Thioredoxin reductase
Thioredoxin reductase | |
---|---|
Identifiers | |
Symbol | ? |
SCOP2 | 1zof / SCOPe / SUPFAM |
Thioredoxin reductases (TR, TrxR) (
Cellular role
Thioredoxin reductases are enzymes that catalyze the reduction of thioredoxin[1] and hence they are a central component in the thioredoxin system. Together with thioredoxin (Trx) and NADPH this system's most general description is as a system for reducing disulfide bonds in cells. Electrons are taken from NADPH via TrxR and are transferred to the active site of Trx, which goes on to reduce protein disulfides or other substrates.[6] The Trx system exists in all living cells and has an evolutionary history tied to DNA as a genetic material, defense against oxidative damage due to oxygen metabolism, and redox signaling using molecules like hydrogen peroxide and nitric oxide.[7][8]
Diversity
Two classes of thioredoxin reductase have evolved independently:
- A high molecular weight (MW = ~55,000) type containing a mercuric reductase and lipoamide dehydrogenase.[5]
- A low molecular weight (MW = ~ 35,000) type has been identified in archaea, bacteria and other eukarya.[5]
These two classes of TrxR have only ~20% sequence identity in the section of primary sequence where they can be reliably aligned.[5] The net reaction of both classes of TrxR is identical but the mechanism of action of each is distinct.[9]
Humans express three thioredoxin reductase isozymes: thioredoxin reductase 1 (TrxR1, cytosolic), thioredoxin reductase 2 (TrxR2, mitochondrial), thioredoxin reductase 3 (TrxR3, testis specific).[10] Each isozyme is encoded by a separate gene:
|
|
|
Structure
E. coli
In E. coli ThxR there are two binding domains, one for
-
Structure of E. coli ThxR dimer bound thioredoxin
-
Structure of E. coli ThxR with FAD and NADPH prosthetic groups labeled
Mammalian
Mammalian TrxR structure is similar to E. coli. It contains a
-
Structure of human ThxR FAD and NADPH prosthetic groups
Mechanism
E. coli
In E. coli ThxR the spatial orientation of the FAD and NADPH domains are such that the redox-active rings of FAD and NADPH are not in close proximity to each other.[1] When the FAD domain of E. coli is rotated 66 degrees with the NADPH domain remaining fixed the two prosthetic groups move into close contact allowing electrons to pass from NADPH to FAD and then to the active site disulfide bond.[1][15] The conserved active site residues in E. coli are -Cys-Ala-Thr-Cys-.[1]
Mammalian
Mammalian TrxRs have a much higher sequence homology with glutathione reductase than E. coli.[1] The active-site Cys residues in the FAD domain and bound NADPH domain are in close proximity removing the necessity for a 66 degree rotation for electron transfer found in E. coli. An additional feature of the mammalian mechanism is the presence of a selenocysteine residue at the C-terminal end of the protein which is required for catalytic activity. The conserved residues in mammalian active site are -Cys-Val-Asn-Val-Gly-Cys-.[1]
Detection methods
Thioredoxin reductase can be quantified by various methods such as the DTNB assay using Ellman's reagent. The disulfide-based TRFS series of fluorescent probes have shown selective detection of TrxR.[16][17][18][19] Mafireyi synthesized the first diselenide probe that was applied in the detection of TrxR.[20][21] Other detection methods include immunological techniques and the selenocystine-thioredoxin reductase assay (SC-TR assay).
Clinical significance
Cancer treatment
Since the activity of this enzyme is essential for cell growth and survival, it is a good target for anti-tumor therapy. Furthermore, the enzyme is upregulated in several types of cancer, including
Cardiomyopathy
Dilated cardiomyopathy (
Antibiotic
There has recently been some research to show that low molecular weight thioredoxin reductase could be a target for novel antibiotics (such as auranofin or Ebselen.[25]) This is especially true for Mycobacterium Haemophilum, and could be used for antibiotic resistant bacteria.[26]
References
- ^ PMID 10657232.
- PMID 9218434.
- PMID 23675692.
- ISSN 0970-4140.
- ^ PMID 12379950.
- ^ PMID 20494123.
- PMID 19691428.
- PMID 17115886.
- PMID 9108027.
- ^ PMID 15485910.
- ^ S2CID 26055087.
- ^ PMID 11481439.
- PMID 10801974.
- PMID 11495589.
- PMID 9235991.
- PMID 31227705.
- PMID 27709154.
- S2CID 225082279.
- PMID 26725656.
- S2CID 229142596.
- ISSN 2211-7156.
- PMID 16934670.
- PMID 11307155.
- PMID 21247928.
- PMID 30642940.
- PMID 25831516.
External links
- Thioredoxin+Reductase+(NADPH) at the U.S. National Library of Medicine Medical Subject Headings (MeSH)