The hydrophobin EAS is largely unstructured in solution and functions by forming amyloid-like structures

Background: Fungal hydrophobin proteins have the remarkable ability to self -assemble into polymeric, amphipathic monolayers on the surface of aerial s tructures such as spores and fruiting bodies. These monolayers are extremel y resistant to degradation and as such offer the possibility of a range of biotechnological applications involving the reversal of surface polarity. T he molecular details underlying the formation of these monolayers, however, have been elusive. We have studied EAS, the hydrophobin from the ascomycet e Neurospora crassa, in an effort to understand the structural aspects of h ydrophobin polymerization. Results: We have purified both wild-type and uniformly N-15-labeled EAS fro m N. crassa conidia, and used a range of physical methods including multidi mensional NMR spectroscopy to provide the first high resolution structural information on a member of the hydrophobin family. We have found that EAS i s monomeric but mostly unstructured in solution, except for a small region of antiparallel beta sheet that is probably stabilized by four intramolecul ar disulfide bonds. Polymerised EAS appears to contain substantially higher amounts of P sheet structure, and shares many properties with amyloid fibe rs, including a characteristic gold-green birefringence under polarized lig ht in the presence of the dye Congo Red. Conclusions: EAS joins an increasing number of proteins that undergo a diso rder-order transition in carrying out their normal function. This report is one of the few examples where an amyloid-like state represents the wild-ty pe functional form. Thus the mechanism of amyloid formation, now thought to be a general property of polypeptide chains, has actually been applied in nature to form these remarkable structures.