Crystal structure of herbicide-detoxifying maize glutathione S-transferase-I in complex with lactoylglutathione: Evidence for an induced-fit mechanism

Glutathione S-transferases (GSTs) -I and -III are involved in herbicide metabolism in maize and have been intensively studied. Starting with plant tissue from Zen mays var. mutin recombinant GST-I was prepared by heterologous expression in Escherichia coli. The enzyme was crystallized in the presence of lactoylglutathione, a ligand formerly never observed in a GST structure and known as an intermediate of the pharmacologically relevant glyoxalase system. The crystal structure of GST-I has been determined at 2.5 Angstrom resolution and exhibits the GSP-typical dimer of two identical subunits, each consisting of 214, residues. Compared with other plant GSTs the three-dimensional structure of GST-I primarily shows structural differences in the hydrophobic substrate binding site, the linker segment and the C-terminal region. Furthermore, a comparison of the ligand-bound GST-I structure with the apo structure of GST-III indicates the movement of a ten-residue loop upon binding of the ligand to the active site. This is the first structure-based evidence for an induced Lit mechanism of glutathione S-transferases, which has previousely been postulated for class pi enzymes. Together with GST-III, GST-I may explain herbicide resistance and selectivity in maize as well as in other agronomic relevant crops. (C) 1997 Academic Press Limited.