The contribution of the C-terminal sequence to the catalytic activity of GST2, a human alpha-class glutathione transferase.

A plasmid vector was constructed that encodes the expression in Escherichia coli of a truncated form of GST2, a human Alpha-class glutathione transferase. The truncated enzyme, GST2del210, has 12 residues deleted from the C-terminus and has the last two residues of the new C-terminal mutated from aspartic acid and glutamic acid to histidine and glycine respectively. GST2del210 has substantially diminished specific activity with either 1-chloro-2,4-dinitrobenzene or cumene hydroperoxide as substrate. The affinity of the truncated enzyme for a GSH-agarose matrix was also diminished, but sufficient interaction remained to enable affinity purification. Inhibition of GST2del210 by bromosulphophthalein was not altered. In contrast, this truncated form was not inhibited by S-pentylglutathione, a competitive inhibitor of the wild-type GST2 isoenzyme. The results show that the C-terminal segment of the Alpha-class glutathione transferases may form a component of the hydrophobic substrate-binding site. In contrast, this region appears not to be directly involved in GSH binding and is not absolutely essential for catalytic activity.