DNA stretching and compression: large-scale simulations of double helical structures

Area of Science:

• Structural biology
• Computational biophysics
• Molecular modeling

Background:

• DNA exists in canonical forms (A, B) but can adopt non-canonical structures under stress.
• Understanding DNA's mechanical properties is crucial for processes like DNA replication and repair.

Purpose of the Study:

• To investigate the conformational landscape of DNA under extreme stretching and compression using all-atom potential energy studies.
• To identify and characterize high-energy, "activated" DNA structures and their relevance to biological functions.

Main Methods:

• All-atom potential energy calculations on poly(dG).poly(dC) and poly(dA).poly(dT) double helices.
• Simulating DNA structures from compressed states (2.0 Å/bp) to highly extended forms (7.0 Å/bp).
• Analyzing changes in base-pair orientation, backbone conformation, and helical parameters (Rise, Twist, Roll, Slide).

Main Results:

• Identification of four distinct hyperfamilies of right-handed DNA structures beyond canonical forms.
• Canonical A- and B-DNA forms represent the lowest energy states.
• Unusual helical conformations become energetically favorable under significant stretching or compression.
• DNA can be stretched twofold or compressed by half before significant energy increase, correlating with experimental observations.

Conclusions:

• DNA's conformational flexibility under mechanical stress is key to its biological functions.
• Calculated "activated" DNA forms provide a stereochemical model for protein-DNA recognition in recombination and transcription.
• Compressed DNA structures resemble those found in complexes with TATA-box binding protein (TBP), explaining groove accessibility.