Structural basis for the formation of soy protein nanofibrils

Type I Hsp40s/DnaJs aggregates exhibit features reminiscent of amyloidogenic structures

A rise in temperature triggers a structural change in the human Type I 40 kDa heat shock protein (Hsp40/DnaJ), known as DNAJA1. This change leads to a less compact structure, characterized by an increased presence of solvent-exposed hydrophobic patches and β-sheet-rich regions. This transformation is validated by circular dichroism, thioflavin T binding, and Bis-ANS assays. The formation of this β-sheet-rich conformation, which is amplified in the absence of zinc, leads to protein aggregation. This aggregation is induced not only by high temperatures but also by low ionic strength and high protein concentration. The aggregated conformation exhibits characteristics of an amyloidogenic structure, including a distinctive X-ray diffraction pattern, seeding competence (which stimulates the formation of amyloid-like aggregates), cytotoxicity, resistance to SDS, and fibril formation. Interestingly, the yeast Type I Ydj1 also tends to adopt a similar β-sheet-rich structure under comparable conditions, whereas Type II Hsp40s, whether human or from yeast, do not. Moreover, Ydj1 aggregates were found to be cytotoxic. Studies using DNAJA1- and Ydj1-deleted mutants suggest that the zinc-finger region plays a crucial role in amyloid formation. Our discovery of amyloid aggregation in a C-terminal deletion mutant of DNAJA1, which resembles a spliced homolog expressed in the testis, implies that Type I Hsp40 co-chaperones may generate amyloidogenic species in vivo.

In Situ Nanoencapsulation of Curcumin in Soy Protein Isolate Amyloid-like Aggregates for Enhanced Wound Healing

The importance of amyloid nanofibrils made from food proteins is rising in diverse fields, such as biomedicine and food science. These protein nanofibrils (PNFs) serve as versatile and sustainable building blocks for biomaterials, characterized by their high β-sheet content and an ordered hydrogen bond network. These properties offer both stability and flexibility, along with an extreme aspect ratio and reactive functional groups. Plant-derived amyloid nanofibrils, such as soy protein isolate (SPI) PNFs, are increasingly favored due to their affordability and sustainability compared with animal proteins. This study aimed to explore the formation and application of SPI amyloid-like aggregates (SPIA) and their nanoencapsulation of curcumin (Cur) for biomedical purposes, particularly in wound healing. Under specific conditions of low pH and high temperature, SPIA formed, exhibited an amyloid nature, and successfully encapsulated Cur, thereby enhancing its stability and availability. Spectroscopic and microscopic analyses confirmed structural changes in SPIA upon the incorporation of Cur and the fabrication of SPIA@Cur. The obtained results indicate that in the presence of Cur, SPIA forms faster, attributed to accelerated SPI denaturation, an increased nucleation rate, and enhanced self-assembly facilitated by Cur's hydrophobic interactions and π-π stacking with SPI peptides. In vitro studies demonstrated the biocompatibility, biodegradability, and antioxidant properties of SPIA@Cur along with controlled release behavior. In vivo experiments in male Wistar rats revealed that both SPIA and SPIA@Cur significantly accelerate wound closure compared with untreated wounds, with SPIA@Cur showing slightly better efficacy. The histological analysis supported enhanced wound healing, indicating the potential of SPIA@Cur for biomedical applications.

Peptide Supramolecular Self-Assembly: Regulatory Mechanism, Functional Properties, and Its Application in Foods

Peptide self-assembly, due to its diverse supramolecular nanostructures, excellent biocompatibility, and bright application prospects, has received wide interest from researchers in the fields of biomedicine and green life technology and the food industry. Driven by thermodynamics and regulated by dynamics, peptides spontaneously assemble into supramolecular structures with different functional properties. According to the functional properties derived from peptide self-assembly, applications and development directions in foods can be found and explored. Therefore, in this review, the regulatory mechanism is elucidated from the perspective of self-assembly thermodynamics and dynamics, and the functional properties and application progress of peptide self-assembly in foods are summarized, with a view to more adaptive application scenarios of peptide self-assembly in the food industry.

Wheat flour-derived amyloid fibrils for efficient removal of organic dyes from contaminated water

Amyloid fibrils derived from different proteins have been proved as a promising material for adsorption of various pollutants from wastewater, which showed advantages of low cost and eco-friendliness. However, most of the amyloid fibrils derived from animal-based proteins with high environmental footprint, while more sustainable amyloid fibrils derived from plant materials are desirable. In this study, a plant-derived amyloid fibril was extracted from the commonly used wheat flour with a simple and scalable protein purification and fibrillization process. Interestingly, the amyloid fibrils showed good adsorption capacity towards typical organic dyes (Eosin Y (EY) and Congo red (CR)) from contaminated water. Adsorption kinetic analysis indicated the adsorption process to EY or CR by wheat flour amyloid well fitted with a pseudo-second-order model. The adsorption also followed a Langmuir isothermal model with adsorption capacities of 333 mg/g and 138 mg/g towards CR and EY, respectively. This work demonstrated the feasibility to utilize the plant-based amyloid fibril for organic dyes removal from contaminated water, which provided an affordable, sustainable and scalable tool for organic dyes removal from wastewater.

From Fundamental Amyloid Protein Self-Assembly to Development of Bioplastics

Proteins can self-assemble into a range of nanostructures as a result of molecular interactions. Amyloid nanofibrils, as one of them, were first discovered with regard to the relevance of neurodegenerative diseases but now have been exploited as building blocks to generate multiscale materials with designed functions for versatile applications. This review interconnects the mechanism of amyloid fibrillation, the current approaches to synthesizing amyloid protein-based materials, and the application in bioplastic development. We focus on the fundamental structures of self-assembled amyloid fibrils and how external factors can affect protein aggregation to optimize the process. Protein self-assembly is essentially the autonomous congregation of smaller protein units into larger, organized structures. Since the properties of the self-assembly can be manipulated by changing intrinsic factors and external conditions, protein self-assembly serves as an excellent building block for bioplastic development. Building on these principles, general processing methods and pathways from raw protein sources to mature state materials are proposed, providing a guide for the development of large-scale production. Additionally, this review discusses the diverse properties of protein-based amyloid nanofibrils and how they can be utilized as bioplastics. The economic feasibility of the protein bioplastics is also compared to conventional plastics in large-scale production scenarios, supporting their potential as sustainable bioplastics for future applications.

Nordic Crops as Alternatives to Soy-An Overview of Nutritional, Sensory, and Functional Properties

Soy (Glycine max) is used in a wide range of products and plays a major role in replacing animal-based products. Since the cultivation of soy is limited by cold climates, this review assessed the nutritional, sensory, and functional properties of three alternative cold-tolerant crops (faba bean (Vicia faba), yellow pea (Pisum sativum), and oat (Avena sativa)). Lower protein quality compared with soy and the presence of anti-nutrients are nutritional problems with all three crops, but different methods to adjust for these problems are available. Off-flavors in all pulses, including soy, and in cereals impair the sensory properties of the resulting food products, and few mitigation methods are successful. The functional properties of faba bean, pea, and oat are comparable to those of soy, which makes them usable for 3D printing, gelation, emulsification, and extrusion. Enzymatic treatment, fermentation, and fibrillation can be applied to improve the nutritional value, sensory attributes, and functional properties of all the three crops assessed, making them suitable for replacing soy in a broad range of products, although more research is needed on all attributes.

Morphology, Formation Kinetics and Core Composition of Pea and Soy 7S and 11S Globulin Amyloid Fibrils

Legume seed storage proteins can be induced to form amyloid fibrils upon heating at low pH, which could improve their functionality for use in food and materials. However, the amyloidogenic regions of legume proteins are largely unknown. Here, we used LC-MS/MS to determine the amyloid core regions of fibrils formed by enriched pea and soy 7S and 11S globulins at pH 2, 80 °C, and characterized their hydrolysis, assembly kinetics, and morphology. A lag phase was absent from the fibrillation kinetics of pea and soy 7S globulins, while 11S globulins and crude extracts displayed a similar lag time. Pea and soy protein fibrils differed in morphology, with most pea fibrils being straight and soy fibrils being worm-like. Pea and soy globulins were abundant in amyloid-forming peptides, with over 100 unique fibril-core peptides from pea 7S and around 50 unique fibril-core peptides identified from pea 11S, soy 7S, and soy 11S globulins. Amyloidogenic regions derive predominantly from the homologous core region of 7S globulins and the basic subunit of 11S globulins. Overall, pea and soy 7S and 11S globulins are rich in amyloidogenic regions. This study will help understand their fibrillation mechanism and engineer protein fibrils with specific structures and functionality.

Food protein-derived amyloids do not accelerate amyloid β aggregation

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-β (Aβ), 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 Aβ. 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 Aβ in aggregated form. The results support the view that food-derived amyloid is not a risk factor for development of Aβ pathology and Alzheimer's disease.

Effects of ultrasound pretreatment on functional property, antioxidant activity, and digestibility of soy protein isolate nanofibrils

Nanofibrils, an effective method to modulate the functional properties of proteins, can be promoted by ultrasound pretreatment. This study investigated the effect of ultrasound pretreatment on the structure, functional property, antioxidant activity and digestibility of soy protein isolate (SPI) nanofibrils. The results showed that high amplitude ultrasound had a significant effect on structure of SPI nanofibrils. SPI nanofibrils pretreated by 80% amplitude ultrasound showed a blueshift of the amide II band in Fourier transform infrared spectroscopy (FTIR), resulted in more tryptophan residues being buried and increased the crystallinity. Low amplitude ultrasound (20%) pretreatment significantly improved the solubility, emulsifying activity index (EAI) and water absorption capacity (WAC) of SPI nanofibrils, but 80% amplitude ultrasound pretreatment of SPI nanofibrils reduced emulsifying stability index (ESI). High amplitude ultrasound (60% and 80%) pretreatment of SPI nanofibrils improved the foaming capacity and foaming stability and decreased denaturation temperature. DPPH radical scavenging activity of SPI nanofibrils were significantly improved by ultrasound pretreatment. 20% amplitude ultrasound pretreatment improved DPPH, ABTS radical scavenging activity and ferric reducing antioxidant power of SPI nanofibrils. The digestion rate of 80% amplitude ultrasound-pretreated nanofibrils were consistently higher, and SPI nanofibrils pretreated by ultrasound were more fragmented and shorter after simulating gastrointestinal digestion. This study would expand the application of food-grade protein nanofibrils in the food industry.

Nanofibrils of food-grade proteins: Formation mechanism, delivery systems, and application evaluation

Due to the high aspect ratio, appealing mechanical characteristics, and various adjustable functional groups on the surface proteins, food-grade protein nanofibrils have attracted great research interest in the field of food science. Fibrillation, known as a process of peptide self-assembly, is recognized as a common attribute for food-grade proteins. Converting food-grade proteins into nanofibrils is a promising strategy to broaden their functionality and applications, such as improvement of the properties of gelling and emulsifying, especially for constructing various delivery systems for bioactive compounds. Protein source and processing conditions have a great impact on the size, structure, and morphology of nanofibrils, resulting in extreme differences in functionality. With this feature, it is possible to engineer nanofibrils into four different delivery systems, including gels, microcapsules, emulsions, and complexes. Construction of nanofibril-based gels via multiple cross-linking methods can endow gels with special network structures to efficiently capture bioactive compounds and extra mechanical behavior. The adsorption behavior of nanofibrils at the interface is highly complex due to the influence of several intrinsic factors, which makes it challenging to form stabilized nanofibril-based emulsion systems. Based on electrostatic interactions, microcapsules and complexes prepared using nanofibrils and polysaccharides have combined functional properties, resulting in adjustable release behavior and higher encapsulation efficiency. The bioactive compounds delivery system based on nanofibrils is a potential solution to enhance their absorption in the gastrointestinal tract, improve their bioavailability, and deliver them to target organs. Although food-grade protein nanofibrils show unknown toxicity to humans, further research can contribute to broadening the application of nanofibrils in delivery systems.

Investigating the Sequence Determinants of the Curling of Amyloid Fibrils Using Ovalbumin as a Case Study

Highly ordered, straight amyloid fibrils readily lend themselves to structure determination techniques and have therefore been extensively characterized. However, the less ordered curly fibrils remain relatively understudied, and the structural organization underlying their specific characteristics remains poorly understood. We found that the exemplary curly fibril-forming protein ovalbumin contains multiple aggregation prone regions (APRs) that form straight fibrils when isolated as peptides or when excised from the full-length protein through hydrolysis. In the context of the intact full-length protein, however, the regions separating the APRs facilitate curly fibril formation. In fact, a meta-analysis of previously reported curly fibril-forming proteins shows that their inter-APRs are significantly longer and more hydrophobic when compared to straight fibril-forming proteins, suggesting that they may cause strain in the amyloid state. Hence, inter-APRs driving curly fibril formation may not only apply to our model protein but rather constitute a more general mechanism.

Robust Assembly of Cross-Linked Protein Nanofibrils into Hierarchically Structured Microfibers

Natural, high-performance fibers generally have hierarchically organized nanosized building blocks. Inspired by this, whey protein nanofibrils (PNFs) are assembled into microfibers, using flow-focusing. By adding genipin as a nontoxic cross-linker to the PNF suspension before spinning, significantly improved mechanical properties of the final fiber are obtained. For curved PNFs, with a low content of cross-linker (2%) the fiber is almost 3 times stronger and 4 times stiffer than the fiber without a cross-linker. At higher content of genipin (10%), the elongation at break increases by a factor of 2 and the energy at break increases by a factor of 5. The cross-linking also enables the spinning of microfibers from long straight PNFs, which has not been achieved before. These microfibers have higher stiffness and strength but lower ductility and toughness than those made from curved PNFs. The fibers spun from the two classes of nanofibrils show clear morphological differences. The study demonstrates the production of protein-based microfibers with mechanical properties similar to natural protein-based fibers and provides insights about the role of the nanostructure in the assembly process.

Clustering and cross-linking of the wheat storage protein α-gliadin: A combined experimental and theoretical approach

Our aim was to understand mechanisms for clustering and cross-linking of gliadins, a wheat seed storage protein type, monomeric in native state, but incorporated in network while processed. The mechanisms were studied utilizing spectroscopy and high-performance liquid chromatography on a gliadin-rich fraction, in vitro produced α-gliadins, and synthetic gliadin peptides, and by coarse-grained modelling, Monte Carlo simulations and prediction algorithms. In solution, gliadins with α-helix structures (dip at 205 nm in CD) were primarily present as monomeric molecules and clusters of gliadins (peaks at 650- and 700-s on SE-HPLC). At drying, large polymers (R_g 90.3 nm by DLS) were formed and β-sheets increased (14% by FTIR). Trained algorithms predicted aggregation areas at amino acids 115-140, 150-179, and 250-268, and induction of liquid-liquid phase separation at P- and Poly-Q-sequences (Score = 1). Simulations showed that gliadins formed polymers by tail-to-tail or a hydrophobic core (Kratky plots and R_ee = 35 and 60 for C- and N-terminal). Thus, the N-terminal formed clusters while the C-terminal formed aggregates by disulphide and lanthionine bonds, with favoured hydrophobic clustering of similar/exact peptide sections (synthetic peptide mixtures on SE-HPLC). Mechanisms of clustering and cross-linking of the gliadins presented here, contribute ability to tailor processing results, using these proteins.

Homogeneous nuclei-induced, secondary nuclei-induced, and spontaneous whey protein concentrate nanofibril formation through different pathways

The addition of homogeneous nuclei (HN) or secondary nuclei (SN) could lead to different kinetics and thermodynamics as the nucleation energy barrier decreases and the lag time is shortened to different degrees compared with spontaneous fibrillation. To explain these differences, we monitored the formation and depletion of HN during fibril formation and found that both SN-induced fibrils and HN-induced fibrils follow the same nucleated growth pathway as spontaneously formed WPC fibrils. Moreover, there were also other paths, which were confirmed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy. The surfaces of the SN could recruit monomers and resulted in stronger intersheet stacking and a larger fibril height and periodicity. The HN incorporation led to a propensity for hydrogen-bonding interactions and a longer fibril. Fibrillation by the addition HN and SN followed both common and distinct pathways, as spontaneous fibrillation and led to different capacities to induce fibrillation.

Protein nanofibrils and their use as building blocks of sustainable materials

The development towards a sustainable society requires a radical change of many of the materials we currently use. Besides the replacement of plastics, derived from petrochemical sources, with renewable alternatives, we will also need functional materials for applications in areas ranging from green energy and environmental remediation to smart foods. Proteins could, with their intriguing ability of self-assembly into various forms, play important roles in all these fields. To achieve that, the code for how to assemble hierarchically ordered structures similar to the protein materials found in nature must be cracked. During the last decade it has been demonstrated that amyloid-like protein nanofibrils (PNFs) could be a steppingstone for this task. PNFs are formed by self-assembly in water from a range of proteins, including plant resources and industrial side streams. The nanofibrils display distinct functional features and can be further assembled into larger structures. PNFs thus provide a framework for creating ordered, functional structures from the atomic level up to the macroscale. This review address how industrial scale protein resources could be transformed into PNFs and further assembled into materials with specific mechanical and functional properties. We describe what is required from a protein to form PNFs and how the structural properties at different length scales determine the material properties. We also discuss potential chemical routes to modify the properties of the fibrils and to assemble them into macroscopic structures.

Controlled self-assembly of plant proteins into high-performance multifunctional nanostructured films

The abundance of plant-derived proteins, as well as their biodegradability and low environmental impact make them attractive polymeric feedstocks for next-generation functional materials to replace current petroleum-based systems. However, efforts to generate functional materials from plant-based proteins in a scalable manner have been hampered by the lack of efficient methods to induce and control their micro and nanoscale structure, key requirements for achieving advantageous material properties and tailoring their functionality. Here, we demonstrate a scalable approach for generating mechanically robust plant-based films on a metre-scale through controlled nanometre-scale self-assembly of water-insoluble plant proteins. The films produced using this method exhibit high optical transmittance, as well as robust mechanical properties comparable to engineering plastics. Furthermore, we demonstrate the ability to impart nano- and microscale patterning into such films through templating, leading to the formation of hydrophobic surfaces as well as structural colour by controlling the size of the patterned features.