Molecular Dynamics Simulation Of Protein Adsorption On Polyethylene Interface

Protein adsorption has widely applied in many areas, such as biomedical, biomaterials, protein separation, drug delivery and so on. Complexity of protein adsorption makes it impossible to understand its mechanism completely and exactly. Molecular dynamics can study protein adsorption at the molecular level and get information that the experiment can't. PE is a simple and widely used polymer. It is widely applied in biomedical material, artificial joint for example. In present paper, molecular dynamics simulations were performed to study the adsorption of ploy-ten-lysine, bovine pancreatic trypsin inhibitor and human lysozyme on PE surface with GROMACS software, and effects of some conditions (interface morphology, side chain charge, water model, force field, the distance between protein and interface) on adsorption process were studied.Steepest descent integrator was used to minimize energy of protein initial structure under periodic boundary conditions in rectangular box. MD simulations were performed using leapfrog integrator in NVT ensemble. For the calculation of nonbonded interactions, cutoffs and PME algorithms were used. Conformation changes in adsorption were described by dihedral changes and Ramachandran plots distribution. Radius of gyration, accessible surface area of proteins and interaction energy between protein and PE surface were analyzed in adsorption process.Results indicate that interaction between ploy-ten-lysine with full side chain charges and PE surface is stronger than ploy-ten-lysine without side chain charge. The interaction between random polyethylene interface and poly-ten-lysine is stronger than regular polyethylene interface. Water molecules have great effects on protein adsorption process through hydrogen bonds.MD simulations also showed that selection of water models and force field has impacts on simulation results. The interaction between ploy-ten-lysine and PE surface is strongest with SPC water model. The interaction between ploy-ten-lysine and PE under AMBER94 force field is stronger than under GROMACS.Conformation analysis found that molecular conformations of protein change in adsorption process.α-helix in ploy-ten-lysine were almost completely disappeared. The partial loss ofβ-sheets in bovine pancreatic trypsin inhibitor was founded, and α-helix also lost partially in human lysozyme.Energy analysis revealed that van der Waals interaction between PE interface and proteins is the main driving force of protein adsorption.