Self-assembled bilayers from the protein HFBII hydrophobin: Nature of the adhesion energy

The hydrophobins are a class of amphiphilic proteins which spontaneously adsorb at the air/water interface and form elastic membranes of high mechanical strength as compared to other proteins. The mechanism of hydrophobin adhesion is of interest for fungal biology and for various applications in electronics, medicine, and food industry. We established that the drainage of free foam films formed from HFBII hydrophobin solutions ends with the appearance of a 6 nm thick film, which consists of two layers of protein molecules, that is, it is a self-assembled bilayer (S-bilayer), with hydrophilic domains pointing inward and hydrophobic domains pointing outward. Its formation is accompanied by a considerable energy gain, which is much greater than that typically observed with free liquid films. The experiments at different pH show that this attraction between the "hydrophilic" parts of the HFBII molecules is dominated by the short-range hydrophobic interaction rather than by the patch-charge electrostatic attraction.