Fungal Fibrils: Application of the Amyloid Polymer Structure by Fungi - The Functional Fold: Amyloid Structures in Nature - page 38

A different line of investigation led to the identification of
hydrophobins as the putative product of genes that are abundantly
expressed at certain stages in fungal development.

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In 1984,
Wessels and colleagues reported high levels of novel mRNAs
expressed during the growth of aerial hyphae and fruiting bodies
in These mRNAs encoded a family of

low molecular weight, hydrophobic proteins which they termed
“hydrophobins”.

Schizophyllum commune.

15

The realization that rodlets were composed of
hydrophobins came when it was demonstrated that solubilization
of the rodlet layers from the cell walls of aerial hyphae or fruiting
bodies by treatment with formic or trifluoroacetic acid generated
the monomeric forms of the hydrophobins SC3 and SC4, respectively.
The discovery that rodlet layers could be solubilized by these acids
paved the way for the analysis of rodlet proteins from a number of
fungi. It was also found that the hydrophobin proteins were secreted
into the culture medium in a monomeric form, but that agitation of
the solution rapidly converted the protein into a sodium dodecyl
sulfate (SDS)-insoluble aggregate.

16

Soon after, the hydrophobin EAS
(protein encoded by the easily wettable gene) from

17

N. crassa and

18

RodA, the hydrophobin protein from were

cloned and shown to encode proteins that were clearly homologous
to the hydrophobins of

Aspergillus nidulans ,

It was subsequently shown that
disruption of the former gave rise to the “easily wettable phenotype”
in

S. commune.

N. crassa (Fig. 3.1c) that had been described by Seletrennikoff

19

earlier, and disruption of RodA in A. nidulans gave rise to non-

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hydrophobic spores that lacked rodlets. Furthermore, the purified

N. crassa rodlet layer, solubilized by trifluoroacetic acid, was shown

to be the proteolytically cleaved product of

. In addition, sequence
comparison identified putative hydrophobin proteins in several
other organisms, including the insect pathogenic fungus

eas

Metharizium

20 21

anisopliae , the rice blast fungus Magnaporthe grisea , and

22

Ophiostomi ulmi A recent

search of the NCBI nr database found 128 different hydrophobin
sequences.

, the causative agent of Dutch elm disease.

23

Whole genome sequencing projects have now revealed
that hydrophobins exist in fungi as small gene families of between 2
(

N. crassa ) and 24 ( Coprinus cinereus ) members (http://www.broad.

mit.edu/annotation/fgi/).