Molecular dynamics simulations of hen egg white lysozyme adsorption at a charged solid surface.

Hen egg white lysozyme (HEWL) adsorption on negatively charged, hydrophilic surfaces has been investigated using atomistic molecular dynamics. Analysis of six 20 ns trajectories performed at pH 7 and ionic strength 0.02 M (NaCl) reveals that conformational alterations are required for HEWL adsorption, and that upon adsorption the protein loses some alpha-helical content. Simulations for a few different initial orientations show that the HEWL protein adsorbs on a flat surface with an angle between the protein long axis and the surface of about 45 degrees . The main adsorption site is located on the N,C-terminal part of the HEWL surface; the major role is played by Lys1, Arg5, Arg14, and Arg128. Adsorption is not found with contrary orientations. Two additional 20 ns trajectories calculated with 0.5 M ionic strength suggest that the main force governing adsorption is electrostatic attraction between parts of the protein and the surface. A trajectory obtained for the protein situated inside a cubic box built from the charged surfaces shows that the adsorption pattern is different for flat and nonflat surfaces, and in particular, adsorption on the nonflat surface requires tertiary structure alterations and partial unfolding. The observed trends are consistent with both experimental and previous computational studies.