Identification of mixed di-cation forms of G-quadruplex in solution.

Abstract

Multinuclear NMR study has demonstrated that G-quadruplex adopted by d(G3T4G4) exhibits two cation binding sites between three of its G-quartets. Titration of tighter binding K+ ions into the solution of d(G3T4G4)2 folded in the presence of 15NH4+ ions uncovered a mixed mono-K+-mono-15NH4+ form that represents intermediate in the conversion of di-15NH4+ into di-K+ form. Analogously, 15NH4+ ions were found to replace Na+ ions inside d(G3T4G4)2 quadruplex. The preference of 15NH4+ over Na+ ions for the two binding sites is considerably smaller than the preference of K+ over 15NH4+ ions. The two cation binding sites within the G-quadruplex core differ to such a degree that 15NH4+ ions bound to the site, which is closer to the edge-type loop, are always replaced first during titration by K+ ions. The second binding site is not taken up by K+ ion until K+ ion already resides at the first binding site. Quantitative analysis of concentrations of the three di-cation forms, which are in slow exchange on the NMR time scale, at 12 K+ ion concentrations afforded equilibrium binding constants. K+ ion binding to sites U and L within d(G3T4G4)2 is more favorable with respect to 15NH4+ ions by Gibbs free energies of approximately -24 and -18 kJ mol(-1) which includes differences in cation dehydration energies, respectively.

• Authors: Primoz Sket, Martin Crnugelj, Janez Plavec
• Journal: Nucleic acids research (Nucleic Acids Res) Vol. 33 Issue 11 Pg. 3691-7 ( 2005) ISSN: 1362-4962 [Electronic] England
• PMID: 15985684 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Cations
• Oligonucleotides
• Quaternary Ammonium Compounds
• d(G3T4G4)2
• Guanine
• DNA
• Potassium

Topics

• Binding Sites
• Cations (chemistry)
• DNA (chemistry)
• G-Quadruplexes
• Guanine (chemistry)
• Nuclear Magnetic Resonance, Biomolecular
• Oligonucleotides (chemistry)
• Potassium (chemistry)
• Quaternary Ammonium Compounds (chemistry)