Tk. Hitchens et al., Disorder-to-order transition of the active site of human class Pi glutathione transferase, GST P1-1, BIOCHEM, 40(39), 2001, pp. 11660-11669
Glutathione transferases comprise a large family of cellular detoxification
enzymes that function by catalyzing the conjugation of glutathione (GSH) t
o electron-deficient centers on carcinogens and other toxins. NMR methods h
ave been used to characterize the structure and dynamics of a human class p
i enzyme, GST P1-1, in solution. Resonance assignments have been obtained f
or the unliganded enzyme and the GSH and S-hexylglutathione (GS-hexyl) comp
lexes. Differences in chemical shifts between the GSH and GS-hexyl complexe
s suggest more extensive structural differences between these two enzyme-li
gand complexes than detected by previous crystallographic methods. The NMR
studies reported here clearly show that an alpha -helix (alpha2) within the
GSH binding site exists in multiple conformations at physiological tempera
tures in the absence of ligand. A single conformation of alpha2 is induced
by tile presence of either GSH or GS-hexyl or a reduction in temperature to
below 290 K. The large enthalpy of the transition (similar to 150 kJ/mol)
suggests a considerable structural rearrangement of the protein. The Gibbs
free energy for the transition to the unfolded form is on the order of -4 t
o -6 kJ/mol at physiological temperatures (37 degreesC). This order-to-diso
rder transition contributes substantially to the overall thermodynamics of
ligand binding and should be considered in the design of selective inhibito
rs of class pi glutathione transferases.