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

Abstract

Abstract: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. OPEN ACCESSNanomaterials 2014, 4 828

Exploring the frontiers of colloidal behaviour where polymers and particles meet

“…The hydrophobins are a unique class of small amphiphilic proteins (<10 kDa) possessing remarkable interfacial properties (Green, Littlejohn, Hooley, & Cox, 2013;Linder, 2009). At hydrophilicehydrophobic interfaces, the molecules spontaneously self-assemble into amphipathic layers based on fibrillar (class I) or non-fibrillar (class II) structures (Lo et al, 2014). The soluble class II hydrophobins are even more surface-active than the caseins, but, unlike the milk proteins, the molecules fully retain their folded native structure following adsorption at airewater and oilewater interfaces.…”

Marine fungi as source of new hydrophobins

“…Class I HFBs form highly insoluble aggregates that have the appearance of distinct rodlets and, similarly to amyloid fibrils, are characterized by cross β-structure [10]. These assemblies show outstanding stability and can be depolymerized in 100% trifluoroacetic acid (TFA) whereas class II HFBs form less stable polymers that are soluble in some organic solvents or SDS aqueous solution, and lack the rodlet appearance of class I HFBs [11]. Both types of HFBs have been used for several biotechnological applications, such as dispersion of hydrophobic materials, foam stabilization in food products, surface coating and modification of the surface wettability, immobilization of enzymes, peptides, antibodies and nanomaterials on various surfaces [12], [13], [14] and [15].The marine environment host a huge biodiversity of (micro) organisms, and fungi make up a large part of them [16].…”

Green synthesis of luminescent and defect-free bio-nanosheets of MoS2: interfacing two-dimensional crystals with hydrophobins

“…In their soluble form they show astonishingly high surface activity, indicated by the reduction of the surface tension of water and by a powerful emulsication capacity. 46,47 Moreover, upon adhesion onto various materials they can form nanostructured coatings, 48 able to revert the polarity of the surfaces, to mediate the non-covalent immobilization of a second layer of proteins, peptides and nanomaterials, 49,50 and to improve the stability and the biocompatibility of surfaces. 51,52 Class I HFBs are able to form chemically stable coatings composed of amyloid-like assemblies, named rodlets, which can be immunologically inert making them of great interest for the stable non-covalent functionalization of biomedical devices and nanodrugs.…”