Hydrophobins: Exceptional proteins for many applications in brewery environment and other bio-industries

Improved extraction and purification of the hydrophobin HFBI

Hydrophobins (HFBs) are a group of highly functional, low molecular weight proteins with the ability to self-assemble at hydrophobic-hydrophilic interfaces. The surface active, cysteine-rich proteins are found in filamentous fungi such as Trichoderma reesei. In the present study multiple extraction solvents and conditions were screened for the mycelium bound hydrophobin HFBI and the effects on the total amount of extracted proteins, HFBI recovery and HFBI gushing activity were investigated to gain a more thorough scientific insight on the extraction efficiency and selectivity. Results indicated the enhanced selectivity for HFBI extraction from the fungal biomass using 60% ethanol compared to solutions containing 1% sodium dodecyl sulphate (SDS). Complementing the higher selectivity, HFBI recovery was increased from 6.9 ± 0.6 mg HFBI (1% SDS) to 9.4 ± 0.4 mg HFBI per gram dry fungal biomass for extracts containing 60% ethanol. Furthermore, subsequent to HPLC purification, Cold Induced Phase Separation (CIPS) of acetonitrile-water systems was investigated at different pH levels. CIPS at pH 2.0 was found to effectively remove the majority of sorbicillinoid pigments from the purified HFBI fraction. The improved method resulted in a recovery of 85.4% of the extracted HFBI after final purification.

Soluble Expression and Efficient Purification of Recombinant Class I Hydrophobin DewA

Hydrophobins are small proteins (<20 kDa) with an amphipathic tertiary structure that are secreted by various filamentous fungi. Their amphipathic properties provide surfactant-like activity, leading to the formation of robust amphipathic layers at hydrophilic–hydrophobic interfaces, which make them useful for a wide variety of industrial fields spanning protein immobilization to surface functionalization. However, the industrial use of recombinant hydrophobins has been hampered due to low yield from inclusion bodies owing to the complicated process, including an auxiliary refolding step. Herein, we report the soluble expression of a recombinant class I hydrophobin DewA originating from Aspergillus nidulans, and its efficient purification from recombinant Escherichia coli. Soluble expression of the recombinant hydrophobin DewA was achieved by a tagging strategy using a systematically designed expression tag (ramp tag) that was fused to the N-terminus of DewA lacking the innate signal sequence. Highly expressed recombinant hydrophobin DewA in a soluble form was efficiently purified by a modified aqueous two-phase separation technique using isopropyl alcohol. Our approach for expression and purification of the recombinant hydrophobin DewA in E. coli shed light on the industrial production of hydrophobins from prokaryotic hosts.

Expression of BMP2-Hydrophobin fusion protein in the tobacco plant and molecular dynamic evaluation of its simulated model

Plants are one of the ideal models for therapeutic protein production, however the recombinant protein purification problems in them must be overcome. Bone Morphogenetic Protein2 (BMP2) is employed for the restoration and construction of bone tissues. Hydrophobin is a fungal based protein with high hydrophobic characteristics. Due to this specificity, it is suitable for the purification of chimer protein from complex solutions when is fused to a protein utilizing an aqueous two-phase (A2P) technique. The plant optimized mature human BMP2 gene was designed and evaluated by in silico method. This process involves simulating molecular dynamics using the RMSD, RMSF and Gyration radius indexes. The synthesized Hyd-BMP2 gene was cloned into a pTRAkc-ERH plasmid and Transferred into Agrobacterium (Gv3101). The Nicotiana benthamiana plant leaves were co-agroinfiltrated with HA-Hyd-BMP2 and P19-pCambia1304 containing silencing suppressor. After purification of plant extract utilizing the A2P method, the sample was subjected to SDS-PAGE and Western-blot. By in silico study, the simulated fusion protein profitably shows reasonable protein compactness and the effect of amino acid substitution on protein-protein interaction is not remarkable. Western-blotting using anti HA tag has shown that the A2P technique partially purified the two 22 kDa and 44 kDa forms of Hydrophobin-BMP2. These results confirmed the presence of monomer and dimer forms of Hydrophobin-BMP2 proteins. Moreover, the expression level of the protein using P19 silencing suppressor increased six times and to 0.018% as shown by ELISA. This study presents a fast and easy technique for the purification of transient expressed pharmaceutical proteins from plants.

Interfacial Activity of Phasin PhaF from Pseudomonas putida KT2440 at Hydrophobic-Hydrophilic Biointerfaces

Phasins, the major proteins coating polyhydroxyalkanoate (PHA) granules, have been proposed as suitable biosurfactants for multiple applications because of their amphiphilic nature. In this work, we analyzed the interfacial activity of the amphiphilic α-helical phasin PhaF from Pseudomonas putida KT2440 at different hydrophobic-hydrophilic interfacial environments. The binding of PhaF to surfaces containing PHA or phospholipids, postulated as structural components of PHA granules, was confirmed in vitro using supported lipid bilayers and confocal microscopy, with polyhydroxyoctanoate- co-hexanoate P(HO- co-HHx) and Escherichia coli lipid extract as model systems. The surfactant-like capabilities of PhaF were determined by measuring changes in surface pressure in Langmuir devices. PhaF spontaneously adsorbed at the air-water interface, reducing the surface tension from 72 mN/m (water surface tension at 25 °C) to 50 mN/m. The differences in the adsorption of the protein in the presence of different phospholipid films showed a marked preference for phosphatidylglycerol species, such as 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphoglycerol. The PHA-binding domain of PhaF (BioF) conserved a similar surface activity to PhaF, suggesting that it is responsible for the surfactant properties of the whole protein. These new findings not only increase our knowledge about the role of phasins in the PHA machinery but also open new outlooks for the application of these proteins as biosurfactants.

Adhesion Properties of Freestanding Hydrophobin Bilayers

Hydrophobins are a family of small-sized proteins featuring a distinct hydrophobic patch on the protein's surface, rendering them amphiphilic. This particularity allows hydrophobins to self-assemble into monolayers at any hydrophilic/hydrophobic interface. Moreover, stable pure protein bilayers can be created from two interfacial hydrophobin monolayers by contacting either their hydrophobic or their hydrophilic sides. In this study, this is achieved via a microfluidic approach, in which also the bilayers' adhesion energy can be determined. This enables us to study the origin of the adhesion of hydrophobic and hydrophilic core bilayers made from the class II hydrophobins HFBI and HFBII. Using different fluid media in this setup and introducing genetically modified variants of the HFBI molecule, the different force contributions to the adhesion of the bilayer sheets are studied. It was found that in the hydrophilic contact situation, the adhesive interaction was higher than that in the hydrophobic contact situation and could be even enhanced by reducing the contributions of electrostatic interactions. This effect indicates that the van der Waals interaction is the dominant contribution that explains the stability of the observed bilayers.

Hydrophobin coating prevents Staphylococcus epidermidis biofilm formation on different surfaces

Staphylococcus epidermidis is a significant nosocomial pathogen in predisposed hosts because of its capability of forming a biofilm on indwelling medical devices. The initial stage of biofilm formation has a key role in S. epidermidis abiotic surface colonization. Recently, many strategies have been developed to create new anti-biofilm surfaces able to control bacterial adhesion mechanisms. In this work, the self-assembled amphiphilic layers formed by two fungal hydrophobins (Vmh2 and Pac3) have proven to be able to reduce the biofilm formed by different strains of S. epidermidis on polystyrene surfaces. The reduction in the biofilm thickness on the coated surfaces and the preservation of cell vitality have been demonstrated through confocal laser scanning microscope analysis. Moreover, the anti-biofilm efficiency of the self-assembled layers on different medically relevant materials has also been demonstrated using a CDC biofilm reactor.

Characterization of a Basidiomycota hydrophobin reveals the structural basis for a high-similarity Class I subdivision

Class I hydrophobins are functional amyloids secreted by fungi. They self-assemble into organized films at interfaces producing structures that include cellular adhesion points and hydrophobic coatings. Here, we present the first structure and solution properties of a unique Class I protein sequence of Basidiomycota origin: the Schizophyllum commune hydrophobin SC16 (hyd1). While the core β-barrel structure and disulphide bridging characteristic of the hydrophobin family are conserved, its surface properties and secondary structure elements are reminiscent of both Class I and II hydrophobins. Sequence analyses of hydrophobins from 215 fungal species suggest this structure is largely applicable to a high-identity Basidiomycota Class I subdivision (IB). To validate this prediction, structural analysis of a comparatively distinct Class IB sequence from a different fungal order, namely the Phanerochaete carnosa PcaHyd1, indicates secondary structure properties similar to that of SC16. Together, these results form an experimental basis for a high-identity Class I subdivision and contribute to our understanding of functional amyloid formation.

HFB7 - A novel orphan hydrophobin of the Harzianum and Virens clades of Trichoderma, is involved in response to biotic and abiotic stresses

Hydrophobins are small secreted cysteine-rich proteins exclusively found in fungi. They are able to self-assemble in single molecular layers at hydrophobic-hydrophilic interfaces and can therefore be directly involved in establishment of fungi in their habitat. The genomes of filamentous mycotrophic fungi Trichoderma encode a rich diversity of hydrophobins, which are divided in several groups based on their structure and evolution. Here we describe a new member of class II hydrophobins, HFB7, that has a taxonomically restricted occurrence in Harzianum and Virens clades of Trichoderma. Evolutionary analysis reveals that HFB7 proteins form a separate clade distinct from other Trichoderma class II hydrophobins and that genes encoding them evolve under positive selection pressure. Homology modelling of HFB7 structure in comparison to T. reesei HFB2 reveals that the two large hydrophobic patches on the surface of the protein are remarkably conserved between the two hydrophobins despite significant difference in their primary structures. Expression of hfb7 gene in T. virens increases at interactions with other fungi and a plant and in response to a diversity of abiotic stress conditions, and is also upregulated during formation of aerial mycelium in a standing liquid culture. This upregulation significantly exceeds that of expression of hfb7 under a strong constitutive promoter, and T. virens strains overexpressing hfb7 thus display only changes in traits characterized by low hfb7 expression, i.e. faster growth in submerged liquid culture. The hfb7 gene is not expressed in conidia. Our data allow to conclude that this protein is involved in defence of Trichoderma against a diversity of stress factors related to the oxidative stress. Moreover, HFB7 likely helps in the establishment of the fungus in wetlands or other conditions related to high humidity.

Recent Advances in Fungal Hydrophobin Towards Using in Industry

Fungal hydrophobin is a family of low molecular weight proteins consisting of four disulfide bridges and an extraordinary hydrophobic patch. The hydrophobic patch of hydrophobins and the molecules of gaseous CO2 may interact together and form the stable CO2-nanobubbles covered by an elastic membrane in carbonated beverages. The nanobubbles provide the required energy to provoke primary gushing. Due to the hydrophobicity of hydrophobin, this protein is used as a biosurfactant, foaming agent or encapsulating agent in food products and medicine formulations. Increasing demands for using of hydrophobins led to a challenge regarding production and purification of this product. However, the main issue to use hydrophobin in the industry is the regulatory affairs: yet there is no approved legislation for using hydrophobin in food and beverages. To comply with the legislation, establishing a consistent method for obtaining pure hydrophobins is necessary. Currently, few research teams in Europe are focusing on different aspects of hydrophobins. In this paper, an up-to-date collection of highlights from those special groups about the bio-chemical and physicochemical characteristics of hydrophobins have been studied. The recent advances of those groups concerning the production and purification, positive applications and negative function of hydrophobin are also summarised.

Selective isolation of hydrophobin SC3 by solid-phase extraction with polytetrafluoroethylene microparticles and subsequent mass spectrometric analysis

Hydrophobins are small proteins that play a role in a number of processes during the filamentous fungi growth and development. These proteins are characterized by the self-assembly of their molecules into an amphipathic membrane at hydrophilic-hydrophobic interfaces. Isolation and purification of hydrophobins generally present a challenge in their analysis. Hydrophobin SC3 from Schizophyllum commune was selected as a representative of class I hydrophobins in this work. A novel procedure for selective and effective isolation of hydrophobin SC3 based on solid-phase extraction with polytetrafluoroethylene microparticles loaded in a small self-made microcolumn is reported. The tailored binding of hydrophobins to polytetrafluoroethylene followed by harsh elution conditions resulted in a highly specific isolation of hydrophobin SC3 from the model mixture of ten proteins. The presented isolation protocol can have a positive impact on the analysis and utilization of these proteins including all class I hydrophobins. Hydrophobin SC3 was further subjected to reduction of its highly stable disulfide bonds and to chymotryptic digestion followed by mass spectrometric analysis. The isolation and digestion protocols presented in this work make the analysis of these highly hydrophobic and compact proteins possible.

Adsorption of hydrophobin on different self-assembled monolayers: the role of the hydrophobic dipole and the electric dipole

In this work, the adsorptions of hydrophobin (HFBI) on four different self-assembled monolayers (SAMs) (i.e., CH3-SAM, OH-SAM, COOH-SAM, and NH2-SAM) were investigated by parallel tempering Monte Carlo and molecular dynamics simulations. Simulation results indicate that the orientation of HFBI adsorbed on neutral surfaces is dominated by a hydrophobic dipole. HFBI adsorbs on the hydrophobic CH3-SAM through its hydrophobic patch and adopts a nearly vertical hydrophobic dipole relative to the surface, while it is nearly horizontal when adsorbed on the hydrophilic OH-SAM. For charged SAM surfaces, HFBI adopts a nearly vertical electric dipole relative to the surface. HFBI has the narrowest orientation distribution on the CH3-SAM, and thus can form an ordered monolayer and reverse the wettability of the surface. For HFBI adsorption on charged SAMs, the adsorption strength weakens as the surface charge density increases. Compared with those on other SAMs, a larger area of the hydrophobic patch is exposed to the solution when HFBI adsorbs on the NH2-SAM. This leads to an increase of the hydrophobicity of the surface, which is consistent with the experimental results. The binding of HFBI to the CH3-SAM is mainly through hydrophobic interactions, while it is mediated through a hydration water layer near the surface for the OH-SAM. For the charged SAM surfaces, the adsorption is mainly induced by electrostatic interactions between the charged surfaces and the oppositely charged residues. The effect of a hydrophobic dipole on protein adsorption onto hydrophobic surfaces is similar to that of an electric dipole for charged surfaces. Therefore, the hydrophobic dipole may be applied to predict the probable orientations of protein adsorbed on hydrophobic surfaces.

Fungal Hydrophobin Proteins Produce Self-Assembling Protein Films with Diverse Structure and Chemical Stability

Hydrophobins are small proteins secreted by fungi and which spontaneously assemble into amphipathic layers at hydrophilic-hydrophobic interfaces. We have examined the self-assembly of the Class I hydrophobins EAS_∆15 and DewA, the Class II hydrophobin NC2 and an engineered chimeric hydrophobin. These Class I hydrophobins form layers composed of laterally associated fibrils with an underlying amyloid structure. These two Class I hydrophobins, despite showing significant conformational differences in solution, self-assemble to form fibrillar layers with very similar structures and require a hydrophilic-hydrophobic interface to trigger self-assembly. Addition of additives that influence surface tension can be used to manipulate the fine structure of the protein films. The Class II hydrophobin NC2 forms a mesh-like protein network and the engineered chimeric hydrophobin displays two multimeric forms, depending on assembly conditions. When formed on a graphite surface, the fibrillar EAS_∆15 layers are resistant to alcohol, acid and basic washes. In contrast, the NC2 Class II monolayers are dissociated by alcohol treatment but are relatively stable towards acid and base washes. The engineered chimeric Class I/II hydrophobin shows increased stability towards alcohol and acid and base washes. Self-assembled hydrophobin films may have extensive applications in biotechnology where biocompatible; amphipathic coatings facilitate the functionalization of nanomaterials.

Surface pressure and elasticity of hydrophobin HFBII layers on the air-water interface: rheology versus structure detected by AFM imaging

Here, we combine experiments with Langmuir trough and atomic force microscopy (AFM) to investigate the reasons for the special properties of layers from the protein HFBII hydrophobin spread on the air-water interface. The hydrophobin interfacial layers possess the highest surface dilatational and shear elastic moduli among all investigated proteins. The AFM images show that the spread HFBII layers are rather inhomogeneous, (i.e., they contain voids, monolayer and multilayer domains). A continuous compression of the layer leads to filling the voids and transformation of a part of the monolayer into a trilayer. The trilayer appears in the form of large surface domains, which can be formed by folding and subduction of parts from the initial monolayer. The trilayer appears also in the form of numerous submicrometer spots, which can be obtained by forcing protein molecules out of the monolayer and their self-assembly into adjacent pimples. Such structures are formed because not only the hydrophobic parts, but also the hydrophilic parts of the HFBII molecules can adhere to each other in the water medium. If a hydrophobin layer is subjected to oscillations, its elasticity considerably increases, up to 500 mN/m, which can be explained with compaction. The relaxation of the layer's tension after expansion or compression follows the same relatively simple law, which refers to two-dimensional diffusion of protein aggregates within the layer. The characteristic diffusion time after compression is longer than after expansion, which can be explained with the impedence of diffusion in the more compact interfacial layer. The results shed light on the relation between the mesoscopic structure of hydrophobin interfacial layers and their unique mechanical properties that find applications for the production of foams and emulsions of extraordinary stability; for the immobilization of functional molecules at surfaces, and as coating agents for surface modification.