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approximately 110 ° to 32 ° . A similar effect can be observed for EAS
monolayers (Fig. 3.3). Both Class I and Class II hydrophobins are
extremely surface active, that is, they are able to reduce the surface
tension of solutions to which they are added. For example, SC3
from
, and the Class II hydrophobin cryparin from the
causal agent of chestnut blight,
S. commune
Cryphonectria parasitica
, are able to
lower the water surface tension
. The ability
of hydrophobins to reduce water surface tension is thought to play
a functional role in some fungal systems, where hydrophobins are
secreted into the growth medium and allow the hyphae to grow up
into the air under reduced surface tension.
26
from 72 to 32 mJ/m
2
29
b
a
Figure 3.3
Hydrophobins can reverse the wettability of surfaces.
Photograph showing water droplets sitting on (a) a Teflon TM -
coated slide and (b) EAS-coated Teflon TM slide. The water
contact angle is marked and can be seen to be significantly
reduced in (b) when compared to (a).
Despite the many similarities that exist between Class I and
Class II hydrophobins, the bioinformatics-based division of
hydrophobins mirrors key physiochemical differences between
the two classes. Notably, class II hydrophobins form assemblies
without a regular morphology and can be solubilized in alcohol
solutions and in hot SDS. So far, all of the hydrophobins that form
the robust, regular rodlets identified on outer fungal surfaces are
strictly members from the Class I family. These rodlets are fibrillar in
morphology, insoluble in SDS, and can only be solubilized by strong
acid treatment, all of which are characteristics which call to mind
amyloid-like structures.
3.4
Hydrophobins and Amyloid
The similarities between the morphological and structural characteri-
stics of Class I hydrophobin rodlets and amyloid fibrils were first
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