Dpto. Química Física, Bioquímica y Química Inorgánica, Universidad de Almería, Carretera Sacramento s/n, Almería 04120, Spain
Abstract:
The binding of glutathione (GSH) to the tyrosine 7 to phenylalanine mutant of Schistosoma japonicum glutathione S-transferase (SjGST-Y7F) has been studied by isothermal titration calorimetry (ITC). At pH 6.5 and 25 °C this mutant shows a higher affinity for glutathione than wild type enzyme despite an almost complete loss of activity in the presence of 1-chloro-2,4-dinitrobenzene (CDNB) as second substrate. The enthalpy change upon binding of GSH is more negative for the mutant than for the wild type GST (SjGST). Changes in accessible solvent areas (ASA) have been calculated based on enthalpy and heat capacity changes. ASA values indicated the burial of apolar surfaces of protein and ligand upon binding. A more negative ΔCp value has been obtained for the mutant enzyme, suggesting a more hydrophobic interaction, as may be expected from the change of a tyrosine residue to phenylalanine.