Biology Reference
In-Depth Information
3.3
The Two Classes of Hydrophobins
Comparative analysis of hydrophobin sequences showed that in spite
of the low levels of sequence homology between these proteins, they
share a very distinctive arrangement of eight cysteine residues in
a unique pattern (X
-C-X
-CC-X
-C-X
-C-X
-CC-X
-C-
2-38
5-10
11-44
8-23
5-9
6-21
24
X
), including two pairs of adjacent cysteine residues (Fig. 3.2).
2-13
Within the hydrophobin family, proteins can be further separated
into Class I and Class II hydrophobins, on the basis of the distinct
hydropathy profiles displayed by these classes and the conservation
in the spacing of amino acids between the cysteine residues. This
distinction between the sequence characteristics of Class I and Class
II hydrophobins has been maintained and clarified as increasing
numbers of hydrophobins have been sequenced.
25
Figure 3.2
Alignment of Class I and Class II hydrophobins. Alignment of
representative set of Class I and Class II hydrophobin sequences.
This illustrates the conserved pattern of eight cysteine
residues, including the two pairs of adjacent cysteines, and the
differences in distribution of these cysteine residues between
the two classes. It is also clear that the Class I sequences
display very limited sequence homology and great variation in
the length of the inter-cysteine regions. In contrast, the Class II
hydrophobins display much higher conservation of sequence
and loop length. Extent of sequence conservation is indicated
by shading from black (absolutely conserved), through shades
of grey, to white (not conserved).
The monolayers formed by members of both classes of
hydrophobin are amphipathic. When the layers are assembled
in
vitro
, their orientation depends on the nature of the surface, that
is, hydrophobin monolayers are able to reverse the wettability of
surfaces.
26,27
When assembled on a glass slide, SC3 raises the water
contact angle from approximately 40
°
for naked glass to 55
°
, whereas
an SC3 coating on Teflon
TM
reduces the water contact angle
28
from
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