Hydrophobin
| Fungal hydrophobin | |||||||||
|---|---|---|---|---|---|---|---|---|---|
Structure of hydrophobin HFBII from Trichoderma reesei | |||||||||
| Identifiers | |||||||||
| Symbol | Hydrophobin_2 | ||||||||
| Pfam | PF06766 | ||||||||
| InterPro | IPR010636 | ||||||||
| PROSITE | PDOC00739 | ||||||||
| SCOP2 | 1r2m / SCOPe / SUPFAM | ||||||||
| OPM superfamily | 96 | ||||||||
| OPM protein | 1r2m | ||||||||
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| Hydrophobin | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | Hydrophobin | ||||||||
| Pfam | PF01185 | ||||||||
| InterPro | IPR001338 | ||||||||
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Hydrophobins are a group of small (~100 amino acids) cysteine-rich proteins that were discovered in filamentous fungi that are lichenized or not. Later similar proteins were also found in Bacteria. Hydrophobins are known for their ability to form a hydrophobic (water-repellent) coating on the surface of an object. They were first discovered and separated in Schizophyllum commune in 1991. Based on differences in hydropathy patterns and biophysical properties, they can be divided into two categories: class I and class II. Hydrophobins can self-assemble into a monolayer on hydrophilic:hydrophobic interfaces such as a water:air interface. Class I monolayer contains the same core structure as amyloid fibrils, and is positive to Congo red and thioflavin T. The monolayer formed by class I hydrophobins has a highly ordered structure, and can only be dissociated by concentrated trifluoroacetate or formic acid. Monolayer assembly involves large structural rearrangements with respect to the monomer.
Fungi make complex aerial structures and spores even in aqueous environments.
Hydrophobins have been identified in lichens as well as non-lichenized ascomycetes and basidiomycetes; whether they exist in other groups is not known. Hydrophobins are generally found on the outer surface of conidia and of the hyphal wall, and may be involved in mediating contact and communication between the fungus and its environment. Some family members contain multiple copies of the domain.
Hydrophobins have been found to be structurally and functionally similar to cerato-platanins, another group of small cysteine-rich proteins, which also contain a high percentage of hydrophobic amino acids, and are also associated with hyphal growth.
This family of proteins includes the rodlet proteins of Neurospora crassa (gene eas) and Emericella nidulans (gene rodA), these proteins are the main component of the hydrophobic sheath covering the surface of many fungal spores.
Genomic sequencing of two fungi from dry or salty environments (Wallemia sebi and W. ichthyophaga) revealed that these species contain predicted hydrophobins with unusually high proportion of acidic amino acids and therefore with potentially novel characteristics. High proportion of acidic amino acids is thought to be an adaptation of proteins to high concentrations of salt.