STRUCTURAL CHARACTERIZATION OF THE HYDROPHOBIN SC3, AS A MONOMER AND AFTER SELF-ASSEMBLY AT HYDROPHOBIC HYDROPHILIC INTERFACES/

Hydrophobins are small fungal proteins that self-assemble at hydrophil ic/hydrophobic interfaces into amphipathic membranes that, in the case of Class I hydrophobins, can be disassembled only by treatment with a gents like pure trifluoroacetic acid. Here we characterize, by spectro scopic techniques, the structural changes that occur upon assembly at an air/water interface and upon assembly on a hydrophobic solid surfac e, and the influence of deglycosylation on these events. We determined that the hydrophobin SC3 from Schizophyllum commune contains 16-22 O- linked mannose residues, probably attached to the N-terminal part of t he peptide chain. Scanning force microscopy revealed that SC3 adsorbs specifically to a hydrophobic surface and cannot be removed by heating at 100 degrees C in 2% sodium dodecyl sulfate. Attenuated total refle ction Fourier transform infrared spectroscopy and circular dichroism s pectroscopy revealed that the monomeric, water-soluble form of the pro tein is rich in beta-sheet structure and that the amount of beta-sheet is increased after self-assembly on a water-air interface. alpha-Heli x is induced specifically upon assembly of the protein on a hydrophobi c solid. We propose a model for the formation of rodlets, which may be induced by dehydration and a conformational change of the glycosylate d part of the protein, resulting in the formation of an amphipathic al pha-helix that forms an anchor for binding to a substrate. The assembl y in the beta-sheet form seems to be involved in lowering of the surfa ce tension, a potential function of hydrophobins.