(723c) Molecular Simulation of Proteins at Interfaces

Protein adsorption plays an important role not only in a wide range of basic biological processes but also in many applications such as protein chromatography, drug delivery on solid substrates, biosensors, biofuel cells and biomaterials. For these processes and applications, one key issue is the orientation of adsorbed proteins on surfaces. Controlled antibody adsorption orientation on surfaces is necessary to ensure that their active sites are away from the surface and accessible to bulk solution for immunoassay applications. For biofuel cell applications, to enable fast ET, adsorbed cytochrome c should have an orientation with the heme ring close and perpendicular to surfaces. Another key issue that determines the activity of adsorbed proteins is their conformation (i.e., how the conformation of the adsorbed protein resembles that of its native state). In this talk, the protein orientation and conformation on charged surfaces are investigated by a hierarchical approach, i.e., studied by colloidal, coarse-grained and all-atom models. Parallel tempering Monte Carlo and molecular dynamics simulations are used. Effects of surface charge density and sign, and solution ionic strength are examined in our simulations. Simulation results show that van der Waals and electrostatic interactions codetermine the orientation of adsorbed proteins. It is found that the electric dipole and hydrophobic dipole of adsorbed proteins play important roles in determining the protein orientation on charged and hydrophobic surfaces.