Measuring Excess Heat Capacities of Deoxyribonucleic Acid (DNA) Folding at the Single-Molecule Level

Measurements of the thermodynamic properties of biomolecular folding (Delta G degrees, Delta H degrees, Delta S degrees, etc.) provide a wealth of information on the folding process and have long played a central role in biophysical investigation. In particular, the excess heat capacity of folding (Delta C-P) is crucial, as typically measured in bulk ensemble studies by differential scanning calorimetry (DSC) and isothermal titration calorimetry (ITC). Here, we report the first measurements of Delta C-P at the single-molecule level using the single-molecule fluorescence resonance energy transfer (smFRET) as well as the very first measurements of the heat capacity change associated with achieving the transition state (Delta C-P(double dagger)) for nucleic acid folding. The deoxyribonucleic acid (DNA) hairpin used in these studies exhibits an excess heat capacity for hybridization (Delta C-P = -340 +/- 60 J/mol/K per base pair) consistent with the range of literature expectations (Delta C-P = -100 to -420 J/mol/K per base pair). Furthermore, the measured activation heat capacities (Delta C-P(double dagger)) for such hairpin unfolding are consistent with a folding transition state containing few fully formed base pairs, in agreement with prevailing models of DNA hybridization.

Automated summary

The study measured the heat capacity changes in DNA folding at the single-molecule level and the transition state, finding that the results were consistent with previous literature expectations.