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 structures such as spores and fruiting bodies. These monolayers are extremely resistant to degradation and as such offer the possibility of a range of biotechnological applications involving the reversal of surface polarity. The molecular details underlying the formation of these monolayers, however, have been elusive. We have studied EAS, the hydrophobin from the ascomycete Neurospora crassa, in an effort to understand the structural aspects of hydrophobin polymerization.


RESULTS
We have purified both wild-type and uniformly 15N-labeled EAS from N. crassa conidia, and used a range of physical methods including multidimensional NMR spectroscopy to provide the first high resolution structural information on a member of the hydrophobin family. We have found that EAS is monomeric but mostly unstructured in solution, except for a small region of antiparallel beta sheet that is probably stabilized by four intramolecular disulfide bonds. Polymerised EAS appears to contain substantially higher amounts of beta sheet structure, and shares many properties with amyloid fibers, including a characteristic gold-green birefringence under polarized light in the presence of the dye Congo Red.


CONCLUSIONS
EAS joins an increasing number of proteins that undergo a disorder-->order transition in carrying out their normal function. This report is one of the few examples where an amyloid-like state represents the wild-type 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.
Mackay
J P
JP
Department of Biochemistry, University of Sydney, NSW 2006, Sydney, Australia. j.mackay@biochem.usyd.edu.au
Matthews
J M
JM
Winefield
R D
RD
Mackay
L G
LG
Haverkamp
R G
RG
Templeton
M D
MD
D000595:Amino Acid Sequence; D000682:Amyloid / Q000737:chemistry*; D002942:Circular Dichroism; D004396:Coloring Agents; D003224:Congo Red; D005656:Fungal Proteins / Q000737:chemistry* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D009492:Neurospora crassa / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D020033:Protein Isoforms / Q000737:chemistry / Q000302:isolation & purification; D017433:Protein Structure, Secondary; D012996:Solutions
D000682:Amyloid; D004396:Coloring Agents; D005656:Fungal Proteins; D020033:Protein Isoforms; D012996:Solutions; D003224:Congo Red