The structure of a zeta class glutathione S-transferase from Arabidopsis thaliana: Characterisation of a GST with novel active-site architecture and a putative role in tyrosine catabolism

The cis-trans isomerisation of maleylacetoacetate to fumarylacetoacetate is the penultimate step in the tyrosine/phenylalanine catabolic pathway and h as recently been shown to be catalysed by glutathione S-transferase enzymes belonging to the zeta class. Given this primary metabolic role it is unsur prising that zeta class glutathione S-transferases are well conserved over a considerable period of evolution, being found in vertebrates, plants, ins ects and fungi. The structure of this glutathione S-transferase, cloned fro m Arabidopsis thaliana, has been solved by single isomorphous replacement w ith anomalous scattering and refined to a final crystallographic R-factor o f 19.6% using data from 25.0 Angstrom to 1.65 Angstrom. The zeta class enzy me adopts the canonical glutathione S-transferase fold and forms a homodime r with each subunit consisting of 221 residues. In agreement with structure s of glutathione S-transferases from the theta and ph classes, a serine res idue (Ser17) is present in the active site, at a position that would allow it to stabilise the thiolate anion of glutathione. Site-directed mutagenesi s of this residue confirms its importance in catalysis. In addition, the ro le of a highly conserved cysteine residue (Cys19) present in the active sit e of the zeta class glutathione S-transferase enzymes is discussed. (C) 200 1 Academic Press.