title: 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.
abstract: The cis-trans isomerisation of maleylacetoacetate to fumarylacetoacetate is the penultimate step in the tyrosine/phenylalanine catabolic pathway and has recently been shown to be catalysed by glutathione S-transferase enzymes belonging to the zeta class. Given this primary metabolic role it is unsurprising that zeta class glutathione S-transferases are well conserved over a considerable period of evolution, being found in vertebrates, plants, insects and fungi. The structure of this glutathione S-transferase, cloned from Arabidopsis thaliana, has been solved by single isomorphous replacement with anomalous scattering and refined to a final crystallographic R-factor of 19.6% using data from 25.0 A to 1.65 A. The zeta class enzyme adopts the canonical glutathione S-transferase fold and forms a homodimer with each subunit consisting of 221 residues. In agreement with structures of glutathione S-transferases from the theta and phi classes, a serine residue (Ser17) is present in the active site, at a position that would allow it to stabilise the thiolate anion of glutathione. Site-directed mutagenesis of this residue confirms its importance in catalysis. In addition, the role of a highly conserved cysteine residue (Cys19) present in the active site of the zeta class glutathione S-transferase enzymes is discussed.
authors.affiliation: Department of Chemistry, University of Glasgow, Glasgow, G12 8QQ, UK.
authors.forename: R
authors.initials: R
authors.lastname: Thom
authors.forename: D P
authors.initials: DP
authors.lastname: Dixon
authors.forename: R
authors.initials: R
authors.lastname: Edwards
authors.forename: D J
authors.initials: DJ
authors.lastname: Cole
authors.forename: A J
authors.initials: AJ
authors.lastname: Lapthorn
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D001665:Binding Sites; D002384:Catalysis; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000378:metabolism; D019281:Dimerization; D005978:Glutathione / Q000378:metabolism; D005982:Glutathione Transferase / Q000737:chemistry* / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed / Q000235:genetics; D009154:Mutation / Q000235:genetics; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D016415:Sequence Alignment; D012694:Serine / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D021122:Protein Subunits; D014443:Tyrosine; D012694:Serine; D005982:Glutathione Transferase; D005978:Glutathione; D003545:Cysteine