The dynamics of proton transfer between adjacent sites

Area of Science:

• Biophysics
• Computational Chemistry
• Biochemistry

Background:

• Proton transfer is crucial in biology but difficult to model at the atomic level due to quantum effects and electrostatic interactions.
• Protein-water dielectric boundaries significantly modulate local electrostatic potentials, complicating reaction modeling.

Purpose of the Study:

• To investigate ion diffusion and interactions at a protein surface using molecular dynamics simulations.
• To understand the influence of local electrostatic fields on ion behavior and transfer mechanisms.

Main Methods:

• Molecular dynamics simulations were performed on a model protein (S6 of the bacterial ribosome) with diffusing Na+ and Cl- ions.
• Analysis focused on ion trajectories, residence times, and interactions with attractor residues.

Main Results:

• A 'detained state' was identified where ions remain near specific residues due to the local electrostatic field.
• Ions in the detained state exhibit reduced diffusion but can transfer between nearby attractors.
• This ion transfer mechanism resembles proton collecting antennas in proton proteins.

Conclusions:

• The local electrostatic field plays a critical role in modulating ion behavior at protein interfaces.
• The observed ion transfer mechanism provides insights into biological proton transfer processes.
• Computational modeling, like molecular dynamics, is valuable for studying complex interfacial reactions.