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HUMAN THIOREDOXIN DOUBLE MUTANT WITH CYS 32 REPLACED BY SER AND CYS 35 REPLACED BY SER
Structural highlights
FunctionTHIO_HUMAN Participates in various redox reactions through the reversible oxidation of its active center dithiol to a disulfide and catalyzes dithiol-disulfide exchange reactions. Plays a role in the reversible S-nitrosylation of cysteine residues in target proteins, and thereby contributes to the response to intracellular nitric oxide. Nitrosylates the active site Cys of CASP3 in response to nitric oxide (NO), and thereby inhibits caspase-3 activity. Induces the FOS/JUN AP-1 DNA-binding activity in ionizing radiation (IR) cells through its oxidation/reduction status and stimulates AP-1 transcriptional activity.[1] [2] [3] [4] [5] ADF augments the expression of the interleukin-2 receptor TAC (IL2R/P55).[6] [7] [8] [9] [10] 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 PubMedBACKGROUND: Human thioredoxin reduces the disulfide bonds of numerous proteins in vitro, and can activate transcription factors such as NFkB in vivo. Thioredoxin can also act as a growth factor, and is overexpressed and secreted in certain tumor cells. RESULTS: Crystal structures were determined for reduced and oxidized wild type human thioredoxin (at 1.7 and 2.1 A nominal resolution, respectively), and for reduced mutant proteins Cys73-->Ser and Cys32-->Ser/Cys35-->Ser (at 1.65 and 1.8 A, respectively). Surprisingly, thioredoxin is dimeric in all four structures; the dimer is linked through a disulfide bond between Cys73 of each monomer, except in Cys73-->Ser where a hydrogen bond occurs. The thioredoxin active site is blocked by dimer formation. Conformational changes in the active site and dimer interface accompany oxidation of the active-site cysteines, Cys32 and Cys35. CONCLUSIONS: It has been suggested that a reduced pKa in the first cysteine (Cys32 in human thioredoxin) of the active-site sequence is important for modulation of the redox potential in thioredoxin. A hydrogen bond between the sulfhydryls of Cys32 and Cys35 may reduce the pKa of Cys32 and this pKa depression probably results in increased nucleophilicity of the Cys32 thiolate group. This nucleophilicity, in tum, is thought to be necessary for the role of thioredoxin in disulfide-bond reduction. The physiological role, if any, of thioredoxin dimer formation remains unknown. It is possible that dimerization may provide a mechanism for regulation of the protein, or a means of sensing oxidative stress. Crystal structures of reduced, oxidized, and mutated human thioredoxins: evidence for a regulatory homodimer.,Weichsel A, Gasdaska JR, Powis G, Montfort WR Structure. 1996 Jun 15;4(6):735-51. PMID:8805557[11] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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