The Pleurotus ostreatus hydrophobin Vmh2 and its interaction with glucans

Hydrophobins are small self-assembling proteins, produced by fungi. A Class I hydrophobin secreted by the basidiomycete fungus Pleurotus ostreatus was purified and identified. The pure protein is not water soluble, whereas complexes formed between the protein and glycans, produced in culture broth containing amylose, are soluble in water. Glycan structure matched to cyclic structures of α-(1-4) linked glucose containing from six to sixteen monomers (cyclodextrins). Moreover it was verified that not only pure cyclodextrins, but also a linear oligosaccharide and even the simple glucose monomer are able to solubilise the hydrophobin in water. The aqueous solution of the protein -in the presence of the cyclic glucans- showed propensity to self-assembly and conformational changes towards beta-structure were observed on vortexing the solution. On the other hand the pure protein dissolved in less polar solvent (60% ethanol) is not prone to self assembly and no conformational change was observed. When the pure protein was deposited on a hydrophobic surface, it formed a very stable biofilm whose thickness was about 3nm, whereas the biofilm was not detected on a hydrophilic surface. When the water-soluble protein -in the presence of the cyclic glucans- was used, thicker (up to ten fold) biofilms were obtained either on hydrophilic and hydrophobic surfaces.