Heat capacity changes associated with G-quadruplex unfolding.

Area of Science:

• Biochemistry
• Molecular Biology
• Thermodynamics

Background:

• G-quadruplexes are four-stranded DNA structures involved in genomic regulation.
• Thermodynamic stability (ΔG) of G-quadruplexes is key to understanding their function.
• Differential heat capacity (ΔCP) is vital for describing temperature-dependent thermodynamic properties but has not been directly measured for G-quadruplex unfolding.

Purpose of the Study:

• To directly measure the change in heat capacity (ΔCP) during the unfolding of G-quadruplexes.
• To assess the impact of ΔCP on thermodynamic parameters (ΔH, ΔS, ΔG) of G-quadruplexes.
• To highlight the importance of considering ΔCP in conformational studies of guanine-rich DNA.

Main Methods:

• Differential scanning calorimetry (DSC) was employed to measure ΔCP.
• G-quadruplexes were formed from modified DNA sequences of c-MYC, VEGF, and Bcl-2 oncogene promoter regions.

Main Results:

• The average ΔCP for G-quadruplex unfolding was determined to be 0.49 ± 0.12 kcal mol⁻¹ K⁻¹.
• Disregarding ΔCP introduced substantial errors in extrapolated ΔH and ΔS values.
• Neglecting ΔCP can result in up to 140% relative error in ΔG extrapolated to room temperature.

Conclusions:

• Direct measurement of ΔCP is essential for accurate thermodynamic characterization of G-quadruplexes.
• Accurate thermodynamic data, including ΔCP, is critical for understanding the role of G-quadruplexes in genomic events.
• The study underscores the necessity of incorporating ΔCP into conformational analyses of G-rich DNA structures.