On the interaction between [Ru(NH3)6]3 + and the G-quadruplex forming thrombin binding aptamer sequence

• Strong interaction between 2 [Ru(NH3)6]3 + and one thrombin binding aptamer (TBA).
• It was evidenced independently by circular dichroism and electrochemistry.
• The interaction differs from the conventional electrostatic charge compensation.
• It takes place both in solution and when TBA is immobilised at gold surfaces.
• The finding is significant for metal-DNA studies and in the field of aptasensors.

The interaction between the thrombin binding aptamer (TBA), a G-quadruplex forming DNA sequence, and the electroactive hexaammineruthenium(III) cation has been studied by electrochemical methods and circular dichroism spectroscopy. When TBA is immobilised on a gold surface in a typical aptasensor configuration, the [Ru(NH3)6]3 + cation can be bound to the electrode surface through its interaction with the TBA sequence. This interaction is strong enough to enable the ruthenium complex to remain at the surface when the electrode is immersed in an electrolyte free of [Ru(NH3)6]3 +, meaning that the complex does not diffuse back into the solution. A stoichiometry of 2 [Ru(NH3)6]3 + per TBA strand has been determined, indicating that the interaction differs from the conventional, non-specific electrostatic charge compensation, for which a 5 to 1 ratio would be expected between the triply charged cation and the 15 bases sequence. It is shown that this interaction takes place not only at the surface, but also when both TBA and hexaammineruthenium(III) are dissolved in solution. Under such conditions, a similar stoichiometry of 2 [Ru(NH3)6]3 + per TBA strand has been evidenced by two independent methods, namely circular dichroism spectroscopy and differential pulse voltammetry.

Hexaammineruthenium can be tightly bound to the thrombin binding aptamer, an anti-parallel G-quadruplex forming DNA sequence. A 2:1 stoichiometry is found, markedly different from the 5:1 ratio expected on the basis of a simple electrostatic charge compensation.Figure optionsDownload as PowerPoint slide