoxin

Thioredoxin (TRX or TXN) is a class of small

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.

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]

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]

• 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]
• 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]

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.^{[citation needed]}

See also

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

References