Charged Small Molecule Binding to Membranes in MD Simulations Evaluated against NMR Experiments

Area of Science:

• Biophysics
• Computational Chemistry
• Molecular Modeling

Background:

• Interactions between charged molecules and biomembranes are crucial for biological functions.
• Accurately modeling these interactions is challenging due to experimental difficulties and theoretical limitations.
• Standard molecular dynamics (MD) simulations often overestimate cation binding to lipid bilayers, questioning force field accuracy.

Purpose of the Study:

• To evaluate the binding affinities of charged small molecules (etidocaine, tetraphenylphosphonium) to a POPC lipid bilayer using MD simulations.
• To investigate the influence of electronic polarizability on the binding of these molecules.
• To compare the binding behavior of charged small molecules with that of monoatomic ions like sodium and calcium.

Main Methods:

• Classical molecular dynamics (MD) simulations were employed.
• The binding was assessed by analyzing changes in lipid head-group order parameters.
• The study considered standard force field parameters and the implicit inclusion of electronic polarizability.

Main Results:

• Charged small molecules exhibited different binding behavior compared to sodium and calcium ions.
• Their binding affinities were not overestimated by standard force field parameters.
• Electronic polarizability enhanced their binding affinity, and they penetrated the hydrophobic membrane core.
• Binding is driven by hydrophobic effects for these molecules, contrasting with electrostatic interactions for monoatomic ions.

Conclusions:

• Charged small molecules and monoatomic ions interact with lipid bilayers via distinct mechanisms.
• MD simulations require refined force fields and methodologies to accurately capture these diverse interactions.
• The findings provide insights for developing improved simulation parameters for biomembrane-molecule interactions.