Activation volume of DNA duplex formation

Area of Science:

• Biophysics
• Molecular Biology
• Chemical Kinetics

Background:

• Understanding DNA duplex stability and kinetics is crucial for molecular biology and drug design.
• The helix-coil equilibrium governs DNA structural transitions, influencing biological processes.
• Fractional guanine-cytosine (G x C) content impacts DNA duplex stability and dynamics.

Purpose of the Study:

• To investigate the kinetics of helix-coil equilibrium in homopurine-homopyrimidine DNA duplexes.
• To determine the effect of fractional G x C content on reaction rate constants and activation volumes.
• To elucidate the influence of hydrostatic pressure on DNA duplex formation and dissociation kinetics.

Main Methods:

• Denaturation-renaturation thermal hysteresis was employed to study DNA kinetics.
• Experiments were conducted on four 22-base pair oligonucleotides with varying f(G x C) (0.14–0.5).
• Hydrostatic pressures up to 200 MPa were applied in 20 mM NaCl and 20 mM Tris-HCl at pH 7.0.

Main Results:

• A two-state bimolecular reaction mechanism adequately described the observed kinetics.
• Increasing f(G x C) from 0.14 to 0.5 significantly increased helix formation rate (k1) and decreased strand separation rate (k(-1)).
• Pressure effects on rate constants were quantified by activation volumes, showing significant differences based on f(G x C).

Conclusions:

• The kinetics of DNA helix formation are strongly influenced by G x C content and hydrostatic pressure.
• Activation volumes for helix formation and strand separation vary with G x C content, providing insights into the reaction mechanisms.
• Extrapolation suggests a near-zero molar volume change for G x C base pair formation in these sequences.