RESUMO
The Arabidopsis thaliana glutathione S-transferases zeta class (AtGSTZ) is a multi-functional enzyme, which plays important role in cellular metabolism and environmental purification. Error-prone PCR and cycles of DNA shuffling were used to construct a mutagenesis library of AtGSTZ. The screening of the resultant libraries was carried out by a pH indicator dye-based colorimetric assay. Nine mutants which enhanced the dichloroacetic acid dechlorination activity were obtained. Among them, NN23 contained 25 amino acid substitutions with the activity improving 120%, whereas NN20 contained 24 amino acid substitutions with the activity improving 102%. EC1 contained 2 amino acid substitutions with the activity improving 47%. The rest 6 mutants contained one amino acid substitution with their activity increasing from 9% to 60%. The enzymatic characterization showed that all the evolved enzymes increased their catalytic efficiencies towards dichloroacetic acid and binding affinity towards glutathione whereas some of them increased the renaturability. However there is no obvious change in their thermostability. Based on these data, functional residues related to catalysis and refolding of AtGSTZ were discussed.