Class I hydrophobins are a unique family of fungal proteins that form a polymeric, water-repellent monolayer on the surface of structures such as spores and fruiting bodies. Similar monolayers are being discovered on an increasing range of important microorganisms. Hydrophobin monolayers are amphipathic and particularly robust, and they reverse the wettability of the surface on which they are formed. There are also significant similarities between these polymers and amyloid-like fibrils. However, structural information on these proteins and the rodlets they form has been elusive. Here, we describe the three-dimensional structure of the monomeric form of the class I hydrophobin EAS. EAS forms a ␤-barrel structure punctuated by several disordered regions and displays a complete segregation of charged and hydrophobic residues on its surface. This structure is consistent with its ability to form an amphipathic polymer. By using this structure, together with data from mutagenesis and previous biophysical studies, we have been able to propose a model for the polymeric rodlet structure adopted by these proteins. X-ray fiber diffraction data from EAS rodlets are consistent with our model. Our data provide molecular insight into the nature of hydrophobin rodlet films and extend our understanding of the fibrillar ␤-structures that continue to be discovered in the protein world. amyloid ͉ NMR ͉ polymer H ydrophobins are a large family of secreted, low-molecularmass (7-9 kDa) proteins unique to filamentous fungi. There is little amino acid sequence similarity between hydrophobins, except for a characteristic pattern of eight cysteine residues that form four intramolecular disulfide bonds (1, 2). These proteins have remarkable biophysical properties and function by selfassembling into amphipathic polymeric films at the interface between hydrophobic and hydrophilic surfaces (3). The surfactive and amphipathic properties of hydrophobins facilitate the formation of essential aerial structures such as hyphae, spores, and fruiting bodies (4).Two classes of hydrophobins have been identified based on their hydrophobicity plots and physical properties (5). For class I hydrophobins, the polymer film comprises cylindrical rodlets with dimensions of Ϸ10 ϫ 100-250 nm and their outward-facing hydrophobic surface has extremely low wettability (6, 7). These films are very robust; they are resistant to boiling in detergents or strong alkalis (8, 9). The morphology of isolated rodlets is reminiscent of amyloid fibrils isolated from diseased tissue and formed in vitro. Reconstituted rodlets stained with Congo red give the green-gold birefringence characteristic of similarly stained amyloid fibers and circular dichroism (CD) data indicate that the rodlets contain extensive ␤-structure, suggesting that rodlets and amyloid fibrils have structural features in common (10, 11, **). Class II hydrophobin films are significantly less robust and lack the rodlet morphology of class I hydrophobins (12, 13).Class I hydrophobins, once solubilized, will spo...

Hydroponic plant growth studies indicate that silver nanoparticles (Ag NPs) are phytotoxic. In this work, the phytotoxicity of commercial Ag NPs (10 nm) was evaluated in a sand growth matrix. Both NPs and soluble Ag were recovered from water extracts of the sand after growth of plants challenged with the commercial product; the surface charge of the Ag NPs in this extract was slightly reduced compared to the stock NPs. The Ag NPs reduced the length of shoots and roots of wheat in a dose-dependent manner. Furthermore, 2.5 mg/kg of the NPs increased branching in the roots of wheat (Triticum aestivum L.), thereby affecting plant biomass. Micron-sized (bulk) Ag particles (2.5 mg/kg) as well as Ag ions (63 μg Ag/kg) equivalent to the amount of soluble Ag in planted sand with Ag NPs (2.5 mg/kg) did not affect plant growth compared to control. In contrast, higher levels of Ag ions (2.5 mg/kg) reduced plant growth to a similar extent as the Ag NPs. Accumulation of Ag was detected in the shoots, indicating an uptake and transport of the metal from the Ag NPs in the sand. Transmision electron microscopy indicated that Ag NPs were present in shoots of plants with roots exposed to the Ag NPs or high levels of Ag ions. Both of these treatments caused oxidative stress in roots, as indicated by accumulation of oxidized glutathione, and induced expression of a gene encoding a metallothionein involved in detoxification by metal ion sequestration. Our findings demonstrate the potential effects of environmental contamination by Ag NPs on the metabolism and growth of food crops in a solid matrix.

Electrocatalytic IrO 2 -RuO 2 supported on Sb-doped SnO 2 (ATO) nanoparticles is very active towards the oxygen evolution reaction. The IrO 2 -RuO 2 material is XRD amorphous and exists as clusters on the surface of the ATO.Systematic changes to the surface chemical composition of the ATO as a function of the IrO 2 :RuO 2 ratio suggests an interaction between the IrO 2 -RuO 2 and ATO. Cyclic voltammetry indicates that the electrochemically active surface area of IrO 2 -RuO 2 clusters is maximised when the composition is 75 mol% IrO 2 -25 mol% RuO 2 . Decreasing the loading of IrO 2 -RuO 2 on ATO reduces the electrochemically active surface area, although there is evidence to support a decrease in the clusters size with decreased loading. Tafel slope analysis shows that if the clusters are too small, the kinetics of the oxygen evolution reaction are reduced. Overall, clusters of IrO 2 -RuO 2 on ATO have similar or better performance for the oxygen evolution reaction than many previously reported materials, despite the low quantity of noble metals used in the electrocatalysts. This suggests that these oxides may be of economic

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EAS joins an increasing number of proteins that undergo a disorder-->order transition in carrying out their normal function. This report is one of the few examples where an amyloid-like state represents the wild-type functional form. Thus the mechanism of amyloid formation, now thought to be a general property of polypeptide chains, has actually been applied in nature to form these remarkable structures.