Thermodynamics and structure of a DNA tetraplex: A spectroscopic and calorimetric study of the tetramolecular complexes of d(TG3T) and d(TG3T2G3T)

Renzhe Jim, Barbara L. Gaffney, Chuan Wang, Roger A. Jones, Kenneth J. Breslauer

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Abstract

We report a combined thermodynamic and structural characterization of a DNA tetraplex. Using spectroscopic and calorimetric techniques, we demonstrate that d(TG3T) and d(TG3T2G3T), in the presence of K+, form stable tetramolecular complexes. From differential scanning calorimetry measurements, we obtain the following thermodynamic profiles for formation of each tetraplex at 25°C: ΔG° = -6.9 kcal/mol of tetraplex (or -2.3 kcal/mol of tetrad; 1 cal = 4.184 J), ΔH° = -62.6 kcal/mol of tetraplex (or -20.9 kcal/mol of tetrad), and ΔS° = -186.9 cal·K-1·mol-1 of tetraplex (or -62.3 cal·K-1·mol-1 of tetrad) for the d(TG3T) tetraplex; and ΔG° = -20.2 kcal/mol of tetraplex (or -3.4 kcal/mol of tetrad), ΔH° = -123.2 kcal/mol of tetraplex (or -20.5 kcal/mol of tetrad), and ΔS° = -346.0 cal·K-1·mol-1 of tetraplex (or -57.7 cal·K-1-mol-1 of tetrad) for the d(TG3T2G3T) tetraplex. These data demonstrate that at 25°C a G-tetrad can exhibit considerable stability, comparable to or even exceeding that of most Watson-Crick nearest-neighbor interactions, with this stability resulting from a very favorable enthalpy of formation. Temperature-dependent CD measurements reveal that the melting temperatures of both tetraplexes exhibit unusually low salt dependences. This unexpected behavior may reflect a diminished charge density due to bound K+ ions. For each complex, the Na+ and K+ forms exhibit drastically different isothermal and temperature-dependent CD profiles, with the K+ forms of each tetraplex melting more sharply and at a higher temperature than the Na+ forms. Using one- and two-dimensional NMR techniques, we show that the strands in the tetramolecular complex of d(TG3T),K+ are all parallel and that the guanine glycosidic conformations are all anti.

Original languageEnglish (US)
Pages (from-to)8832-8836
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume89
Issue number18
StatePublished - 1992

All Science Journal Classification (ASJC) codes

  • General

Keywords

  • CD
  • Differential scanning calorimetry
  • Energetics
  • G-tetrads
  • NMR

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