Saccharomyces cerevisiae cells have three Omega class glutathione S-transferases acting as 1-Cys thiol transferases
Barreto Parra, Lina Patricia
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The Saccharomyces cerevisiae genome encodes three proteins that Analysis of point mutants derived from wild-type Gto2 indicates display similarities with human GSTOs (Omega class glutathione that, among the three cysteine residues of the molecule, only the S-transferases) hGSTO1-1 and hGSTO2-2. The three yeast pro- residue at position 46 is required for the glutaredoxin activity. teins have been named Gto1, Gto2 and Gto3, and their purified This indicates that the thiol transferase acts through a mono- recombinant forms are active as thiol transferases (glutaredoxins) thiol mechanism. Replacing the active site of the yeast monothiol against HED (β-hydroxyethyl disulphide), as dehydroascorbate glutaredoxin Grx5 with the proposed Gto2 active site containing reductases and as dimethylarsinic acid reductases, while they are Cys46 allows Grx5 to retain some activity against HED. Therefore not active against the standard GST substrate CDNB (1-chloro- the residues adjacent to the respective active cysteine residues in 2,4-dinitrobenzene). Their glutaredoxin activity is also detectable Gto2 and Grx5 are important determinants for the thiol transferase in yeast cell extracts. The enzyme activity characteristics of the activity against small disulphide-containing molecules. Gto proteins contrast with those of another yeast GST, Gtt1. The latter is active against CDNB and also displays glutathione peroxidase activity against organic hydroperoxides such as cumene hydroperoxide, but is not active as a thiol transferase.