Characterisation of a zeta class glutathione transferase from Arabidopsis thaliana with a putative role in tyrosine catabolism

A glutathione transferase (GST) similar to zeta GSTs in animals and fungi h as been cloned from Arabidopsis thaliana using RT-PCR. The Arabidopsis zeta GST (AtGSTZ1) was expressed in Escherichia coli as his-tagged polypeptides , which associated together to form the 50-kDa AtGSTZ1-1 homodimer. Followi ng purification, AtGSTZ1-1 was assayed for a range of activities and compar ed with other purified recombinant plant GSTs from the phi, tau, and theta classes. AtGSTZ1-1 differed from the other GSTs in showing no glutathione c onjugating activity toward xenobiotics and no glutathione peroxidase activi ty toward organic hydroperoxides. Uniquely among the plant GSTs, AtGSTZ1-1 showed activity as a maleylacetone isomerase (MAI). This glutathione-depend ent reaction is analogous to the cis-trans isomerization of maleylacetoacet ate to fumarylacetoacetate, which occurs in the course of tyrosine cataboli sm to acetoacetate and fumarate. Thus, rather than functioning as a convent ional GST, AtGSTZ1-1 appears to be involved in tyrosine degradation. In add ition to the MAI activity, the AtGSTZ1-1 also catalyzed the glutathione-dep endent dehalogenation of dichloroacetic acid to glyoxylic acid. This latter activity was used to demonstrate the presence of functional AtGSTZ1-1 in p lanta. (C) 2000 Academic Press.