Thiol-specific antioxidant (TSA) from yeast contains cysteine residues at amino acid positions 47 and 170 but is not associated with obvious redox cofactors. These two cysteines are highly conserved in a family of proteins that exhibit sequence identity of 23-98% with TSA. The roles of Cys-47 and Cys-170 in yeast TSA were investigated by replacing them individually with serine and expressing the mutant TSA proteins (RC47S and RC170S, respectively), as well as wild-type TSA (RWT), in Escherichia coli. Wild-type TSA purified from yeast (YWT) and RWT were both shown to exist predominantly as dimers, whereas RC47S and RC170S existed mainly as monomers under a denaturing condition. This observation suggests that the dimerization of YWT and RWT requires disulfide linkage of Cys-47 and Cys-170. The presence of the Cys-47-Cys-170 linkage in YWT was directly shown by isolation of dimeric tryptic peptides, one monomer of which contained Cys-47 and the other contained Cys-170. A small percentage of YWT, RWT, RC47S, and RC170S molecules formed dimers linked by Cys-47-Cys-47 or Cys-170-Cys-170 disulfide bonds. The antioxidant activity of the various TSA proteins was evaluated from their ability to protect glutamine synthetase against the dithiothreitol/Fe3+/O2 oxidation system. YWT, RWT, and RC170S were equally protective, whereas RC47S was completely ineffective. Thus, Cys-47, but not Cys-170, constitutes the site of oxidation by putative substrate.
|Evidence ID||Analyze ID||Interactor||Interactor Systematic Name||Interactor||Interactor Systematic Name||Type||Assay||Annotation||Action||Modification||Phenotype||Source||Reference||Note|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Gene Ontology Term||Gene Ontology Term ID||Qualifier||Aspect||Method||Evidence||Source||Assigned On||Reference||Annotation Extension|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Phenotype||Experiment Type||Experiment Type Category||Mutant Information||Strain Background||Chemical||Details||Reference|
|Evidence ID||Analyze ID||Regulator||Regulator Systematic Name||Target||Target Systematic Name||Experiment||Conditions||Strain||Source||Reference|