Binding of the anticancer alkaloid sanguinarine with tRNAphe: spectroscopic and calorimetric studies

Abstract

The interaction of the natural plant alkaloid and anticancer agent sanguinarine with tRNAphe has been investigated by spectroscopic and calorimetric techniques. Sanguinarine iminium binds to tRNAphe cooperatively; alkanolamine does not bind but in presence of large tRNAphe concentration, a conversion from alkanolamine to iminium occurs resulting in concomitant binding of the latter. The binding affinity of the iminium to tRNAphe obtained from isothermal titration calorimetry was of the order of 105 M−1, which is close to that evaluated from spectroscopy. The binding was driven largely by negative enthalpy and a smaller but favourable positive entropy change. The binding was dependent on the [Na+] concentration, but had a larger non-electrostatic contribution to the Gibbs energy. A small heat capacity value and the enthalpy–entropy compensation in the energetics of the interaction characterized the binding of the iminium form to tRNAphe. This study confirms that the tRNAphe binding moiety is the iminium form of sanguinarine.