WATER-STRUCTURE AROUND ENKEPHALIN NEAR A PE SURFACE - A MOLECULAR-DYNAMICS STUDY

A molecular model was constructed simulating a pentapeptide protein, l eucine enkephalin, near a crystalline polyethylene (PE) surface surrou nded by explicit water molecules. A molecular dynamic simulation of th e model was performed to examine the forces exerted on the protein by the surface and the water molecules. The orientational distribution fu nctions of the water molecules were examined to determine if and how s tructured or ordered water in the model contributed to the attractive and repulsive forces between the protein and the surface. The results of the simulations showed that there is relatively strong spatial and orientational structuring of the water adjacent to the PE surface, and a lesser amount of structuring near the protein. The distribution is a function of the orientation of the protein with respect to the surfa ce. The proximity of the protein to the surface has a strong influence on the density and structure of water between the protein and surface . A linear correlation between the force of water on the protein and t he angular distribution of water molecules was observed in the most de nse region of water between the protein and surface. When the protein presents its polar side toward the nonpolar PE surface, the water stru cture near the protein disrupts the normal structure of water near the surface. Additionally, the orientational structure of the water betwe en them causes an asymmetric force on the protein, pushing it away fro m the surface. When the nonpolar side of the protein is presented towa rd the PE, there is less disruption of water structure, and the intera ction forces are attractive. (C) 1998 Academic Press.