Monitoring the Temperature Unfolding of G-Quadruplexes by UV and Circular Dichroism Spectroscopies and Calorimetry Techniques
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DNA oligonucleotides containing guanine repeat sequences can adopt G-quadruplex (GQ) structures in the presence of specific metal ions. We report on how to use a combination of spectroscopic and calorimetric techniques to determine the spectral characteristics and thermodynamic parameters for the temperature-unfolding of GQs. Specifically, we investigated the unfolding of d(G2 T2 G2 TGTG2 T2 G2 ), G2 , and d(G3 T2 G3 TGTG3 T2 G3 ), G3 by a combination of UV and circular dichroism (CD) spectroscopies, and differential scanning calorimetry (DSC).
Analysis of the UV and CD spectra of these GQs at low (100% helix) and high (100% random coil) temperatures yielded the optimal wavelengths to determine the melting curves. In addition, the CD spectra yielded the particular conformation(s) that each GQ adopted at low temperature. DSC curves yielded complete thermodynamic profiles for the unfolding of each GQ. We use these profiles to determine the thermodynamic contributions for the formation of a G-quartet stack.
