Calorimetric investigation on the interaction of proflavine with human telomeric G-quadruplex DNA

• Energetics of the interaction of proflavine with G-quadruplex DNA is presented.
• The binding was exothermic and driven by negative enthalpy and positive entropy.
• The binding was characterized by enthalpy–entropy compensation.
• DSC studies revealed that proflavine stabilized the quadruplex significantly.

The interaction of an acridine dye, proflavine, with human telomeric G-quadruplex DNA was characterized by isothermal titration calorimetry and differential scanning calorimetry. The equilibrium constant of binding was deduced to be (1.36 ± 0.09) · 106 M−1 at T = 298.15 K. The binding reaction was driven by both negative enthalpy and positive entropy contributions. The equilibrium constant decreased and the reaction became increasingly enthalpy driven with rise in temperature. However, the standard molar Gibbs energy change exhibited only marginal alterations suggesting the occurrence of enthalpy–entropy compensation. Negative heat capacity values were also obtained from the temperature dependence of enthalpy change. Parsing of the standard molar Gibbs energy using the salt dependent calorimetric data revealed that the binding was dominated by non-polyelectrolytic forces which remained virtually unaltered with changing salt concentration. Proflavine binding also significantly enhanced the thermal stability of G-quadruplex DNA against thermal unfolding.