Amphipathic Proteins
Hydrophobins are small amphipathic
proteins secreted by filamentous fungi which are very important in the
development and growth of the organisms. The outside of fungal aerial
structures (e.g. mushrooms and spores) are covered with
hydrophobins, which are organized in a typical mosaic of
rodlets. The exposed side of such a coating is
noticeably hydrophobic.
Hydrophobins demonstrate a strong
self-assembling character when put in contact with a
hydrophobic-hydrophilic interface, forming a highly insoluble amphipathic
membrane of only 10 nm thick. The interface can range from the interface
between air and liquid interface to the interface between water and
hydrophobic solid/liquid. As the membrane is amphipathic, it can change
the nature of the surface; a hydrophobic surface can be made hydrophilic
and a hydrophilic surface can be made hydrophobic.
This class of amphipathic proteins
is not restricted to the fungal kingdom, but can also be found in
prokaryotes. BiOMaDe is examining a variety of hydrophobins from different
sources to find proteins with new or improved properties, a process which
is being aided by the increasing availability of genome sequences for
various organisms. At the same time BiOMaDe’s scientists are actively
researching the structure/function relationships of these proteins in
detail to understand how the sequence and chemical composition influences
the structure and properties of the protein. The resulting data is the
basis for chemical and mutagenic approaches for modifying both structures
and properties.
The low immunogenicity, the ability
to form stable films and the ability to modify surfaces via self-assembly
make hydrophobins extremely interesting proteins for technical and medical
applications. They can be used, for instance, to
make surfaces bio-compatible or as delivery vehicles for drugs. In the
case of drug delivery one is often dealing with compounds which are
hydrophobic and are suspended in hydrophobic media. Hydrophobins, when
added to a watery solution containing hydrophobic components such as oil
droplets, organize themselves around the droplet and self- associate into
a stable membrane, which is the basis for this delivery vehicle.
