A comparison of the surface activity of the fungal hydrophobin SC3p with those of other proteins.

The fungal hydrophobin SC3p, a protein secreted by Schizophyllum commune, has become known to form SDS-insoluble layers and to change the physico-chemical properties of an interface. In this study, the surface activity of SC3p was studied by determining the interfacial tensions gamma iv and gamma sl during adsorption of SC3p at both the liquid-vapour and the solid-liquid interface utilizing the in situ technique axisymmetric drop-shape analysis by profile. To this end, protein solution droplets were put on the solid fluoroethylene-propylene-Teflon. At the liquid-vapour interface, SC3p caused a large decrease of gamma iv from 72 to 43 mJ m-2 at the concentration of 0.1 mg ml-1. At the solid-liquid interface, gamma sl was slightly decreased, whereas the contact angle theta increased, indicating an increase in hydrophobicity of FEP-Teflon, which is unique among the proteins studied so far. Earlier findings indicated a decrease in hydrophobicity of Teflon upon adsorption of SC3p, but this was after a washing and drying step. In order to reconcile these findings with those of the present study, adsorption of SC3p to hydrophobic surfaces is suggested to occur in bilayers. The second layer is supposed to be less strongly adsorbed than the first layer and can be easily removed by washing.