Cysteine 10 is critical for the activity of Ochrobactrum anthropi glutathione transferase and its mutation to alanine causes the preferential binding of glutathione to the H-site

The role of the evolutionarily conserved residue Cys10 in Ochrobactrum anthropi glutathione transferase (OaGST) has been examined by replacing it with an alanine. A double mutant C10A/S11A was also prepared. The effect of the replacements on the coniugating and thiotransferase activities, and on the thermal and chemical stability of the enzyme was analyzed. Our data support the view that in OaGST, in contrast with other beta class GSTs that display significant differences in the glutathione-binding site, Cys10 is a key residue for glutathione coniugating activity. Furthermore, analysis of the OaGST-Cys10Ala structure, crystallized in the presence of glutathione, reveals that this mutation causes a switch between the high-affinity G-site and a low-affinity H-site where hydrophobic cosubstrates bind and where we observe the presence of an unexpected glutathione.