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THIOREDOXIN A ACTIVE SITE MUTANTS FORM MIXED DISULFIDE DIMERS THAT RESEMBLE ENZYME-SUBSTRATE REACTION INTERMEDIATE
Structural highlights
FunctionTHIO_BACSU Participates in various redox reactions through the reversible oxidation of its active center dithiol to a disulfide and catalyzes dithiol-disulfide exchange reactions. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThioredoxin functions in nearly all organisms as the major thiol-disulfide oxidoreductase within the cytosol. Its prime purpose is to maintain cysteine-containing proteins in the reduced state by converting intramolecular disulfide bonds into dithiols in a disulfide exchange reaction. Thioredoxin has been reported to contribute to a wide variety of physiological functions by interacting with specific sets of substrates in different cell types. To investigate the function of the essential thioredoxin A (TrxA) in the low-GC Gram-positive bacterium Bacillus subtilis, we purified wild-type TrxA and three mutant TrxA proteins that lack either one or both of the two cysteine residues in the CxxC active site. The pure proteins were used for substrate-binding studies known as "mixed disulfide fishing" in which covalent disulfide-bonded reaction intermediates can be visualized. An unprecedented finding is that both active-site cysteine residues can form mixed disulfides with substrate proteins when the other active-site cysteine is absent, but only the N-terminal active-site cysteine forms stable interactions. A second novelty is that both single-cysteine mutant TrxA proteins form stable homodimers due to thiol oxidation of the remaining active-site cysteine residue. To investigate whether these dimers resemble mixed enzyme-substrate disulfides, the structure of the most abundant dimer, C32S, was characterized by X-ray crystallography. This yielded a high-resolution (1.5A) X-ray crystallographic structure of a thioredoxin homodimer from a low-GC Gram-positive bacterium. The C32S TrxA dimer can be regarded as a mixed disulfide reaction intermediate of thioredoxin, which reveals the diversity of thioredoxin/substrate-binding modes. Thioredoxin A active-site mutants form mixed disulfide dimers that resemble enzyme-substrate reaction intermediates.,Kouwen TR, Andrell J, Schrijver R, Dubois JY, Maher MJ, Iwata S, Carpenter EP, van Dijl JM J Mol Biol. 2008 Jun 6;379(3):520-34. Epub 2008 Apr 10. PMID:18455736[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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