Forces between Hydrophilic Surfaces Adsorbed with Apolipoprotein AII Alpha Helices

To provide better understanding of how a protein secondary structure affects protein−protein and protein−surface interactions, forces between amphiphilic α-helical proteins (human apolipoprotein AII) adsorbed on a hydrophilic surface (mica) were measured using an interferometric surface force apparatus (SFA). Forces between surfaces with adsorbed layers of this protein are mainly composed of electrostatic double layer forces at large surface distances and of steric repulsive forces at small distances. We suggest that the amphiphilicity of the α-helix structure facilitates the formation of protein multilayers next to the mica surfaces. We found that protein−surface interaction is stronger than protein−protein interaction, probably due to the high negative charge density of the mica surface and the high positive charge of the protein at our experimental conditions. Ellipsometry was used to follow the adsorption kinetics of this protein on hydrophilic silica, and we observed that the adsorption rate is not o...