Explicit ions/implicit water generalized Born model for nucleic acids.

Area of Science:

• Computational Chemistry
• Biophysics
• Molecular Modeling

Background:

• The behavior of ions around highly charged nucleic acids is crucial for their structure and function.
• Accurate modeling of ion-nucleic acid interactions requires sophisticated computational approaches.
• Existing implicit solvent models often struggle to capture the nuances of explicit ion behavior.

Purpose of the Study:

• To develop and validate a novel explicit ions/implicit water model for simulating nucleic acid systems.
• To investigate the distribution and interaction of monovalent and trivalent ions with DNA and RNA duplexes.
• To explore the physical basis of ion-thymine interactions and their role in DNA condensation.

Main Methods:

• Development of a modified generalized Born (GB) model incorporating explicit ions and an implicit solvent.
• Analytical description of charge-charge interactions within the modified GB framework.
• Monte Carlo (MC) simulations of ion-DNA/RNA interactions and potential of mean force calculations.

Main Results:

• The model accurately reproduces monovalent (Na+) and trivalent (CoHex3+) counterion distributions compared to all-atom simulations.
• Subtle differences in CoHex3+ binding between DNA and RNA duplexes (major groove vs. backbone surface) were resolved.
• Ion desolvation penalty near methyl groups of thymine bases significantly influences CoHex3+-thymine interactions.

Conclusions:

• The explicit ions/implicit water GB model provides a computationally efficient and accurate method for studying ion-nucleic acid interactions.
• The model elucidates the molecular basis for differential ion binding and condensation propensities in DNA and RNA.
• Understanding ion-desolvation effects is critical for predicting methylation-induced changes in DNA condensation.