Gene structure, expression and chromosomal localization of murine Theta class glutathione transferase mGSTT1-1

We have isolated and characterized a cDNA and partial gene encoding a murin e subfamily 1 Theta class glutathione transferase (GST), The cDNA derived f rom mouse GSTT1 has an open reading frame of 720 bp encoding a peptide of 2 40 amino acids with a calculated molecular mass of 27356 Da. The encoded pr otein shares only 51%, deduced amino acid sequence identity with mouse GSTT 2, but greater than 80%, deduced amino acid sequence identity with rat GSTT 1 and human GSTT1. Mouse GSTT1-1 was expressed in Escherichia coli as an N- terminal 6 x histidine-tagged protein and purified using immobilized-metal affinity chromatography on nickel-agarose. The yield of the purified recomb inant protein from E. coli cultures was approx. 14 mg/l. Recombinant mouse GSTTI-1 was catalytically active towards 1,2-epoxy-3-(p-nitrophenoxy)propan e. 4-nitro-benzyl chloride and dichloromethane, Low activity towards 1-mena phthyl sulphate and 1-chloro-2,4-dinitrobenzene was detected, whereas mouse GSTT1-1 was inactive towards ethacrynic acid. Recombinant mouse GSTT1-1 ex hibited glutathione peroxidase activity towards cumene hydroperoxide and t- butyl hydroperoxide, but was inactive towards a range of secondary lipid-pe roxidation products, such as the trans-alk-2-enals and trans,trans-alka-2,4 -dienals. Mouse GSTT1 mRNA is most abundant in mouse liver and kidney, with some expression in intestinal mucosa, Mouse GSTT1 mRNA is induced in liver by phenobarbital, but not by butylated hydroxyanisole, beta-napthoflavone or isosafrole, The structure of mouse GSTT1 is conserved with that of the s ubfamily 2 Theta class GST genes mouse GSTT2 and rat GSTT2, comprising five exons interrupted by four introns, The mouse GSTT1 gene was found, by in s itu hybridization, to be clustered with mouse GSTT2 on chromosome 10 at ban ds B5-C1. This region is syntenic with the location of the human Theta clas s GSTs clustered on chromosome 22q11.2. Similarity searches of a mouse-expr essed sequence tag database suggest that there may be two additional member s of the Theta class that share 70% and 88% protein sequence identity with mouse GSTT1, but less than 55% sequence identity with mouse GSTT2.