Water structure around enkephalin near a GeO₂ surface: a molecular dynamics study

A molecular model was created consisting of leucine enkephalin (a pentapeptide protein) near a germanium dioxide (GeO₂) surface surrounded by water molecules. A molecular dynamic (MD) simulation of the system was conducted, and forces exerted by the water on both the surface and the protein were calculated. Orientational and spatial distribution functions of the water were calculated and were examined to determine if structured water existed and how it contributed to the intermolecular forces. Results from the study demonstrated that there is a strong spatial and orientational structuring of water near the GeO₂ surface and that it is dependent on the proximity of the protein to the surface. Only minimal structuring occurred near the protein. A linear correlation was observed between the force of water on the protein and the angular distribution of water molecules in the region with the highest spatial density. When the protein is oriented with its polar side toward the GeO₂ surface, the water structure near the protein disrupts the typical structure of the water near the surface, causing a force that pushes the protein away from the surface. When the protein is oriented with its non-polar side toward the surface, there is only minimal disruption of the typical water structure, and the resulting net forces between surface and protein are attractive.