Molecular Dynamics Simulation of β-Lactoglobulin at Different Oil/Water Interfaces

Controlling and manipulating protein behavior at an interface is of immense relevance to a broad range of physicochemical and biological phenomena and technological processes. Although many experimental studies have contributed to rapid progress in the fundamental knowledge of protein behavior at interfaces, detailed molecular-level understanding of the mechanism of protein adsorption at an interface is still remarkably lacking. In this study, atomistic molecular dynamics simulations were used to characterize the adsorption of β-lactoglobulin at two different oil/water (O/W) interfaces, where the oil was either the marginally hydrophilic octanol or the more hydrophilic triolein, and the results were compared to those of a previous study utilizing the hydrophobic oil decane. Both the approach to the surface and the mechanism of adsorption depend upon the hydrophilicity of the oil and the interfacial tension of the O/W interface, with the nature of the adsorption, the accompanying structural changes, and the energetic driving force differing markedly between the different oils. Intriguingly, the behavior of the protein resembles that predicted for a soft spherical particle at an O/W interface. The results are also in agreement with key experimental findings, particularly the observation that proteins undergo more conformational change upon adsorption to hydrophobic surfaces, flattening out to expose hydrophobic interior residues to the surface, and that a thicker layer of native-like adsorbed protein forms at hydrophilic surfaces, and reveal structural and mechanistic detail behind each mechanism of adsorption.