Effect of surfactants on surface-induced denaturation of proteins: evidence of an orientation-dependent mechanism

When proteins bind to interfaces, the resulting changes in protein structure can lead to loss of protein function. We investigate the mechanism by which surfactant molecules can counteract surface-induced protein denaturation through a detailed study of the stability of the GB1 peptide at the air-water, ice-water, and silica-water interfaces using molecular dynamics simulations coupled with metadynamics. Our simulations reveal that the air-water interface and, to a lesser extent, the ice-water interface destabilize the protein by direct interactions between the protein and surface that disrupt the hydrophobic core of the protein, while the weakly interacting silica surface stabilizes the protein through confinement effects. Addition of the surfactant Tween 80 leads to stabilization of the protein at the air-water and ice-water surfaces and mild destabilization at the water-silica interface. We show that the amphiphilic nature of the surfactant is key to its stabilizing/destabilizing effect, with an orientation-dependent mechanism in which the protein is stabilized when the hydrophilic heads of the surfactant point toward the protein.