Salt dependence of DNA structural stabilities in solution. Theoretical predictions versus experiments

Area of Science:

• Biophysics
• Molecular Biology
• Computational Chemistry

Background:

• DNA exists in various conformations (A, B, Z-DNA) influenced by environmental factors like salt concentration.
• Understanding the energetic contributions of ionic clouds to DNA stability is crucial for predicting these conformational changes.
• Existing theories, including Manning's counterion condensation (CC) and Poisson-Boltzmann (PB) approximations, have limitations in explaining salt-induced transitions.

Purpose of the Study:

• To evaluate the predictive accuracy of different theoretical models for DNA conformational stability.
• To compare the predictions of counterion condensation (CC), Poisson-Boltzmann (PB), and potentials of mean force (PMF) theories against experimental data.
• To determine which theory best explains salt-induced B-Z and B-A DNA transitions.

Main Methods:

• Theoretical comparison of three models: Manning's CC, idealized PB, and Soumpasis' PMF.
• Analysis of theoretical predictions against experimental data for B-Z and B-A DNA transitions.
• Assessment of the dependence of relative DNA form stabilities on monovalent salt concentration.

Main Results:

• The potentials of mean force (PMF) approach provides satisfactory quantitative agreement with experimental data for salt-induced B-Z and B-A transitions.
• The Poisson-Boltzmann (PB) theory qualitatively predicts the B-DNA form to be more favorable at low salt concentrations.
• Manning's counterion condensation (CC) theory inaccurately predicts Z-DNA stability at low salt concentrations and contradicts experimental findings regarding low-salt Z-B transitions.

Conclusions:

• The potentials of mean force (PMF) theory is currently the most accurate model for predicting DNA conformational stability concerning salt-induced transitions.
• The Poisson-Boltzmann (PB) and counterion condensation (CC) theories require refinement to accurately capture the electrostatic contributions to DNA stability and transitions.
• Accurate theoretical treatment of DNA-diffuse ionic cloud free energy is essential for understanding DNA structure and function.