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Molecules 2018, 23(7), 1806; https://doi.org/10.3390/molecules23071806

Linking Temperature, Cation Concentration and Water Activity for the B to Z Conformational Transition in DNA

1
Estee Lauder Companies, Inc., Melville, NY 11747, USA
2
Department of Chemistry and Biochemistry, Texas Woman’s University, Denton, TX 76204, USA
*
Author to whom correspondence should be addressed.
Received: 18 June 2018 / Revised: 18 July 2018 / Accepted: 19 July 2018 / Published: 21 July 2018
(This article belongs to the Collection New Frontiers in Nucleic Acid Chemistry)
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Abstract

High concentrations of Na+ or [Co(NH3)6]3+ can induce the B to Z conformational transition in alternating (dC-dG) oligo and polynucleotides. The use of short DNA oligomers (dC-dG)4 and (dm5C-dG)4 as models can allow a thermodynamic characterization of the transition. Both form right handed double helical structures (B-DNA) in standard phosphate buffer with 115 mM Na+ at 25 °C. However, at 2.0 M Na+ or 200 μM [Co(NH3)6]3+, (dm5C-dG)4 assumes a left handed double helical structure (Z-DNA) while the unmethylated (dC-dG)4 analogue remains right handed under those conditions. We have previously demonstrated that the enthalpy of the transition at 25 °C for either inducer can be determined using isothermal titration calorimetry (ITC). Here, ITC is used to investigate the linkages between temperature, water activity and DNA conformation. We found that the determined enthalpy for each titration varied linearly with temperature allowing determination of the heat capacity change (ΔCp) between the initial and final states. As expected, the ΔCp values were dependent upon the cation (i.e., Na+ vs. [Co(NH3)6]3+) as well as the sequence of the DNA oligomer (i.e., methylated vs. unmethylated). Osmotic stress experiments were carried out to determine the gain or loss of water by the oligomer induced by the titration. The results are discussed in terms of solvent accessible surface areas, electrostatic interactions and the role of water. View Full-Text
Keywords: B-DNA; Z-DNA; circular dichroism; calorimetry; enthalpy; conformational transitions; heat capacity B-DNA; Z-DNA; circular dichroism; calorimetry; enthalpy; conformational transitions; heat capacity
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Ferreira, J.M.; Sheardy, R.D. Linking Temperature, Cation Concentration and Water Activity for the B to Z Conformational Transition in DNA. Molecules 2018, 23, 1806.

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