Albany 2013: Book of Abstracts
June 11-15 2013
©Adenine Press (2012)
Application of Differential Scanning Calorimetry to Measure the Differential Binding of Ions, Water and Protons in the Unfolding of DNA Molecules
The overall stability of DNA molecules globally depends on base-pair stacking, base pairing, polyelectrolyte effect and hydration contributions. In order to improve our understanding of the role of ions, water and protons in the stability and melting behavior of DNA structures, we report an experimental approach to determine the differential binding of ions (Δnion), water (ΔnW) and protons (ΔnH+) in the helix-coil transition of DNA molecules. A combination of differential scanning calorimetry (DSC) and temperature-dependent UV and CD spectroscopic techniques to investigate the unfolding of a variety of DNA molecules: S.T. DNA, two dodecamers, one undecamer, nine short hairpins as a function of the GC content of their stem, and two triplexes. We determine complete thermodynamic profiles, including all three linking numbers, for the unfolding of each molecule. The CD spectra indicated that all molecules adopted the B-conformation at low temperatures. Thermodynamic profiles obtained from the DSC curves indicate that the favorable folding of each molecule results from the typical compensation of favorable enthalpy and unfavorable entropy contributions, and negligible heat capacity effects. UV and DSC melting curves as a function of salt, osmolyte and proton concentrations yielded releases of ions, water and protons (for the triplex with C+GC base triplets). Therefore, the favorable folding of each DNA molecule results from the formation of base-pair stacks and uptake of water and counterions. The thermodynamic data will be discussed in terms of the effects of DNA length, loop contributions and type of water molecules.
This research is supported by Grant MCB-1122029 from the National Science Foundation.
Chris M. Olson
Department of Pharmaceutical Sciences