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 has 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. Following purification, AtGSTZ1-1 was assayed for a range of activities and compared with other purified recombinant plant GSTs from the phi, tau, and theta classes. AtGSTZ1-1 differed from the other GSTs in showing no glutathione conjugating activity toward xenobiotics and no glutathione peroxidase activity toward organic hydroperoxides. Uniquely among the plant GSTs, AtGSTZ1-1 showed activity as a maleylacetone isomerase (MAI). This glutathione-dependent reaction is analogous to the cis-trans isomerization of maleylacetoacetate to fumarylacetoacetate, which occurs in the course of tyrosine catabolism to acetoacetate and fumarate. Thus, rather than functioning as a conventional GST, AtGSTZ1-1 appears to be involved in tyrosine degradation. In addition to the MAI activity, the AtGSTZ1-1 also catalyzed the glutathione-dependent dehalogenation of dichloroacetic acid to glyoxylic acid. This latter activity was used to demonstrate the presence of functional AtGSTZ1-1 inplanta.
Dixon
D P
DP
Department of Biological Sciences, University of Durham, United Kingdom.
Cole
D J
DJ
Edwards
R
R
D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins; D001483:Base Sequence; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics; D017343:Genes, Plant; D005982:Glutathione Transferase / Q000235:genetics* / Q000378:metabolism*; D006713:Homogentisic Acid / Q000378:metabolism; D008969:Molecular Sequence Data; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism*; D019745:cis-trans-Isomerases / Q000378:metabolism
D029681:Arabidopsis Proteins; D014443:Tyrosine; C428046:GSTZ1 protein, Arabidopsis; D005982:Glutathione Transferase; D019745:cis-trans-Isomerases; C023933:maleylacetone isomerase; D006713:Homogentisic Acid