Exploring the molecular mechanism of hA1-1 glutathione S-transferase, focusing on the role of the characteristic C-terminal helix.

The molecular mechanism of hAl-1 glutathione S-transferase (GST) has been probed using fluorescence and NMR spectroscopy, kinetic analysis and X-ray crystallography. The results show that the mechanism of hAl-1 GST involves hydrophobic substrate activation, and the efficiency of this process is a crucial factor in hydrophobic substrate specificity. Hydrophobic substrate activation can only occur when the glutathione peptidyl moiety has bound, inducing a conformational change in the protein. The main region of the protein that is involved in this conformational change is the characteristic C-terminal helix of hAl-1 GST and the integrity of this region has been shown to be essential for hydrophobic substrate activation. It is thought that the C-terminal helix correctly orientates the hydrophobic substrate in the active site allowing activation to occur. The deletion of the C-terminal helix alters the substrate specificity of the enzyme, with the truncated enzyme having a high activity towards ethacrynic acid, normally a pi-class GST substrate. Thus the characteristic C-terminal helix of alpha class GSTs is a major determinant in substrate specificity, in particular determining the characteristic substrate specificity of hAl-1 GST.