Overtwisting induces polygonal shapes in bent DNA.

Area of Science:

• Biophysics
• Computational Biology
• Molecular Biology

Background:

• DNA minicircles are circular DNA molecules crucial in various biological processes.
• Understanding their structural properties under torsional stress is essential for molecular biology.
• Twist-bend coupling is a recently identified DNA property influencing its mechanics.

Purpose of the Study:

• To investigate the minimal energy shapes of torsionally constrained DNA minicircles.
• To analyze the impact of twist-bend coupling on DNA minicircle conformation.
• To determine how twist and bending energies are affected by renormalized stiffness constants.

Main Methods:

• Combining analytical results with simulations of coarse-grained DNA models.
• Imposing torsional constraints (over or undertwist) on DNA minicircles.
• Analyzing the resulting minimal energy shapes and energy contributions.

Main Results:

• Twist-bend coupling induces periodic alternations of high and low curvature, forming rounded polygon shapes.
• These shapes resemble rounded polygons due to the interplay of twist and bend.
• Twist and bending energies are governed by renormalized stiffness constants, not bare ones.

Conclusions:

• The study reveals novel minimal energy shapes for DNA minicircles under torsional stress.
• Twist-bend coupling significantly influences DNA minicircle conformation and energy landscapes.
• Findings have implications for interpreting experiments aimed at determining DNA elastic constants.