Twist-diameter coupling drives DNA twist changes with salt and temperature

Area of Science:

• Biophysics
• Molecular Biology
• Materials Science

Background:

• DNA structure is sensitive to environmental factors such as salt concentration and temperature.
• These DNA deformations are critical for biological functions and material science applications.

Purpose of the Study:

• To investigate the impact of salt concentration on DNA structure, specifically DNA overwinding.
• To elucidate the underlying mechanism of salt-induced DNA twist changes.
• To determine the quantitative relationship between DNA diameter and twist, and predict temperature-dependent twist changes.

Main Methods:

• Magnetic tweezers experiments were employed to observe DNA behavior under varying salt conditions.
• Simulations and theoretical calculations were used to quantitatively explain the observed phenomena.
• The twist-diameter coupling constant was determined experimentally and theoretically.

Main Results:

• Increased concentrations of NaCl, KCl, and RbCl led to significant DNA overwinding.
• A quantitative mechanism was established: enhanced salt screening reduces DNA diameter, inducing twist increase via twist-diameter coupling.
• The twist-diameter coupling constant was determined to be 4.5 ± 0.8 kBT/(degrees∙nm) per base pair.
• Predicted temperature dependence of DNA twist (Δωbp/ΔT ≈ -0.01 degree/°C) aligns with experimental data.

Conclusions:

• Twist-diameter coupling is a key mechanism driving salt-induced DNA overwinding.
• This coupling also explains the temperature dependence of DNA twist.
• The findings highlight a common biophysical principle governing DNA conformational changes in response to environmental stimuli.