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

摘要

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: ΔH~(VH)= 2.15 kcal/mol, T_m = 34.0℃ and T_m = 34.5℃. In the range of K~+ ion concentrations from 12 uM to 3 mM inclusive, an intensive increase in quadruplex melting temperature T , moderate decrease in melting width ΔT_m and intensive increase in melting enthalpy ΔH~(VH) to 6.6 kcal/mol are observed. On the basis of CD melting curves we have calculated ΔH~(VH); dependence curve ΔH~(VH) = f(_m~T) was bui and heat capacity increment ΔC_m = (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.