Essential Considerations for Free Energy Calculations of RNA-Small Molecule Complexes: Lessons from the...

Area of Science:

• Computational Chemistry
• Molecular Modeling
• Drug Discovery

Background:

• Alchemical free energy calculations are standard for protein-ligand binding affinity prediction.
• Application to RNA targets remains less explored, necessitating investigation into specific modeling requirements.
• Understanding RNA-ligand interactions is vital for developing novel therapeutics.

Purpose of the Study:

• To evaluate the performance of absolute binding free energy calculations for RNA targets.
• To identify key modeling considerations impacting RNA-ligand binding predictions.
• To establish best practices for RNA-ligand free energy calculations.

Main Methods:

• Systematic investigation of modeling decisions for a theophylline-RNA aptamer system.
• Exploration of magnesium ion placement strategies and RNA backbone restraints.
• Assessment of buffer condition, force field, and water model impacts on prediction accuracy.

Main Results:

• Magnesium ion placement significantly affects binding affinity predictions.
• RNA backbone restraints provide accurate predictions, especially when Mg2+ information is unavailable.
• Accurate modeling of buffer conditions (salt type, ionic strength) is essential.
• Achieved high accuracy with MAE = 2.2 kcal/mol, R = 0.9, Kendall's τ = 0.7 when optimizing parameters.

Conclusions:

• Absolute free energy calculations can accurately predict RNA-ligand binding affinity with careful modeling.
• Magnesium ion handling and buffer condition simulation are critical for RNA systems.
• This study provides foundational insights and practical advice for applying these methods to RNA targets.