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thioredoxin pathway

General Background The thiol redox system of Escherichia coli consists of the thioredoxin pathway (shown here) and the glutathione/glutaredoxin pathway (see : GLUT-REDOX-PWY). Electrons from NADPH flow through these pathways via gradients in redox potentials. Thioredoxin and glutaredoxin reduce disulfide bonds by a thiol-disulfide exchange mechanism involving two active site cysteine residues in the motif CXXC (where X is any amino acid) that form either a disulfide or a dithiol. In addition to the importance of thiol redox potential , other important factors in the thiol redox system are cellular location and the overall redox state of the cell. Both the thioredoxin and glutathione pathways appear to operate in parallel. Genetic studies in E. coli have shown the two pathways to be functionally redundant during aerobic growth, although inactivation of both pathways results in unviability. Reviewed in . The thioredoxin pathway is involved in reducing important cytoplasmic enzymes such as the essential ribonucleotide reductase, as well as 3'-phosphoadenosine-5'-phosphosulfate reductase and methionine sulfoxide reductases A and B. E. coli thioredoxin also binds to bacteriophage T7 DNA polymerase and serves as its processivity factor for polymerization during phage growth ( and in ). In addition, many other proteins that may interact with thioredoxin have been identified . Thioredoxin is also involved in a pathway for the trans-membrane transfer of reducing potential from the cytoplasm to the periplasm to reduce the protein disulfide isomerase DbsC . After acting as a reductant, disulfide-containing oxidized thioredoxin is reduced back to a dithiol by thioredoxin reductase, an FAD-containing, NADPH-dependent enzyme. Reviewed in . The thiol redox system is present in taxonomic groups from archaea to man. However, despite structural and mechanistic similariteis between prokaryotic and eukaryotic thiol redox systems, their overall cellular functions differ (reviewed in and ). About This Pathway In this pathway diagram, clicking on the protein class named "a reduced thioredoxin" will display a page showing two instances of this class named reduced thioredoxin 2 and thioredoxin 1. As shown in the gene-reaction schematic on this page, these proteins are the products of genes trxC and trxA, respectively. Clicking on either of the instance names (or on their gene or protein symbols in the gene-reaction schematic) will display a page showing some structural and functional properties of the respective protein. Again in the pathway diagram, clicking on the protein class named "an oxidized thioredoxin" will display a page showing two instances of this class named oxidized thioredoxin and oxidized thioredoxin 2. Note that in the gene-reaction schematic shown on this page the reduced thioredoxins are considered to be the direct gene products and their oxidized forms are shown separately as modified forms of the gene products. In E. coli TrxA is a more well studied thiol-disulfide oxidoreductase than TrxC (Trx2). TrxC was identified later as a novel thioredoxin that forms a subfamily of the TrxA protein family. The gene encoding TrxC is under control of the transcriptional regulator OxyR which responds to oxidative stress, although the biological role of TrxC remains to be fully elucidated .

from BIOCYC source record: ECO_THIOREDOX-PWY
Type: pathway
Taxonomic scope
:
organism-specific biosystem
Organism
:
Escherichia coli
BSID:
83

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