The major ampullate Spidroin 1 (MaSp1) is the main protein of the dragline spider silk. The C-terminal (CT) domain of MaSp1 is crucial for the self-assembly into fibers but the details of how it contributes to the fiber formation remain unsolved. Here we exploit the fact that the CT domain can form silk-like fibers by itself to gain knowledge about this transition. Structural investigations of fibers from recombinantly produced CT domain from E. australis MaSp1 reveal an α-helix to β-sheet transition upon fiber formation and highlight the helix No4 segment as most likely to initiate the structural conversion. This prediction is corroborated by the finding that a peptide corresponding to helix No4 has the ability of pH-induced conversion into β-sheets and self-assembly into nanofibrils. Our results provide structural information about the CT domain in fiber form and clues about its role in triggering the structural conversion of spidroins during fiber assembly.

The deposition of proteins in the form of amyloid fibrils is closely associated with several serious diseases. The events that trigger the conversion from soluble functional proteins into insoluble amyloid are not fully understood. Many proteins that are not associated with disease can form amyloid with similar structural characteristics as the disease-associated fibrils, which highlights the potential risk of cross-seeding of disease amyloid by amyloid-like structures encountered in our surrounding. Of particular interest are common food proteins that can be transformed into amyloid under conditions similar to cooking. We here investigate cross-seeding of amyloid-beta (A beta), a peptide known to form amyloid during the development of Alzheimer's disease, by 16 types of amyloid fibrils derived from food proteins or peptides. Kinetic studies using thioflavin T fluorescence as output show that none of the investigated protein fibrils accelerates the aggregation of A beta. In at least two cases (hen egg lysozyme and oat protein isolate) we observe retardation of the aggregation, which appears to originate from interactions between the food protein seeds and A beta in aggregated form. The results support the view that food-derived amyloid is not a risk factor for development of A beta pathology and Alzheimer's disease.

Furan-based polymers are renewable alternatives for traditional fossil-based polymers, therefore carrying enormous potential for improved sustainability. Many aspects of these novel polymers still need to be investigated more comprehensively for full appreciation of their applicability. Here, the degradation of furan-based polymers including poly(butylene furanoate), poly(butylene bifuranoate), and three random copolyesters thereof were investigated under artificial weathering conditions for up to 300 h. This included simultaneous exposure of film samples to ultraviolet light, high humidity, and elevated temperature. Poly(ethylene terephthalate) was used as a reference material. Both the pristine and weathered samples were characterized using infrared spectroscopy, differential scanning calorimetry, and dynamic mechanical analysis, among others. According to the infrared measurements, the exposed surfaces of the films had undergone severe chemical changes. Indications of covalent cross-linking after exposure to ultraviolet light were found in differential scanning calorimetry, dynamic mechanical analysis, and dissolution experiments. The nature of the cross-linking mechanisms and exact structure of the formed degradation products remain unclear. It is concluded that polyesters derived from both 2,5-furandicarboxylic and 2,2 '-bifuran-5,5 '-dicarboxylic acids are relatively labile when exposed to UV light. The latter monomer appears especially labile, probably in part because of its broader and elevated UV absorbance. Simple oven-aging in air indicated that crosslinking also occurred in the absence of UV, but the overall chemical degradation was stronger in the weathering conditions. In the more easily crystallizable samples, the aging-induced crystallization played an important role in the final physical properties.

Covalently crosslinked protein networks produced from whey protein nanofibrils (PNFs) are demonstrated to be sustainable high‐performance foams that show chemical resistance and mechanical strength, stiffness, and toughness on harsh aging at 150 °C. The aged foams are able to retain their properties at 180 °C for as long as 24 h, far exceeding the properties of most classical petroleum‐based thermoplastics. The foams are further developed into soft foams by the addition of glycerol as a plasticizer. The improvement in the mechanical performance of the foams with aging, which is equivalent to an increase by one order of magnitude in modulus and yield strength, is confirmed to be associated with (iso)peptide crosslinks. The results open the way for using protein‐based foam materials in severe/corrosive environments such as filtration, thermal insulation, and fluid absorption. The protein foams produced are suggested as suitable alternatives to petroleum‐based porous polymers.

The plant cuticle is a hydrophobic barrier membrane found mainly on leaf surfaces and fruit skin. This work presents the structural and barrier properties of cuticle-inspired poly(hydroxyhexadecanoate) (PHHA), an omega-hydroxy fatty acid-derived biopolyester. PHHA was copolymerized and cross-linked with glycerol by melt polycondensation, and films were fabricated by compression molding. The study showed the effect of the addition of a trifunctional comonomer on the thermal, mechanical, and barrier properties. The neat PHHA, owing to its higher crystallinity, demonstrated the best water vapor barrier properties, but formed brittle films. The glycerol-copolymerized films, on the other hand, were flexible and displayed a good balance between barrier and mechanical properties. The water vapor transmission rate was overall similar to that of PLA, and limonene (a hydrophobic food component) uptake and diffusivity were lower than that of low-density polyethylene, the commonly used polymer for packaging. In addition, the polyester had UV-blocking properties. The way the films were made yielded a rough surface, mimicking the outer rough wax layer in plant cuticles with high water repellence. Hence, these cutin-inspired polyesters are promising for, e.g., water barrier (packaging/device) applications, provided means of efficient/sustainable production/isolation of the monomer is developed.

Protein nanofibrils (PNFs) represent a promising class of biobased nanomaterials for biomedical and materials science applications. In the design of such materials, a fundamental understanding of the structure-function relationship at both molecular and nanoscale levels is essential. Here we report investigations of the nanoscale morphology and molecular arrangement of amyloid-like PNFs of a synthetic peptide fragment consisting of residues 11-20 of the protein beta-lactoglobulin (beta-LG(11-20)), an important model system for PNF materials. Nanoscale fibril morphology was analysed by atomic force microscopy (AFM) that indicates the presence of polymorphic self-assembly of protofilaments. However, observation of a single set of C-13 and N-15 resonances in the solid-state NMR spectra for the beta-LG(11-20) fibrils suggests that the observed polymorphism originates from the assembly of protofilaments at the nanoscale but not from the molecular structure. The secondary structure and inter-residue proximities in the beta-LG(11-20) fibrils were probed using NMR experiments of the peptide with C-13- and N-15-labelled amino acid residues at selected positions. We can conclude that the peptides form parallel beta-sheets, but the NMR data was inconclusive regarding inter-sheet packing. Molecular dynamics simulations confirm the stability of parallel beta-sheets and suggest two preferred modes of packing. Comparison of molecular dynamics models with NMR data and calculated chemical shifts indicates that both packing models are possible.

The rich pool of protein conformations combined with the dimensions and properties of carbon nanotubes create new possibilities in functional materials and nanomedicine. Here, the intrinsically disordered protein α-synuclein is explored as a dispersant of single-walled carbon nanotubes (SWNTs) in water. We use a range of spectroscopic methods to quantify the amount of dispersed SWNT and to elucidate the binding mode of α-synuclein to SWNT. The dispersion ability of α-synuclein is good even with mild sonication and the obtained dispersion is very stable over time. The whole polypeptide chain is involved in the interaction accompanied by a fraction of the chain changing into a helical structure upon binding. Similar to other dispersants, we observe that only a small fraction (15–20%) of α-synuclein is adsorbed on the SWNT surface with an average residence time below 10 ms