Self-Assembly and Conformational Changes of Hydrophobin Classes at the Air−Water Interface

We use surface-specific vibrational sum-frequency generation spectroscopy (VSFG) to study the structure and self-assembling mechanism of the class I hydrophobin SC3 from Schizophyllum commune and the class II hydrophobin HFBI from Trichoderma reesei. We find that both hydrophobins readily accumulate at the water−air interface and form rigid, highly ordered protein films that give rise to prominent VSFG signals. We identify several resonances that are associated with β-sheet structures and assign them to the central β-barrel core present in both proteins. Differences between the hydrophobin classes are observed in their interfacial self-assembly. For HFBI, we observe no changes in conformation upon adsorption to the water surface. For SC3, we observe an increase in β-sheet-specific signals that supports a surface-driven self-assembly mechanism in which the central β-barrel remains intact and stacks into a larger-scale architecture, amyloid-like rodlets.