Molecular simulation of adsorption of hydrophobin HFBI to the air-water, DPPC-water and decane-water interfaces

Molecular dynamics simulation has been used to model the adsorption of the class II hydrophibin HFBI from Trichoderma ree s ei at the vacuum-water, DPPC bilayer-water and decane-water interfaces. When two HFBI molecules were simulated in a water-box they self-associated into a dimer with the two hydrophobic patches of the molecule forming the dimer interface. When at the fluid interfaces HFBI adsorbed to both the vacuum-water and decane-water interfaces by adopting a conformation where the hydrophobic patch is parallel to and embedded into the interface. At the DPPC bilayer interface, however, the hydrophobic patch is oriented perpendicular to the interface, although still partially embedded into the bilayer. This difference in adsorbed conformation orientation is most likely due to the presence of the hydrophilic phosphatidyl head groups that are found preferentially at the surface of the bilayer. The degree of tertiary conformational change in the adsorbed HFBI molecules is low at the vacuum-water, slightly greater at the DPPC-water interface, and quite substantial at the decane-water interface. Changes in secondary structure are small, with only HFBI at the decane-water interface showing a significant reduction in beta structure. The effect of the HFBI molecule on the DPPC bilayer is marked, with changes in the ordering of the DPPC molecules being observed not only on the side of the bilayer where the protein is adsorbed, but also on the side opposite to that where the protein adsorbs. The results support the view that hydrophobin molecules behave as rigid janus particles when they adsorb to fluid interfaces.