Thioredoxin is a class of small redoxproteins 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 TXN2genes.[1][2]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.[3]
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.[6]
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 benefit of thioredoxins to reduce oxidative stress is shown by transgenic mice that overexpress thioredoxin, are more resistant to inflammation, and live 35% longer[9] — 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.[10]
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.[3]
Mechanism of action
The primary function of Thioredoxin (Trx) is the reduction of oxidized cysteine residues and the cleavage of disulfide bonds.[11] 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.[12] 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.[12]
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.[21]
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.[22]
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).[23][24] 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,[25] into the nucleus.[26] Once in the nucleus, reduced HDAC4 downregulates the activity of transcription factors such as NFAT that mediate cardiac hypertrophy.[12] Trx 1 also controls microRNA levels in the heart and has been found to inhibit cardiac hypertrophy by upregulating miR-98/let-7.[27]
See also
RuBisCO - enzyme activity regulated by thioredoxin
Peroxiredoxin - enzyme activity regulated by thioredoxin
↑Wollman EE, d'Auriol L, Rimsky L, Shaw A, Jacquot JP, Wingfield P, Graber P, Dessarps F, Robin P, Galibert F (October 1988). "Cloning and expression of a cDNA for human thioredoxin". The Journal of Biological Chemistry. 263 (30): 15506–12. PMID3170595.
↑Arnér ES, Holmgren A (October 2000). "Physiological functions of thioredoxin and thioredoxin reductase". European Journal of Biochemistry. 267 (20): 6102–9. doi:10.1046/j.1432-1327.2000.01701.x. PMID11012661.
↑Yoshida T, Nakamura H, Masutani H, Yodoi J (December 2005). "The involvement of thioredoxin and thioredoxin binding protein-2 on cellular proliferation and aging process". Annals of the New York Academy of Sciences. 1055: 1–12. doi:10.1196/annals.1323.002. PMID16387713.
↑Muller, F.L., Lustgarten, M.S., Jang, Y., Richardson, A. & Van Remmen, H. Trends in oxidative aging theories. Free Radic Biol Med 43, 477-503 (2007).
↑Liu Y, Min W (June 2002). "Thioredoxin promotes ASK1 ubiquitination and degradation to inhibit ASK1-mediated apoptosis in a redox activity-independent manner". Circulation Research. 90 (12): 1259–66. doi:10.1161/01.res.0000022160.64355.62. PMID12089063.
↑Matsumoto K, Masutani H, Nishiyama A, Hashimoto S, Gon Y, Horie T, Yodoi J (July 2002). "C-propeptide region of human pro alpha 1 type 1 collagen interacts with thioredoxin". Biochemical and Biophysical Research Communications. 295 (3): 663–7. doi:10.1016/s0006-291x(02)00727-1. PMID12099690.
↑Makino Y, Yoshikawa N, Okamoto K, Hirota K, Yodoi J, Makino I, Tanaka H (January 1999). "Direct association with thioredoxin allows redox regulation of glucocorticoid receptor function". The Journal of Biological Chemistry. 274 (5): 3182–8. doi:10.1074/jbc.274.5.3182. PMID9915858.
↑Li X, Luo Y, Yu L, Lin Y, Luo D, Zhang H, He Y, Kim YO, Kim Y, Tang S, Min W (April 2008). "SENP1 mediates TNF-induced desumoylation and cytoplasmic translocation of HIPK1 to enhance ASK1-dependent apoptosis". Cell Death and Differentiation. 15 (4): 739–50. doi:10.1038/sj.cdd.4402303. PMID18219322.
↑Nishiyama A, Matsui M, Iwata S, Hirota K, Masutani H, Nakamura H, Takagi Y, Sono H, Gon Y, Yodoi J (July 1999). "Identification of thioredoxin-binding protein-2/vitamin D(3) up-regulated protein 1 as a negative regulator of thioredoxin function and expression". The Journal of Biological Chemistry. 274 (31): 21645–50. doi:10.1074/jbc.274.31.21645. PMID10419473.
↑Ago T, Yeh I, Yamamoto M, Schinke-Braun M, Brown JA, Tian B, Sadoshima J (2006). "Thioredoxin1 upregulates mitochondrial proteins related to oxidative phosphorylation and TCA cycle in the heart". Antioxidants & Redox Signaling. 8 (9–10): 1635–50. doi:10.1089/ars.2006.8.1635. PMID16987018.
↑Ago T, Liu T, Zhai P, Chen W, Li H, Molkentin JD, Vatner SF, Sadoshima J (June 2008). "A redox-dependent pathway for regulating class II HDACs and cardiac hypertrophy". Cell. 133 (6): 978–93. doi:10.1016/j.cell.2008.04.041. PMID18555775.
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Nishinaka Y, Masutani H, Nakamura H, Yodoi J (2002). "Regulatory roles of thioredoxin in oxidative stress-induced cellular responses". Redox Report. 6 (5): 289–95. doi:10.1179/135100001101536427. PMID11778846.
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1cqg: HIGH RESOLUTION SOLUTION NMR STRUCTURE OF MIXED DISULFIDE INTERMEDIATE BETWEEN HUMAN THIOREDOXIN (C35A, C62A, C69A, C73A) MUTANT AND A 13 RESIDUE PEPTIDE COMPRISING ITS TARGET SITE IN HUMAN REF-1 (RESIDUES 59-71 OF THE P50 SUBUNIT OF NFKB), NMR, 31 STRUCTURES
1cqh: HIGH RESOLUTION SOLUTION NMR STRUCTURE OF MIXED DISULFIDE INTERMEDIATE BETWEEN HUMAN THIOREDOXIN (C35A, C62A, C69A, C73A) MUTANT AND A 13 RESIDUE PEPTIDE COMPRISING ITS TARGET SITE IN HUMAN REF-1 (RESIDUES 59-71 OF THE P50 SUBUNIT OF NFKB), NMR, MINIMIZED AVERAGE STRUCTURE
1mdi: HIGH RESOLUTION SOLUTION NMR STRUCTURE OF MIXED DISULFIDE INTERMEDIATE BETWEEN MUTANT HUMAN THIOREDOXIN AND A 13 RESIDUE PEPTIDE COMPRISING ITS TARGET SITE IN HUMAN NFKB
1mdj: HIGH RESOLUTION SOLUTION NMR STRUCTURE OF MIXED DISULFIDE INTERMEDIATE BETWEEN HUMAN THIOREDOXIN (C35A, C62A, C69A, C73A) MUTANT AND A 13 RESIDUE PEPTIDE COMPRISING ITS TARGET SITE IN HUMAN NFKB (RESIDUES 56-68 OF THE P50 SUBUNIT OF NFKB)
1mdk: HIGH RESOLUTION SOLUTION NMR STRUCTURE OF MIXED DISULFIDE INTERMEDIATE BETWEEN HUMAN THIOREDOXIN (C35A, C62A, C69A, C73A) MUTANT AND A 13 RESIDUE PEPTIDE COMPRISING ITS TARGET SITE IN HUMAN NFKB (RESIDUES 56-68 OF THE P50 SUBUNIT OF NFKB)