Summary: Fungal hydrophobin
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Hydrophobin Edit Wikipedia article
Structure of hydrophobin HFBI from Trichoderma reesei
Hydrophobins are a group of small (~100 amino acids) cysteine-rich proteins that are expressed only by filamentous fungi. They 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 hydrophobic:hydrophilic 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.
Hydrophobins have been identified in 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.
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.
Hydrophobins are characterised by the presence of 8 conserved cysteine residues that form 4 disulphide bonds. They are able to reverse the wettability of surfaces by spontaneous self-assembly of the monomeric proteins into amphipathic monolayers at hydrophobic:hydrophilic surfaces. Despite this common feature, hydrophobins are subdivided into two classes based on differences on their monomeric structure, such as the spacing between the cysteine residues, and based on the different physicochemical properties of the amphipatic monolayers they form  Extensive structural analyses of individual hydrophobins from the two classes have elucidated that the morphological and physical differences between the class I and class II polymer forms are the results of significant structural differences at the monomer-assembly level.
Class I hydrophobins are characterised by having a quite diverse amino acid sequence between different types (with exception of the conserved cysteine residues), and compared to class II, they have long, varied inter-cysteine spacing. They form rodlets which have been identified as functional amyloids due to their amyloid-like characteristics as seen in X-ray diffraction studies and confirmed by their capacity to bind to amyloid-specific dyes such as Congo red and Thioflavin T. The formation of rodlets involves conformational changes  that lead to formation of an extremely robust β-sheet structure  that can only be depolymerised by treatment with strong acids. The rodlets can spontaneously form ordered monolayers by lateral assembly, displaying a regular fibrillary morphology on hydrophobic:hydrophilic interfaces. The most well characterised class I hydrophobin is EAS, which coats the spores of the fungus Neurospora crassa, followed by characterisation of DewA from Aspergillus nidulans.
Class II hydrophobins have overall a more conserved amino acid sequence between the different types and, contrary to class, I they have short, regular inter-cysteine spacing. Opposite to class I, the class II hydrophobins monolayer formed at hydrophobic:hydrophilic interfaces is not fibrillar and it is not associated with formation of amyloid-structures, nor with large conformational changes. Nonetheless, high resolution atomic-force microscopy studies revealed the formation of a notable hexagonal repeating pattern over surfaces coated with the class II hydrophobin HBFI, meaning that these proteins are also able to form an ordered network in surface films.
The crystal structures or HFBI and HFBII from Trichoderma reesei were the first class II hydrophobins to be determined.
Rodlet self-assembly of class I hydrophobins
There is special interest in understanding the mechanism underlying class I monomers self-assembly that leads to formation of tough, ordered amphipathic rodlet monolayers, due to their intrinsic properties and due to substantial information available from several characterisation studies of the class I hydrophobins EAS and DewA. These mechanisms have been greatly studied by targeted mutagenesis in an effort to identify the key amino acid sequence regions driving rodlet self-assembly. A model for the monomeric form of EAS was proposed by Kwan et al. (2006) from structural data obtained from NMR spectroscopy and X-ray diffraction experiments that indicated the presence of four-stranded, antiparallel β-barrel core structure in EAS that allows monomer linking through backbone H-bonding. There are secondary elements around this β-barrel core like the Cys3-Cys4 and Cys7-Cys8 loops. This model is consistent with the amyloid-like structure that class I rodlets form, in which the β-strands are oriented perpendicular to the cross-β scaffold axis of the fibre.
Site-directed mutagenesis of EAS has given insights into the specific structural changes responsible for self-assembly of monomers into rodlets and subsequent formation of amphipathic monolayer in hydrophobic:hydrophilic interfaces. Kwan et al. (2008) reported that the long hydrophobic Cys3-Cys4 loop is not required for rodlet assembly because its deletion does not affect the folding and physical properties of the monomeric protein, neither the morphology of the polymeric rodlet form. Instead, a region of the short Cys7-Cys8 loop, containing mainly uncharged polar residues, has been found to be critical for rodlet assembly.
Characterization of EAS secondary elements involved in rodlet assembly have given insights into the mechanism behind class I hydrophobins self-assembly, but important structural differences with DewA, another class I hydrophobin, suggest that the mechanisms driving rodlet assembly vary among different types of hydrophobins. Like EAS, DewA also has a β-barrel core structure, but it differs significantly from it because of its considerable content of helical secondary elements. A unique feature of DewA is its capacity to exist as two types of conformers in solution, both able to form rodlet assemblies but at different rates. Despite these differences in structural and self-assembly mechanisms, both EAS and DewA form robust fibrillar monolayers, meaning that there must exist several pathways, protein sequences and tertiary conformations able to self-assemble into amphipathic monolayers. Further characterisation of both EAS and DewA and their rodlet self-assembly mechanisms will open up opportunities for rational design of hydrophobins with novel biotechnological applications.
Potentiality for use
Since the very first studies that gave insights into the properties of hydrophobins, these small proteins have been regarded as great candidates for technological use. The detailed understanding of the molecular mechanisms underlying hydrophobin self-assembly into amphipathic monolayer in hydrophobic:hydrophilic interfaces is of great academic interest but mainly of commercial interest. This is because a deep understanding of the elements driving these mechanisms would allow engineering of hydrophobins (or other biomolecules) for nano and biotechnological applications. An example is that the hydrophobin-coating of carbon nanotubes was found to increase their solubility and reduce their toxicity, a finding that increases the prospects of carbon nanotubes to be used as vehicles for drug delivery. Other areas of potential use of hydrophobins include:
- Fabrication and coating of nanodevices and medical implants to increase biocompatibility.
- Emulsifiers in food industry and personal care products.
- Class I high stability can be very useful in the coating of surfaces of prolonged use or under harsh conditions.
- The easy dissociation of a class II hydrophobin monolayer might be desirable and this can easily be achieved by the use of detergents and alcohols.
- The use of hydrophobins in protein purification, drug delivery  and cell attachment has been reported.
- Sunde M, Kwan AH, Templeton MD, Beever RE, Mackay JP (October 2008). "Structural analysis of hydrophobins". Micron. 39 (7): 773–84. doi:10.1016/j.micron.2007.08.003. PMID 17875392.
- Wessels J, De Vries O, Asgeirsdottir SA, Schuren F (1991). "Hydrophobin Genes Involved in Formation of Aerial Hyphae and Fruit Bodies in Schizophyllum.". Plant Cell. 3 (8): 793–799. doi:10.1105/tpc.3.8.793. PMC . PMID 12324614.
- Morris V. K.; Linser R.; Wilde K. L.; Duff A. P.; Sunde M.; Kwan A. H. (2012). "Solid-State NMR Spectroscopy of Functional Amyloid from a Fungal Hydrophobin: A Well-Ordered β-Sheet Core Amidst Structural Heterogeneity". Angew. Chem. Int. Ed. 51: 12621–12625. doi:10.1002/anie.201205625.
- Wösten (2001). "Hydrophobins: multipurpose proteins". Annual Review of Microbiology. 55: 625–646. doi:10.1146/annurev.micro.55.1.625. PMID 11544369.
- Whiteford JR, Spanu PD (2001). "The hydrophobin HCf-1 of Cladosporium fulvum is required for efficient water-mediated dispersal of conidia". Fungal Genet. Biol. 32 (3): 159–168. doi:10.1006/fgbi.2001.1263. PMID 11343402.
- Stringer MA, Dean RA, Sewall TC, Timberlake WE (July 1991). "Rodletless, a new Aspergillus developmental mutant induced by directed gene inactivation". Genes Dev. 5 (7): 1161–71. doi:10.1101/gad.5.7.1161. PMID 2065971.
- Lauter FR, Russo VE, Yanofsky C (December 1992). "Developmental and light regulation of eas, the structural gene for the rodlet protein of Neurospora". Genes Dev. 6 (12A): 2373–81. doi:10.1101/gad.6.12a.2373. PMID 1459459.
- Zajc, J.; Liu, Y.; Dai, W.; Yang, Z.; Hu, J.; Gostin Ar, C.; Gunde-Cimerman, N. (2013). "Genome and transcriptome sequencing of the halophilic fungus Wallemia ichthyophaga: Haloadaptations present and absent". BMC Genomics. 14: 617. doi:10.1186/1471-2164-14-617. PMC . PMID 24034603.
- Madern, D.; Ebel, C.; Zaccai, G. (2000). "Halophilic adaptation of enzymes". Extremophiles : life under extreme conditions. 4 (2): 91–98. doi:10.1007/s007920050142. PMID 10805563.
- Macindoe, I. et al., 2012. Self-assembly of functional, amphipathic amyloid monolayers by the fungal hydrophobin EAS. Proceedings of the National Academy of Sciences, 109(14), pp. E804-E811
- Wessels, J., 1994. Developmental Regulation of Fungal Cell Wall Formation. Annual Review Phytopathology, 32(1), pp. 413-437
- Wessels, J., 1996. Hydrophobins: proteins that change the nature of the fungal surface. Advances in microbial physiology, Volume 38, pp. 1-45
- Kwan, A. et al., 2006. Structural basis for rodlet assembly in fungal hydrophobins. Proceedings of the National Academy of Sciences, 103(10), pp. 3621-3626
- Eichner, T. & Radford, S. E., 2011. A diversity of assembly mechanisms of a generic amyloid fold. Molecular Cell, Volume 43, pp. 8-18
- Wösten, H. & Wessels, J., 1979. Purification and chemical characterization of the rodlet layer of Neurospora crassa conidia. Journal of Bacteriology, Volume 140, pp. 1063-1070
- de Vries, O. M., Fekkes, M. P., Wösten, H. A. & Wessels, J. G., 1993. Insoluble hydrophobin complexes in the walls of Schizophyllum commune and other filamentous fungi. Archives of Microbiology, 159(4), pp. 330-335
- Ren, Q., Kwan, A. & Sunde, M., 2013. Two forms and two faces, multiple states and multiple uses: Properties and applications of the self-assembling fungal hydrophobins. Biopolymers, 100(6), pp. 601-612
- Morris, V., Kwan, A. & Sunde, M., 2012. Analysis of the Structure and Conformational States of DewA Gives Insight into the Assembly of the Fungal Hydrophobins. Journal of Molecular Biology, Volume 452, pp. 245-256
- Szilvay, G. et al., 2007. Self-Assembled Hydrophobin Protein Films at the Air−Water Interface: Structural Analysis and Molecular Engineering. Biochemistry, 46(9), pp. 2345-2354
- Sunde, M. et al., 1997. Common core structure of amyloid fibrils by synchrotron X-ray diffraction. Journal of Molecular Biology, 273(3), pp. 729-739
- Kwan, A. et al., 2008. The Cys3–Cys4 loop of the hydrophobin EAS is not required for rodlet formation and surface activity. Journal of Molecular Biology, 382(3), pp. 708-720
- Morris, V., Kwan, A., Mackay, J. & Sunde, M., 2011. Backbone and sidechain 1H, 13C and 15N chemical shift assignments of the hydrophobin DewA from Aspergillus nidulans. Biomolecular NMR assignments, 6(1), pp. 83-86
- Wessels, J., 1994. Developmental Regulation of Fungal Cell Wall Formation.. Annual Review Phytopathology, 32(1), pp. 413-437
- Yang, W. et al., 2012. Surface functionalization of carbon nanomaterials by self-assembling hydrophobin proteins. Biopolymers, 99(1), pp. 84-94
- Lnder, M. et al., 2004. Efficient Purification of Recombinant Proteins Using Hydrophobins as Tags in Surfactant-Based Two-Phase Systems. Biochemistry, 43(37), pp. 11873-11882
- Collén, A. et al., 2002. Extraction of endoglucanase I (Cel7B) fusion proteins from Trichoderma reesei culture filtrate in a poly(ethylene glycol)–phosphate aqueous two-phase system. Journal of Chromatography A, 943(1), pp. 55-62
- Joensuu, J. et al., 2009. Hydrophobin Fusions for High-Level Transient Protein Expression and Purification in Nicotiana benthamiana. Plant Physiology, 152(2), pp. 622-633
- Akanbi, M. et al., 2010. Use of hydrophobins in formulation of water insoluble drugs for oral administration. Colloids and Surfaces B: Biointerfaces, 75(2), pp. 526-531
- Bimbo, L. et al., 2012. Cellular interactions of surface modified nanoporous silicon particles. Nanoscale, 4(10), pp. 3184-3192
- Sarparanta, M. et al., 2012. Intravenous Delivery of Hydrophobin-Functionalized Porous Silicon Nanoparticles: Stability, Plasma Protein Adsorption and Biodistribution. Mol. Pharmaceutics, 9(3), pp. 654-663
- Nakari-Setala, T. et al., 2002. Expression of a Fungal Hydrophobin in the Saccharomyces cerevisiae Cell Wall: Effect on Cell Surface Properties and Immobilization. Applied and Environmental Microbiology, 68(7), pp. 3385-3391
- Niu, B. et al., 2012. Expression and characterization of hydrophobin HGFI fused with the cell-specific peptide TPS in Pichia pastoris. Protein Expression and Purification, 83(1), pp. 92-97
- Boeuf, S. et al., 2012. Engineering hydrophobin DewA to generate surfaces that enhance adhesion of human but not bacterial cells. Acta Biomaterialia, 8(3), pp. 1037-1047
- Hektor, H. & Scholtmeijer, K., 2005. Hydrophobins: proteins with potential. Current Opinion in Biotechnology, 16(4), pp. 434-439
- Cox, P. & Hooley, P., 2009. Hydrophobins: New prospects for biotechnology. Fungal Biology Reviews, 23(1), pp. 40-47
- Scholtmeijer K (2000). Expression and engineering of hydrophobin genes (Ph.D. thesis). University of Groningen.
- Hakanpää J, Paananen A, Askolin S, Nakari-Setälä T, Parkkinen T, Penttilä M, Linder MB, Rouvinen J (January 2004). "Atomic resolution structure of the HFBII hydrophobin, a self-assembling amphiphile". J. Biol. Chem. 279 (1): 534–9. doi:10.1074/jbc.M309650200. PMID 14555650.
- Wösten HA, de Vocht ML (September 2000). "Hydrophobins, the fungal coat unravelled". Biochim. Biophys. Acta. 1469 (2): 79–86. doi:10.1016/S0304-4157(00)00002-2. PMID 10998570.
- Aimanianda V, Bayry J, Bozza S, Kniemeyer O, Perruccio K, Elluru SR, Clavaud C, Paris S, Brakhage AA, Kaveri SV, Romani L, Latgé JP (August 2009). "Surface hydrophobin prevents immune recognition of airborne fungal spores". Nature. 460 (7259): 1117–21. doi:10.1038/nature08264. PMID 19713928.
This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.
Fungal hydrophobin Provide feedback
This is a family of fungal hydrophobins that seems to be restricted to ascomycetes. These are small, moderately hydrophobic extracellular proteins that have eight cysteine residues arranged in a strictly conserved motif. 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 . Note that some family members contain multiple copies.
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR010636
This is a family of fungal hydrophobins that seems to be restricted to ascomycetes. Hydrophobins are small, moderately hydrophobic extracellular proteins that have eight cysteine residues arranged in a strictly conserved motif. 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 [PUBMED:11343402]. The family includes cryparin, which is a cell-surface-associated hydrophobin secreted by filamentous fungi [PUBMED:10584000], and cerato-ulmin, a secreted toxin hydrophobin involved in Dutch Elm disease [PUBMED:9344630].
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Cellular component||extracellular region (GO:0005576)|
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|Seed source:||Pfam-B_3587 (release 10.0)|
|Author:||Vella Briffa B|
|Number in seed:||87|
|Number in full:||342|
|Average length of the domain:||63.80 aa|
|Average identity of full alignment:||42 %|
|Average coverage of the sequence by the domain:||43.21 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 26740544 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||10|
|Download:||download the raw HMM for this family|
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The tree is built by looking at each sequence in the full alignment for the family. We take the name of the species given by UniProt and try to map that to the full taxonomic tree from NCBI. In some cases, the name chosen by UniProt does not map to any node in the NCBI tree, perhaps because the chosen name is listed as a synonym or a misspelling in the NCBI taxonomy.
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The tree shows the occurrence of this domain across different species. More...
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For all of the domain matches in a full alignment, we count the number that are found on all sequences in the alignment. This total is shown in the purple box.
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Finally, we group sequences from the same organism according to the NCBI code that is assigned by UniProt, allowing us to count the number of distinct sequences on which the domain is found. This value is shown in the pink boxes.
We use the NCBI species tree to group organisms according to their taxonomy and this forms the structure of the displayed tree. Note that in some cases the trees are too large (have too many nodes) to allow us to build an interactive tree, but in most cases you can still view the tree in a plain text, non-interactive representation. Those species which are represented in the seed alignment for this domain are highlighted.
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There is 1 interaction for this family. More...
We determine these interactions using iPfam, which considers the interactions between residues in three-dimensional protein structures and maps those interactions back to Pfam families. You can find more information about the iPfam algorithm in the journal article that accompanies the website.
For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the Hydrophobin_2 domain has been found. There are 26 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.
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