Electrostatics of nucleic acid folding under conformational constraint

Area of Science:

• Biophysics
• Molecular Biology
• Physical Chemistry

Background:

• Nucleic acid folding is influenced by ion atmospheres, which are complex to study.
• Existing theories struggle with the conformational diversity of unfolded nucleic acids.

Purpose of the Study:

• To investigate the impact of ion concentration and identity on DNA hairpin stability.
• To provide benchmark data for improving electrostatic theories of nucleic acid folding.

Main Methods:

• Utilized a single-molecule optical trapping assay to measure DNA hairpin unfolding equilibrium.
• Constrained unfolded states to limited conformations to simplify theoretical treatment.

Main Results:

• DNA hairpin stability increased linearly with the logarithm of monovalent cation concentration.
• Smaller monovalent cations favored the folded state.
• Magnesium ions (Mg2+) showed significantly greater stabilization than monovalent cations at low concentrations.

Conclusions:

• Poisson-Boltzmann theory accurately predicted stability for monovalent cations but failed for Mg2+.
• Discrepancies suggest ion-ion correlation effects are crucial for multivalent cations.
• The study provides high-resolution data crucial for developing advanced electrostatic theories for nucleic acid folding.