Hydrophobins are surface-active proteins that form a hydrophobic, water-repelling film around aerial fungal structures. They have a compact, particle-like structure, in which hydrophilic and hydrophobic regions are spatially separated. This surface property renders them amphiphilic and is reminiscent of synthetic Janus particles. Here we report surface-specific chiral and non-chiral vibrational sum-frequency generation spectroscopy (VSFG) measurements of hydrophobins adsorbed to their natural place of action, the air-water interface. We observe that hydrophobin molecules undergo a reversible change in orientation (tilt) at the interface when the pH is varied. We explain this local orientation toggle from the modification of the inter-protein interactions and the interaction of hydrophobin with the water solvent, following the pH-induced change of the charge state of particular amino acids.

J. Phys. Chem. Lett.
Ultrafast Spectroscopy

Meister, K, Roeters, S.J, Paananen, A, Woutersen, S, Versluis, J, Szilvay, G.R, & Bakker, H.J. (2017). Observation of PH-Induced Protein Reorientation at the Water Surface. J. Phys. Chem. Lett., 8(8). doi:10.1021/acs.jpclett.7b00394