Molecular Simulation of Hydrophobin Adsorption at an Oil-Water Interface
ABSTRACT Hydrophobins are small, amphiphilic proteins expressed by strains of filamentous fungi. They fulfill a number of biological functions, often related to adsorption at hydrophobic interfaces, and have been investigated for a number of applications in materials science and biotechnology. In order to understand the biological function and applications of these proteins, a microscopic picture of the adsorption of these proteins at interfaces is needed. Using molecular dynamics simulations with a chemically detailed coarse-grained potential, the behavior of typical hydrophobins at the water-octane interface is studied. Calculation of the interfacial adsorption strengths indicates that the adsorption is essentially irreversible, with adsorption strengths of the order of 100 k(B)T (comparable to values determined for synthetic nanoparticles but significantly larger than small molecule surfactants and biomolecules). The protein structure at the interface is unchanged at the interface, which is consistent with the biological function of these proteins. Comparison of native proteins with pseudoproteins that consist of uniform particles shows that the surface structure of these proteins has a large effect on the interfacial adsorption strengths, as does the flexibility of the protein.
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ABSTRACT: Hydrophobins, a class of highly surface active amphiphilic proteins, can stabilize various interfaces. When used for emulsion stabilization, it has been recently shown that they are able to induce mineralization, resulting in hollow capsules. We found that not all types of hydrophobins trigger mineralization, and that the morphology of the mineral changes depending on the selected oil. We investigated the formation of hydrophobin films at interfaces by the use of CD spectroscopy. In order to elucidate the structural features that enhance the mineralization property and give a possible explanation for this behavior, we performed MD-simulations of two representative hydrophobins (EAS for class I and HFBII for class II) at a hexane–water interface, in the presence as well as in the absence of ions. Our studies showed that the class II hydrophobin HFBII, which did not induce mineralization, only slightly changes its structure during adsorption at the oil–water interface or upon addition of Ca 2+ and HPO 4 2À ions. In contrast to that, the class I hydrophobin EAS changed its conformation to a large extent during the adsorption and interacted strongly with added ions. We revealed that EAS preorganizes the ions at short distances matching the lattice dimensions of hydroxyapatite. The latter finding yields a straightforward explanation for the observed differences in mineralization behavior and allows us to search for other hydrophobins that could assist mineralization, despite their different functions in nature.Soft Matter 01/2012; 8(44). DOI:10.1039/c2sm26428e · 4.15 Impact Factor
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ABSTRACT: By means of molecular dynamics simulations the free energy of adsorption of model dendrimer characterized by monomers of different chemical affinity is predicted as a function of the number and position of the monomers. The results show that modifying the affinity of the only end-monomers with one of the two solvent components (amphiphilic dendrimer) is enough to remarkably increase the stability of the molecule at the interface. The results also indicate that the so called Janus-dendrimer, where only half of the end-monomers are modified, does not show a higher interfacial stability compared with standard amphiphilic one. These findings compare well with simulation results obtained from atomistic simulations performed on polyaminoamide dendrimer at the air–water interface. The free energy profiles have also been compared with those obtained from simpler models which treat the dendrimer molecule as a rigid sphere showing that such simplification is acceptable in poor solvent but not in good solvent where the flexibility of the dendrimer molecule plays a major role in its stability at the interface. These calculations will help in the design of new amphiphilic dendrimers and in predicting their properties at liquid–liquid interface.Soft Matter 12/2012; 9(29):-. DOI:10.1039/C2SM27246F · 4.15 Impact Factor
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ABSTRACT: Class II hydrophobin (HFBII) is a very promising ingredient for improving foam stability. Pure HFBII-stabilized bubbles exhibited exceptional stability to disproportionation (dissolution) but were not stable to bubble coalescence induced by a pressure drop. Bubbles stabilized by mixtures of HFBII + sodium caseinate (SC) or -lactoglobulin (BL) showed decreased shrinkage rates compared to pure SC or BL and improved the stability to pressure drop induced coalescence. Higher bubble stability was more closely correlated with higher surface shear viscosity than the surface dilatational elasticity of the mixed protein systems. Brewster angle microscopy observations and the high shear strength of adsorbed films including HFBII, even in the presence of hydrophobic and hydrogen bond breaking agents, confirm that intermolecular attractive cross-links are unlikely to be the origin of the high strength of HFBII films. Possibly the HFBII molecules form a tightly interlocking monolayer of Janus-like particles at the air-water interface.Journal of Agricultural and Food Chemistry 01/2013; 61(7). DOI:10.1021/jf304603m · 3.11 Impact Factor