Interfacial self-assembly of a Schizophyllum commune hydrophobin into an insoluble amphipathic protein membrane depends on surface hydrophobicity

Abstract

Hydrophobins are small secreted fungal proteins rich in hydrophobic amino acids with a characteristic hydropathy pattern and conserved location of eight cysteine residues. It was previously shown that purified SC3p hydrophobin of Schizophyllum commune self-assembles at hydrophilic/hydrophobic interfaces into a sodium dodecyl sulphate (SDS)-insoluble amphipathic protein membrane typified at the hydrophobic side by a mosaic of parallel rodlets, similar to those seen at the hydrophobic surface of aerial hyphae of this fungus. Here we show the assembly of SC3p at the interface between water and a continuous hydrophobicity gradient surface obtained by coating glass with dichlorodimethylsilane and displaying contact angles of water ranging from 20° up to 107°. The amount of assembled SC3p (defined as SC3p becoming insoluble in hot SDS) sharply increased in the region of the gradient surface displaying advancing water contact angles between 60° and 90° and then more slowly towards the 107° region, i.e. the hydrophobic end. Here, the adsorbed SC3p decreases the advancing water contact angle from 107° on the bare gradient surface to 60° on the protein coated surface (to 39° before extraction with SDS). The SDS-insoluble SC3p was removed by trifluoroacetic acid, which is known to dissociate assembled hydrophobins, hence restoring the wettability characteristics close to those of the original hydrophobicity gradient surface. Since fungal hyphae firmly attach to natural surfaces which are often hydrophobic, these results suggest a role for hydrophobins in fungal pathogenicity and other fungal host interactions.