The impact of water molecules on binding affinity of the anti-diabetic thiazolidinediones for catalase: Kinetic and mechanistic approaches.

Water molecules play a vital role in efficient drug binding to its target. Thiazolidinediones (TZDs), a class of anti-diabetic drugs, are widely used for treatment of type 2 diabetes mellitus. In the present study, the possible contribution of water molecules to the binding of TZDs to catalase, a potential target in the liver, was investigated by different experimental and theoretical methods. These studies indicated that TZDs could significantly improve the catalase catalytic function with a significant contribution from water molecules. As a probe for the differential number of released water molecules during the catalase transition from E to E* states, the activity of TZDs-catalase complexes was demonstrated to be mainly dependent on water activity. However, free catalase decomposed the substrate more independently. In addition, the spectrofluorimetry studies showed that the binding of TZDs to catalase needed the release of water molecules from the enzyme's binding pocket. The thermodynamic studies indicated that the binding enthalpy and entropy of TZDs for catalase were decreased with lower water activity. The favorable process contributes to release of water molecules from the binding pocket through the formation of hydrophobic interactions between catalase and TZDs in an enthalpic manner. Molecular docking simulations confirmed that the depletion of water molecules from the binding cavity is essential for effective interactions between TZDs and catalase.