Thermodynamics and Kinetics of Unfolding of Antiparallel G-Quadruplexes in Anti-Thrombin Aptamers

The process of unfolding of G-quadruplex structure in the RE31 DNA-aptamer and in its complex with thrombin under the action of the fluorescently labeled complementary oligonucleotides of varying length with formation of double-helix structures has been studied. It has been suggested that G-quadruplex unfolding involves formation of an intermediate complex with an oligonucleotide. Thermodynamic parameters and kinetics of unfolding of the free aptamer and its complex with thrombin differ. Extension of the oligonucleotide sequence complementary to G-quadruplex by two nucleotides to cover the so-called "hinge region" had little impact on the conformational transition of G-quadruplex of the free aptamer. However, a pronounced effect has been observed for the aptamer-protein complex. Most likely these differences could be explained by the thrombin-induced conformational transition of the aptamer involving the hinge region.