A non-active site residue, cysteine 69, of glutathione S-transferase ADGSTD3-3 has a role in stability and catalytic function

The Cys69 residue of an Anopheles dirus glutathione S-transferase isoform (adGSTD3-3), was characterized to elucidate its contribution in both catalysis and structural support. Nine mutants were generated at this position by replacing the residue with polar, non-polar and charged residues. The polar residues changed the Vm of the enzymes. With non-polar residues, the enzymes were unable to fold and were expressed in the insoluble inclusion form. With charged residues, the soluble enzyme yields were only 3% of the wild type protein. Molecular dynamics simulation also was performed to understand the changes in the enzyme structure. These findings are additional evidence of the importance of structural residues that affect the enzymatic properties such as Vm, Km and enzyme specificity.