Improved model of hydrated calcium ion for molecular dynamics simulations using classical biomolecular force fields

Area of Science:

• Computational Biology and Biophysics
• Biomolecular Simulations
• Ion Modeling

Background:

• Calcium ions (Ca2+) are crucial for biological processes like cell signaling and brain function.
• Molecular dynamics (MD) simulations are used to study Ca2+ interactions, but standard force field models require validation.
• Existing Ca2+ models in popular force fields (AMBER, CHARMM) have not been rigorously tested for accuracy.

Purpose of the Study:

• To rigorously assess the accuracy of Ca2+ models from AMBER and CHARMM force fields.
• To investigate the performance of standard Ca2+ models in simulating osmotic pressure and DNA-DNA interactions.
• To develop and validate an improved Ca2+ model for accurate biomolecular simulations.

Main Methods:

• Computed osmotic pressure of model Ca2+ compounds (CaCl2, CaAc2) using AMBER and CHARMM force fields.
• Calculated free energy of DNA-DNA interactions using standard and custom Ca2+ models.
• Simulated Ca2+-DNA interactions and electric field-driven DNA translocation through nanopores.

Main Results:

• Standard Ca2+ models inaccurately predicted low osmotic pressures and formed artificial ion clusters.
• Simulations with standard models showed artificial inter-DNA attraction, contradicting experimental repulsion.
• A custom-developed hydrated Ca2+ model yielded results in quantitative agreement with experimental data.

Conclusions:

• Standard Ca2+ force field models exhibit significant inaccuracies, leading to erroneous biological insights.
• The developed custom Ca2+ model accurately reproduces experimental observations for osmotic pressure and DNA interactions.
• The improved Ca2+ model is applicable to diverse MD simulations of biomolecular systems, including nucleic acids, proteins, and membranes.