Aqueous Amino Acids and Proteins Near the Surface of Gold in Hydrophilic and Hydrophobic Force Fields

TL;DR

This study uses molecular dynamics simulations to compare how amino acids and proteins interact with gold surfaces under different force fields, revealing that water properties and binding behaviors vary significantly with surface hydrophobicity.

Contribution

It provides a detailed comparison of amino acid and protein interactions with gold surfaces using multiple force fields, highlighting the impact of surface hydrophilicity on binding and water structure.

Findings

Binding energies differ from sum of individual amino acids.

Hydrophobic surfaces favor protein adsorption via strong amino acid binding.

Water structure near the surface varies with the force field used.

Abstract

We calculate potentials of the mean force for twenty amino acids in the vicinity of the (111) surface of gold, for several dipeptides, and for some analogs of the side chains, using molecular dynamics simulations and the umbrella sampling method. We compare results obtained within three different force fields: one hydrophobic (for a contaminated surface) and two hydrophilic. All of these fields lead to good binding with very different specificities and different patterns in the density and polarization of water. The covalent bond with the sulfur atom on cysteine is modeled by the Morse potential. We demonstrate that binding energies of dipeptides are different than the combined binding energies of their amino-acidic components. For the hydrophobic gold, adsorption events of a small protein are driven by attraction to the strongest binding amino acids. This is not so in the hydrophilic cases - a result of smaller specificities combined with the difficulty for proteins, but not for single amino acids, to penetrate the first layer of water. The properties of water near the surface sensitively depend on the force field.