Can All-Atom Molecular Dynamics Simulations Quantitatively Describe Homeodomain-DNA Binding Equilibria?

Area of Science:

• Computational biology
• Biophysics
• Molecular modeling

Background:

• Protein-DNA interactions are crucial for cellular processes.
• Accurate calculation of binding free energies is essential for drug discovery and understanding biological mechanisms.
• Molecular dynamics (MD) simulations offer a powerful tool for studying these interactions at the atomic level.

Purpose of the Study:

• To evaluate the accuracy of a molecular dynamics (MD) based approach for calculating standard binding free energies of protein-DNA complexes.
• To compare the performance of two modern molecular mechanical force fields in predicting these binding energies.
• To investigate the temperature dependence of binding free energies for different protein-DNA systems.

Main Methods:

• Umbrella sampling simulations were employed to calculate the potential of mean force (PMF).
• Standard binding free energies were extracted from the PMF for two distinct protein-DNA systems.
• Simulations were conducted across a range of temperatures using two contemporary molecular mechanical force fields.

Main Results:

• Calculated standard binding free energies were consistently overestimated when compared to experimental data.
• Significant discrepancies were observed between the two protein-DNA systems and the two force fields, attributed to varying contact formation propensities.
• The number of protein-DNA contacts increased with temperature, aligning with experimental observations of binding enthalpies.

Conclusions:

• The MD-based setup shows potential but requires refinement for accurate prediction of protein-DNA binding free energies.
• Force field selection and protein structural characteristics (disordered vs. globular) critically influence simulation outcomes.
• While trends with temperature were observed, definitive conclusions on the temperature dependence of binding free energies were limited by statistical uncertainty.