Influence of K+ Ions on Thermodynamic Stability of DNA G-Quadruplex

It is supposed that presence of monovalent cations is necessary for in vitro formation of G-quadruplex, and the most effective cation is K. We demonstrated that 15-mer sequences like GGG(TGGG)3 (abbreviated name G3T) are capable to form stable quadruplexes even in double-distilled water with heat transition parameters: H = 2.15 kcal/mol, T m = 34.0° C andTm = 34.5° C. In the range of K ion concentrations from 12 μM to 3 mM inclusive, an intensive increase in quadruplex melting temperature Tm, moderate decrease in melting width Tm and intensive increase in melting enthalpy H to 6.6 kcal/mol are observed. On the basis of CD melting curves we have calculated H; dependence curve H = f(Tm) was built; and heat capacity increment Cm = (1.56 ± 0.17) kcal/ K.mol was calculated. The extremely high value of heat capacity increment is in a good agreement with theoretical suggestions, according to which DNA G-quadruplexes are highly flexible. © 2017 Bull. Georg. Natl. Acad. Sci.