Class I and class II hydrophobins are small secreted fungal proteins that p
lay a role in a broad range of processes in the growth and development of f
ilamentous fungi. For instance, they are involved in the formation of aeria
l structures and in the attachment of hyphae to hydrophobic surfaces. The m
echanisms by which hydrophobins fulfill these functions are based on their
property to self-assemble at hydrophilic-hydrophobic interfaces into a 10 n
m-thin highly amphipathic film. Complementation studies have shown that cla
ss I hydrophobins belong to a closely related group of morphogenetic protei
ns, but that they have evolved to function at specific interfaces. Recent e
vidence indicates that hydrophobins do not only function by self-assembly.
Monomeric hydrophobin has been implicated in cell-wall assembly, but the un
derlying mechanism is not yet clear. In addition, hydrophobin monomers coul
d act as toxins and elicitors.