Transitions of Double-Stranded DNA Between the A- and B-Forms

Area of Science:

• Biophysics
• Structural Biology
• Computational Biology

Background:

• Double-stranded DNA (dsDNA) exists in various conformations, notably B-DNA under physiological conditions and A-DNA under low water activity.
• A-DNA can be locally induced in protein-DNA complexes, and B-DNA/A-DNA transitions are implicated in viral genome packaging.

Purpose of the Study:

• To investigate the A-DNA to B-DNA transition dynamics in solution using molecular dynamics (MD) simulations.
• To introduce and utilize the A-B Index (ABI) for quantifying DNA conformational changes along the A-B continuum.

Main Methods:

• Analysis of existing B-DNA MD simulations and new MD simulations of the A-DNA to B-DNA transition.
• Development and application of the A-B Index (ABI) to measure DNA conformation.
• Characterization of the A/B junction in dsDNA using MD simulations.

Main Results:

• The transition from A-DNA to B-DNA in solution at physiological ionic strength occurs rapidly (within 5 ns) with no observed energy barrier.
• More A-phobic DNA sequences exhibit faster transition rates.
• The A/B junction displays an average bend angle of 20-30° with fluctuations occurring on a ~10 ns timescale.

Conclusions:

• dsDNA undergoes spontaneous and rapid transitions from A-DNA to B-DNA in solution.
• Sequence-specific properties, like A-phobicity, significantly affect the kinetics of DNA conformational changes.
• The A/B junction is a structurally characterized feature with dynamic bending properties relevant to DNA conformational flexibility.