Conformable self-assembling amyloid protein coatings with genetically programmable functionality

Interfacial engineering for biomolecule immobilisation in microfluidic devices

Microfluidic devices are used for various applications in biology and medicine. From on-chip modelling of human organs for drug screening and fast and straightforward point-of-care (POC) detection of diseases to sensitive biochemical analysis, these devices can be custom-engineered using low-cost techniques. The microchannel interface is essential for these applications, as it is the interface of immobilised biomolecules that promote cell capture, attachment and proliferation, sense analytes and metabolites or provide enzymatic reaction readouts. However, common microfluidic materials do not facilitate the stable immobilisation of biomolecules required for relevant applications, making interfacial engineering necessary to attach biomolecules to the microfluidic surfaces. Interfacial engineering is performed through various immobilisation mechanisms and surface treatment techniques, which suitably modify the surface properties like chemistry and energy to obtain robust biomolecule immobilisation and long-term storage stability suitable for the final application. In this review, we provide an overview of the status of interfacial engineering in microfluidic devices, covering applications, the role of biomolecules, their immobilisation pathways and the influence of microfluidic materials. We then propose treatment techniques to optimise performance for various biological and medical applications and highlight future areas of development.

Amyloid Fibrils and Their Applications: Current Status and Latest Developments

Amyloid fibrils are one of the important forms of protein aggregates, first discovered in the pathological brain tissues of patients with various neurodegenerative diseases. They are considered the core pathological markers of different neurodegenerative diseases. In recent years, research has found that multiple proteins or peptides dynamically assemble to form functional amyloid-like nanofibrils under physiological conditions, exhibiting excellent mechanical properties, high environmental stability, and self-healing ability. Therefore, they have become a class of functional biological nanomaterials with important development potential. This article systematically reviews the latest progress in the preparation, functionalization, and application of amyloid-like nanofibrils in engineering and provides an outlook on possible future development directions.

Amyloids in bladder cancer hijack cancer-related proteins and are positive correlated to tumor stage

Despite the current diagnostic and therapeutic approaches to bladder cancer being widely accepted, there have been few significant advancements in this field over the past decades. This underscores the necessity for a paradigm shift in the approach to bladder cancer. The role of amyloids in cancer remains unclear despite their identification in several other pathologies. In this study, we present evidence of amyloids in bladder cancer, both in vitro and in vivo. In a murine model of bladder cancer, a positive correlation was observed between amyloids and tumor stage, indicating an association between amyloids and bladder cancer progression. Subsequently, the amyloid proteome of the RT4 non-invasive and HT1197 invasive bladder cancer cell lines was identified and included oncogenes, tumor suppressors, and highly expressed cancer-related proteins. It is proposed that amyloids function as structures that sequester key proteins. Therefore, amyloids should be considered in the study and diagnosis of bladder cancer.

Coating of Threads with Fluorescent Curli Fibers for pH Sensing

Threads coated with bioresponsive materials hold promise for innovative wearable diagnostics. However, most thread coatings reported so far cannot be easily customized for different analytes and frequently incorporate non-biodegradable components. Most optically active thread coatings rely on dyes, which often exhibit irreversible responses. In this work, we propose a biosensing coating for threads using curli fibers. Curli fibers are self-assembling fibers of the protein CsgA that can be genetically engineered to sense rapidly evolving diagnostic targets. We first established a simple electrostatic-mediated absorption protocol for coating anionic cotton threads with anionic curli fibers using an intervening cationic chitosan layer. We applied this protocol to two types of pH-sensing curli fibers, displaying either fluorescent pHuji or mCitrine proteins. This process ensures extensive curli coating over the entire thread surface using only water-based solvents. The resulting protein-coated threads are moderately hydrophobic, stretchable, and can monitor pH changes in real time through fluorescence. The coatings are also stable and functional on the surface for over 25 cycles of use, highlighting their potential for reusable practical applications. This straightforward and adaptable protocol can be extended to coat threads with diverse sensing and responsive capabilities for intelligent clothing.

Self-Assembly of Microstructured Protein Coatings with Programmable Functionality for Fluorescent Biosensors

Proteins, as genetically programmable functional macromolecules, hold immense potential as biocompatible self-assembling building blocks, owing to their versatility in building coating materials and programming their functionality genetically. In this study, we demonstrate a modular self-assembly of protein coatings that are genetically programmable for a biosensor application. We designed and produced recombinant fusion protein building blocks to form microstructured coatings on diverse substrates, such as glass or polymers, through thermally triggered liquid-liquid phase separation and an orthogonal high-affinity coiled-coil interaction. We incorporated fluorescence proteins into coatings and controlled the protein density to enable fluorescence imaging and quantification in a low-resource setting. Then, we created a coating for a calcium biosensor using a genetically engineered calcium indicator protein. This protein coating served as the foundation for our smartphone-based fluorescent biosensor, which successfully measured free calcium concentrations in the millimolar range at which extracellular calcium homeostasis is maintained. Using this fluorescent biosensor, we were able to detect abnormal physiological conditions, such as mild or moderate hypercalcemia. We envision that this modular and genetically programmable functional protein coating platform could be extended to the development of highly accessible, low-cost fluorescent biosensors for a variety of targets.

A Self-Assembling γPFD-SpyCatcher Hydrogel Scaffold for the Coimmobilization of SpyTag-Enzymes to Facilitate the Catalysis of Regulated Enzymes

In this study, a γPFD-SpyCatcher hydrogel scaffold with the capacity for spontaneous assembly was established. With a maximum loading capacity of a 1:1 molar ratio with SpyTag-enzymes, the immobilized proteins can not only rapidly provide pure enzymes but also exhibit improved thermal and pH stability. The results of the transmission electron microscopic analysis and the traits they present indicated that SpyCatcher promotes the aggregation of γPFD and the formation of hydrogels. In the cell-free pyruvate synthesis system, the γPFD-SpyCatcher coimmobilized SpyTag-hexokinase (HK), SpyTag-phosphofructokinase (PFK) and SpyTag-pyruvate kinase (PK) were employed, and the production of pyruvate increased by 43, 78 and 47% respectively. In in vitro experiments, the oxidative deamination activity of glutamate dehydrogenase (GDH) coimmobilized with γPFD-SpyCatcher was 38% higher than that of purified enzymes. These findings indicate that the γPFD-SpyCatcher-based hydrogels play an important role in breaking the barrier of regulatory enzymes and will provide more strategies for the development of synthetic biology.

Conformal and conductive biofilm-bridged artificial Z-scheme system for visible light-driven overall water splitting

Semi-artificial Z-scheme systems offer promising potential toward efficient solar-to-chemical conversion, yet sustainable and stable designs are currently lacking. Here, we developed a sustainable hybrid Z-scheme system capable for visible light-driven overall water splitting by integrating the durability of inorganic photocatalysts with the interfacial adhesion and regenerative property of bacterial biofilms. The Z-scheme configuration is fabricated by drop casting a mixture of photocatalysts onto a glass plate, followed by the growth of biofilms for conformal conductive paste through oxidative polymerization of pyrrole molecules. Notably, the system exhibited scalability indicated by consistent catalytic efficiency across various sheet areas, resistance observed by remarkable maintaining of photocatalytic efficiency across a range of background pressures, and high stability as evidenced by minimal decay of photocatalytic efficiency after 100-hour reaction. Our work thus provides a promising avenue toward sustainable and high-efficiency artificial photosynthesis, contributing to the broader goal of sustainable energy solutions.

Extracellular Matrix-Mimetic Intrinsic Versatile Coating Derived from Marine Adhesive Protein Promotes Diabetic Wound Healing through Regulating the Microenvironment

The management of diabetic wound healing remains a severe clinical challenge due to the complicated wound microenvironments, including abnormal immune regulation, excessive reactive oxygen species (ROS), and repeated bacterial infections. Herein, we report an extracellular matrix (ECM)-mimetic coating derived from scallop byssal protein (Sbp9Δ), which can be assembled in situ within 30 min under the trigger of Ca2+ driven by strong coordination interaction. The biocompatible Sbp9Δ coating and genetically programmable LL37-fused coating exhibit outstanding antioxidant, antibacterial, and immune regulatory properties in vitro. Proof-of-concept applications demonstrate that the coating can reliably promote wound healing in animal models, including diabetic mice and rabbits, ex vivo human skins, and Staphylococcus aureus-infected diabetic mice. In-depth mechanism investigation indicates that improved wound microenvironments accelerated wound repair, including alleviated bacterial infection, lessened inflammation, appearance of abundant M2-type macrophages, removal of ROS, promoted angiogenesis, and re-epithelialization. Collectively, our investigation provides an in situ, convenient, and effective approach for diabetic wound repair.

Protein-based bioactive coatings: from nanoarchitectonics to applications

Protein-based bioactive coatings have emerged as a versatile and promising strategy for enhancing the performance and biocompatibility of diverse biomedical materials and devices. Through surface modification, these coatings confer novel biofunctional attributes, rendering the material highly bioactive. Their widespread adoption across various domains in recent years underscores their importance. This review systematically elucidates the behavior of protein-based bioactive coatings in organisms and expounds on their underlying mechanisms. Furthermore, it highlights notable advancements in artificial synthesis methodologies and their functional applications in vitro. A focal point is the delineation of assembly strategies employed in crafting protein-based bioactive coatings, which provides a guide for their expansion and sustained implementation. Finally, the current trends, challenges, and future directions of protein-based bioactive coatings are discussed.

Synthesis and functionalization of scalable and versatile 2D protein films via amyloid-like aggregation

Two-dimensional (2D) protein films can be used to modify the properties of surfaces, and find applications predominantly in the fields of biomaterials, lithography, optics and electronics. However, it is difficult to produce scalable homogeneous and robust protein films with an easy, low-cost, green and efficient method. Further challenges include encapsulating and releasing functional building blocks in the film without inactivating them, and maintaining or improving the bioactivities of proteins used for the formation of the films. Here we detail the process to prepare large 2D protein films with user-defined features and structures via the amyloid-like aggregation of commonly synthesized proteins. These films can be synthesized at meter scales, have high interface adhesion, high functional expansibility and tunable functional properties, obtained by controlling the position of the disulfide bond breakage. For example, we can retain or even enhance the natural antibacterial, biomineralization and antifouling activity of proteins involved in film formation, and the properties can also be expanded through the physical blending or chemical grafting of additional functional blocks on the surface of the film. A 2D protein film can be prepared in ~3 h using four alternative coating techniques: immersion, transfer, hydrogel stamping and spraying. The characterization process of the film requires ~5 d. The procedure can be carried out by users with basic expertise in materials science.

Identification and Characterization of a Predominant Hydrophobin in the Edible Mushroom Grifola frondosa

Hydrophobins (HFBs) are a group of small, secreted amphipathic proteins of fungi with multiple physiological functions and potential commercial applications. In this study, HFB genes of the edible mushroom, Grifola frondosa, were systematically identified and characterized, and their transcriptional profiles during fungal development were determined. In total, 19 typical class I HFB genes were discovered and bioinformatically analyzed. Gene expression profile examination showed that Gf.hyd9954 was particularly highly upregulated during primordia formation, suggesting its major role as the predominant HFB in the lifecycle of G. frondosa. The wettability alteration profile and the surface modification ability of recombinant rGf.hyd9954 were greater than for the Grifola HFB HGFII-his. rGf.hyd9954 was also demonstrated to form the typical class I HFB characteristic-rodlet bundles. In addition, rGf.hyd9954 was shown to possess nanoparticle characteristics and emulsification activities. This research sheds light on the regulation of fungal development and its association with the expression of HFB genes.

Modification of Low-Energy Surfaces Using Bicyclic Peptides Discovered by Phage Display

Solid-binding peptides are a simple and versatile tool for the non-covalent modification of solid material surfaces, and a variety of peptides have been developed by reference to natural proteins or de novo design. Here, for the first time, we report the discovery of a bicyclic peptide targeting the heterogeneous material polypropylene by combining phage display technology and next-generation sequencing. We find that the enrichment properties of bicyclic peptides capable of binding to polypropylene are distinct from linear peptides, as reflected in amino acid abundance and a trend toward negative net charges and high hydrophobicity. The selected bicyclic peptide has a higher binding affinity for polypropylene compared with a previously reported linear peptide, enabling the hydrophilic and adhesive properties of the polypropylene to be more effectively enhanced. Our work paves the way for the exploration and utilization of conformational-restricted cyclic peptides as a new family of functionally evolvable agents for material surface modification.

Full-colour Jabuticaba-like nanostructures via the multiplex and orthogonal self-assembly of protein-conjugated quantum dots with engineered biofilms

The integration of inorganic components with bacterial biofilms is of great significance for expanding the functionality of artificial biological materials. However, so far, the complexities and functionalities of biofilm-based scaffolds assembled via metal-peptide coordination chemistries remain limited. Here, we present a platform for the multiplexed and specific coupling of recombinant protein-functionalized fluorescent red-green-blue (RGB) quantum dots (QDs) with engineered biofilms to form Jabuticaba-like nanostructures. Full-color living Jabuticaba-like nanostructures have been achieved through the interaction of extracellular peptides that are fabricated by biofilms with the proteins that modify the surface of the RGB QDs through orthogonal SpyTag/SpyCatcher, IsopeptagN/PilinN, and IsopeptagC/PilinC pairs. We envision that living cell populations will enable the multiplexable, scalable and bottom-up assembly of versatile materials that integrate both abiotic and biotic components into multifunctional systems.

Application of the neuropeptide NPVF to enhance angiogenesis and osteogenesis in bone regeneration

The brain-bone regulatory system regulates skeletal homeostasis via bioactive neuropeptides, yet the underlying mechanism remains elusive. Here, we report the role of the neuropeptide VF (NPVF, VPNLPQRF-NH2) in enhancing both angiogenesis and osteogenesis in a rat skeletal system and the potential pathways involved. An in vitro study revealed that NPVF not only promotes migration and angiogenesis of human umbilical vein endothelial cells (HUVECs) by activating NPFFR1, which leads to upregulation of miR-181c-3p and downregulation of Argonaute1 (AGO1), but also mediates osteogenic differentiation of bone mesenchymal stem cells (BMSCs) via the Wnt/β-catenin signaling pathway. To improve the stability and bioavailability and thus efficacy of NPVF as a promoter of in vivo bone regeneration, we genetically engineered amyloid-NPVF-fusion proteins and utilized them as self-assembling nanofiber coatings to treat bone defects in a rat calvarial defect model. We found that a porous hydroxyapatite scaffold loaded with the NPVF peptide-fused amyloid coating substantially enhanced angiogenesis and site-specific fresh bone in-growth when implanted in calvarial defects. Taken together, our work uncovered a previously undefined crosstalk between the brain and bone by unveiling the role of NPVF in bone tissue and demonstrated a viable method for promoting bone tissue repairs based upon self-assembling NPVF-containing protein coatings.

Biopolymer coating for particle surface engineering and their biomedical applications

Surface engineering of particles based on a polymeric coating is of great interest in materials design and applications. Due to the disadvantages of non-biodegradability and undesirable biocompatibility, the application of petroleum-based synthetic polymers coating in the biomedical field has been greatly limited. In addition, there is lack of a universal surface modification method to functionalize particles of different compositions, sizes, shapes, and structures. Thus, it is imperative to develop a versatile biopolymeric coating with good biocompatibility and tunable biodegradability for the preparation of functional particle materials regardless of their surface chemical and physical structures. Recently, the natural polysaccharide polymers (e.g. chitosan and cellulose), polyphenol-based biopolymers (e.g. polydopamine and tannic acid), and proteins (e.g. amyloid-like aggregates) have been utilized in surface modification of particles, and applications of these modified particles in the field of biomedicine have been also intensively exploited. In this review, the preparation of the above three coatings on particles surface are summarized, and the applications of these materials in drug loading/release, biomineralization, cell immobilization/protection, enzyme immobilization/protection, and antibacterial/antiviral are exemplified. Finally, the challenges and the future research directions on biopolymer coating for particles surface engineering are prospected.

Rational Design of a Zr-MOF@Curli-Polyelectrolyte Hybrid Membrane toward Efficient Chemical Protection, Moisture Permeation, and Catalytic Detoxification

Developing high-performance protective materials is important for soldiers and civilians who are exposed to the atmosphere of highly toxic chemical warfare agents (CWAs). Polyelectrolyte membranes are promising candidates with excellent chemical resistance and moisture permeability, but they cannot efficiently degrade CWAs. Here, we design and prepare a hybrid membrane through in situ growth of catalytically active zirconium-based metal-organic frameworks (Zr-MOFs) on a polyelectrolyte membrane mediated by biofilm-inspired curli nanofibers (CNFs). Superior to the bare polyelectrolyte membrane, the prepared MOF-808@CNF-PQ hybrid membrane exhibits improved rejection of the nerve agent simulant dimethyl methyl phosphonate (DMMP) vapor and permeation of the water vapor by 113 and 45%, respectively. The water/DMMP selectivity of the hybrid membrane reaches 498.6, approximately 13 times that of the commercial polyelectrolyte membrane Nafion 117. In addition, the hybrid membrane possesses appreciable catalytic activity for the hydrolysis of the nerve agent simulant dimethyl 4-nitrophenyl phosphate (DMNP) with a half-life of ∼38 min. Nanomechanical characterization results based on atomic force microscopy (AFM) techniques demonstrate the critical role of CNFs in mediating Zr-MOF nucleation and the dominant effect of electrostatic interactions on self-assembly of CNFs on polyelectrolyte base. It is also confirmed that the Zr-MOF toppings serve as the key components in physically adsorbing and chemically degrading the DMNP molecules through multiple strong intermolecular interactions. Our work offers a rational strategy to develop advanced membranes toward efficient chemical protection, moisture permeation, and catalytic detoxification against CWAs.

Molecular-level insights into the surface-induced assembly of functional bacterial amyloid

Protein coating material is important in many technological fields. The interaction between carbon nanomaterial and protein is especially interesting since it makes the development of novel hybrid materials possible. Functional bacterial amyloid (FuBA) is promising as a coating material because of its desirable features, such as well-defined molecular structure, robustness against harsh conditions, and easily engineerable functionality. Here, we report the systematic assembly of the functional amyloid protein, CsgA, from Escherichia coli (E. coli) on graphite. We characterize the assemblies using scanning tunneling microscopy (STM) and show that CsgA forms assemblies according to systematic patterns, dictated by the graphite lattice. In addition, we show that graphite flakes induce the fibrillization of CsgA, in vitro, suggesting a surface-induced conformational change of CsgA facilitated by the graphite lattice. Using coarse-grained molecular dynamics simulations, we model the adhesion and lamellar formation of a CsgA-derived peptide and conclude that peptides are adsorbed both as monomers and smaller aggregates leading initially to unordered graphite-bound aggregates, which are followed by rearrangement into lamellar structures. Finally, we show that CsgA-derived peptides can be immobilized in very systematic assemblies and their molecular orientation can be tuned using a small chaperone-like molecule. Our findings have implications for the development of FuBA-based biosensors, catalysts, and other technologies requiring well-defined protein assemblies on graphite.

Application of Porous Polyetheretherketone Scaffold/ Vancomycin-Loaded Thermosensitive Hydrogel Composites for Antibacterial Therapy in Bone Repair

Polyetheretherketone (PEEK) has been widely used in bone repair, but it often fails due to bacterial infection. Herein, a high-strength porous polyetheretherketone scaffold (ps-PK) loaded with antibacterial drug-loaded hydrogel strategy is proposed. The prepared ps-PK possesses high porosity (30.8%-64.7%) and the compression modulus is between 0.4-0.98 GPa. The interconnected pore-type structure endows it with a drug loading capacity. Poly(_D,L -lactic acid-co-glycolic acid)-b-Poly(ethylene glycol)-b-Poly(_D,L -lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) thermoresponsive hydrogels loaded with vancomycin are used as the drug sustained-release system. The vancomycin-loaded hydrogels in the solution state at a low temperature were filled into a porous polyetheretherketone scaffold (ps-PK-VGel) and formed a gel state after implantation in vivo. The antibacterial rate of ps-PK-VGel against methicillin-resistant staphylococcus aureus (MRSA) in vitro was 99.7% and histological observation in vivo demonstrates that the ps-PK-VGel shows obvious antibacterial activity. Given its excellent antibacterial ability and mechanical properties, the porous PEEK scaffold composite drug-loaded thermosensitive hydrogel has great potential in bone repair surgery applications. This article is protected by copyright. All rights reserved.

Engineered Living Hydrogels

Living biological systems, ranging from single cells to whole organisms, can sense, process information, and actuate in response to changing environmental conditions. Inspired by living biological systems, engineered living cells and nonliving matrices are brought together, which gives rise to the technology of engineered living materials. By designing the functionalities of living cells and the structures of nonliving matrices, engineered living materials can be created to detect variability in the surrounding environment and to adjust their functions accordingly, thereby enabling applications in health monitoring, disease treatment, and environmental remediation. Hydrogels, a class of soft, wet, and biocompatible materials, have been widely used as matrices for engineered living cells, leading to the nascent field of engineered living hydrogels. Here, the interactions between hydrogel matrices and engineered living cells are described, focusing on how hydrogels influence cell behaviors and how cells affect hydrogel properties. The interactions between engineered living hydrogels and their environments, and how these interactions enable versatile applications, are also discussed. Finally, current challenges facing the field of engineered living hydrogels for their applications in clinical and environmental settings are highlighted.

Functional Bacterial Amyloids: Understanding Fibrillation, Regulating Biofilm Fibril Formation and Organizing Surface Assemblies

Functional amyloid is produced by many organisms but is particularly well understood in bacteria, where proteins such as CsgA (E. coli) and FapC (Pseudomonas) are assembled as functional bacterial amyloid (FuBA) on the cell surface in a carefully optimized process. Besides a host of helper proteins, FuBA formation is aided by multiple imperfect repeats which stabilize amyloid and streamline the aggregation mechanism to a fast-track assembly dominated by primary nucleation. These repeats, which are found in variable numbers in Pseudomonas, are most likely the structural core of the fibrils, though we still lack experimental data to determine whether the repeats give rise to β-helix structures via stacked β-hairpins (highly likely for CsgA) or more complicated arrangements (possibly the case for FapC). The response of FuBA fibrillation to denaturants suggests that nucleation and elongation involve equal amounts of folding, but protein chaperones preferentially target nucleation for effective inhibition. Smart peptides can be designed based on these imperfect repeats and modified with various flanking sequences to divert aggregation to less stable structures, leading to a reduction in biofilm formation. Small molecules such as EGCG can also divert FuBA to less organized structures, such as partially-folded oligomeric species, with the same detrimental effect on biofilm. Finally, the strong tendency of FuBA to self-assemble can lead to the formation of very regular two-dimensional amyloid films on structured surfaces such as graphite, which strongly implies future use in biosensors or other nanobiomaterials. In summary, the properties of functional amyloid are a much-needed corrective to the unfortunate association of amyloid with neurodegenerative disease and a testimony to nature's ability to get the best out of a protein fold.

Assessment of Neurodegenerative Changes in Turkeys Fed Diets with Different Proportions of Arginine and Methionine Relative to Lysine

Simple Summary

It is important to take care of a properly balanced amino acid composition in the diet in order to inhibit or delay the occurrence of processes and changes related to the destruction of nervous tissue. Therefore, an attempt was made in this manuscript to evaluate the effect of different ratios of the key amino acids arginine and methionine, relative to lysine, in relation to two turkey feeding standards. The amino acid guidelines formulated by British United Turkeys (BUT) suggest higher levels of lysine (Lys) in turkey diets than those recommended by the National Research Council (NRC). In order to assess the impact of such supplementation, we analyzed the level of indicators informing the presence or degree of advancement of neurodegenerative processes in the nervous tissue (the level of acetylcholinesterase and amyloid-β; the concentration of AChE complexes with amyloid-β and Tau protein, called glycosylated acetylcholinesterase (GAChE), indicative of the destruction of neurons). The level of low-density lipoprotein receptor-related protein 1, or LRP-1, which facilitates the breakdown of toxic amyloid-β, was also assessed. In addition, the effect of different doses of these amino acids on neurodegenerative changes in DNA, especially the degree of methylation of histone proteins resulting from covalent modifications was compared between lysine and arginine residues.

Abstract

We postulated that the use of optimal levels and proportions of Arg and Met relative to a low or high concentration of Lys in diets for meat turkeys would reduce the occurrence of metabolic disturbances in the nervous tissue that can lead to neurodegenerative changes. The aim of the study was to determine the effect of various proportions of Lys, Arg, and Met in diets for turkeys, with a low content of Lys in accordance with NRC (Experiment 1) recommendations, and in diets with high Lys levels that are close to the recommendations of breeding companies (Experiment 2) on selected indicators of potential neurodegenerative effects in the brain and liver of turkeys. The Experiment 1 and Experiment 2 was conducted using 864 day-old turkey chicks randomly assigned to six groups, in eight replicates (6 groups × 18 birds × 8 replicates). A full description of the methodology can be found in previously published papers using the same experimental design. Indicators informing about the presence or advancement of neurodegenerative processes in the nervous tissue were determined in the brain and liver (level of: AChE, amyloid-β, GAChE, Tau protein, LRP1, and the degree of DNA methylation). It was established that in the case of both a low (National Research Council, NRC) and a high (British United Turkeys, BUT) level of Lys in the diet of turkeys, the Arg level can be reduced to 90% of the Lys level and Met to 30% of the Lys level, because this does not cause neurodegenerative changes in turkeys. Unfavorable neurodegenerative changes may appear if the Arg level is increased from 100 to 110% of the Lys level recommended by the NRC. However, due to the lack of such a relationship when Arg is increased from 100 to 110% of the Lys level recommended by BUT, at this stage of research no definitive conclusions can be drawn regarding the risk of neurodegenerative changes caused by increasing Arg in the diet of turkeys.

Encoding with a fluorescence-activating and absorption-shifting tag generates living bacterial probes for mammalian microbiota imaging

The mammalian microbiota plays essential roles in health. A primary determinant to understand the interaction with the host is the distribution and viability of its key microorganisms. Here, a strategy of encoding with a fluorescence-activating and absorption-shifting tag (FAST) is reported to prepare living bacterial probes for real-time dynamic, dual-modal, and molecular oxygen-independent imaging of the host microbiota. Carrying FAST endows bacteria with rapid on-demand turn on-off fluorescence by adding or removal of corresponding fluorogens. Encoded bacteria are able to reversibly switch emission bands for dual-color fluorescence imaging via fluorogen exchange. Due to molecular oxygen-independent emission of FAST, encoded bacteria can emit fluorescence under anaerobic environments including the gut and tumor. These living probes demonstrate the applicability to quantify the vitality of bacteria transplanted to the gut microbiota. This work proposes a unique fluorescence probe for investigating the dynamics of the host microbiota.

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Living bacterial probes for real-time dynamic, dual-modal, and molecular oxygen-independent imaging of mammalian microbiota.

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Engineered bacteria showing on-demand turn on-off fluorescence by adding or removal of corresponding fluorogens.

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Fluorescence emission under anaerobic in vivo environments including the gut and tumor.

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A fluorescence probe to determine the vitality of transplanted bacteria and investigate the dynamics of the host microbiota.

Protein Mediated Enzyme Immobilization

Enzyme immobilization is an essential technology for commercializing biocatalysis. It imparts stability, recoverability, and other valuable features that improve the effectiveness of biocatalysts. While many avenues to join an enzyme to solid phases exist, protein-mediated immobilization is rapidly developing and has many advantages. Protein-mediated immobilization allows for the binding interaction to be genetically coded, can be used to create artificial multienzyme cascades, and enables modular designs that expand the variety of enzymes immobilized. By designing around binding interactions between protein domains, they can be integrated into functional materials for protein immobilization. These materials are framed within the context of biocatalytic performance, immobilization efficiency, and stability of the materials. In this review, supports composed entirely of protein are discussed first, with systems such as cellulosomes and protein cages being discussed alongside newer technologies like spore-based biocatalysts and forizymes. Protein-composite materials such as polymersomes and protein-inorganic supraparticles are then discussed to demonstrate how protein-mediated strategies are applied to many classes of solid materials. Critical analysis and future directions of protein-based immobilization are then discussed, with a particular focus on both computational and design strategies to advance this area of research and make it more broadly applicable to many classes of enzymes.

Amyloid-Templated Palladium Nanoparticles for Water Purification by Electroreduction

Electrocatalysis offers great promise for water purification but is limited by low active area and high uncontrollability of electrocatalysts. To overcome these constraints, we propose hybrid bulk electrodes by synthesizing and binding a Pd nanocatalyst (nano-Pd) to the electrodes via amyloid fibrils (AFs). The AFs template is effective for controlling the nucleation, growth, and assembly of nano-Pd on the electrode. In addition, the three-dimensional hierarchically porous nanostructure of AFs is beneficial for loading high-density nano-Pd with a large active area. The novel hybrid cathodes exhibit superior electroreduction performance for the detoxification of hexavalent chromium (Cr6+ ), 4-chlorophenol, and trichloroacetic acid in wastewater and drinking water. This study provides a proof-of-concept design of an AFs-templated nano-Pd-based hybrid electrode, which constitutes a paradigm shift in electrocatalytic water purification, and broadens the horizon of its potential engineered applications.

Oat Plant Amyloids for Sustainable Functional Materials

Amyloid functional materials from amyloid fibril building blocks, produced in vitro from amyloidogenic natural proteins or synthetic peptides, show diverse functionalities ranging from environmental science and biomedicine, to nanotechnology and biomaterials. However, sustainable and affordable sources of amyloidogenic proteins remain the bottleneck for large-scale applications, and to date, interest remains essentially limited to fundamental studies. Plant-derived proteins would be an ideal source due to their natural abundance and low environmental impact. Hereby oat globulin, the primary protein of oat plant (Avena sativa), is utilized to yield high-quality amyloid fibrils and functional materials based thereof. These fibrils show a rich multistranded ribbon-like polymorphism and a fibrillization process with both irreversible and reversible pathways. The authors furthermore fabricate oat-amyloid aerogels, films, and membranes for possible use in water purification, sensors, and patterned electrodes. The sustainability footprint of oat-amyloids against other protein sources is demonstrated, anticipating an environmentally-efficient platform for advanced materials and technologies.

Tag-mediated single-step purification and immobilization of recombinant proteins toward protein-engineered advanced materials

Background

The potential applications of protein-engineered functional materials are so wide and exciting that the interest in these eco-friendly advanced materials will further expand in the future. Tag-mediated protein purification/immobilization technologies have emerged as green and cost-effective approaches for the fabrication of such materials. Strategies that combine the purification and immobilization of recombinant proteins/peptides onto/into natural, synthetic or hybrid materials in a single-step are arising and attracting increasing interest.

Aim of Review

This review highlights the most significant advances of the last 5 years within the scope of tag-mediated protein purification/immobilization and elucidates their contributions for the development of efficient single-step purification and immobilization strategies. Recent progresses in the field of protein-engineered materials created using innovative protein-tag combinations and future opportunities created by these new technologies are also summarized and identified herein.

Key Scientific Concepts of Review

Protein purification/immobilization tags present a remarkable ability to establish specific non-covalent/covalent interactions between solid materials and biological elements, which prompted the creation of tailor-made and advanced functional materials, and of next-generation hybrid materials. Affinity tags can bind to a wide range of materials (of synthetic, natural or hybrid nature), being most suitable for protein purification. Covalently binding tags are most suitable for long-term protein immobilization, but can only bind naturally to protein-based materials. Hybrid affinity-covalently binding tags have allowed efficient one-step purification and immobilization of proteins onto different materials, as well as the development of innovative protein-engineered materials. Self-aggregating tags have been particularly useful in combination with other tags for generating protein-engineered materials with self-assembling, flexible and/or responsive properties. While these tags have been mainly explored for independent protein purification, immobilization or functionalization purposes, efficient strategies that combine tag-mediated purification and immobilization/functionalization in a single-step will be essential to guarantee the sustainable manufacturing of advanced protein-engineered materials.

Functional amyloid-chitin hybrid ink coupled with flexible fabrication approaches for diverse macro and micro-structures

The precise fabrication of artificially designed molecular complexes into ordered structures resembling their natural counterparts would find broad applications but remains a major challenge in the field. Here we genetically design chitin-binding domain (CBD)-containing amyloid proteins, and rationally fabricate well-ordered CBD-containing functional amyloid-chitin complex structures by coupling a top-down manufacturing process with a bottom-up self-assembly. Our fabrication approach starts with the dissolution of both CBD-containing functional amyloid and chitin in hexafluoroisopropanol (HFIP) to make a hybrid ink. This hybrid ink platform, coupled with multiple fabrication methods including airbrushing, electrospinning and soft-lithography, produces a series of unique freestanding structures. The structural features of the products, such as the ability to direct the light path and mimicking of the extracellular matrix enable applications in functional light gratings and cell culture, respectively. Further genetic engineering of the protein component allowed tunable functionalization of these materials, including nanoparticle immobilization and protein conjugation, resulting in broad applications in electronic devices and enzyme immobilization. Our technological platform can drive new advances in biocatalysis, tissue engineering, biomedicine, photonics and electronics.

Biofilm-Mediated Immobilization of a Multienzyme Complex for Accelerating Inositol Production from Starch

Bacterial biofilm, as a natural and renewable material, is a promising architecture for enzyme immobilization. In this study, we have demonstrated the feasibility of an Escherichia coli biofilm to immobilize a self-assembly multienzyme complex by the covalent interaction between a peptide SpyTag and its protein partner SpyCatcher. The SpyTag-labeled biofilm is displayed on the surface of E. coli by overexpressing the recombinant CsgA-SpyTag, in which CsgA is capable of forming biofilms. This SpyTag bearing biofilm is used to bind with SpyCatcher bearing synthetic mini-scaffoldin, which also contains a carbohydrate-binding module 3 (CBM3), and four different cohesins from different microorganisms. CBM3 was used to bind with cellulose, while the four different cohesins were used to recruit four dockerin-containing cascade enzymes, which were subsequently applied to convert starch to myo-inositol. Compared to the free enzyme mixture, the biofilm-immobilized enzyme complex exhibited a 4.28 times increase in initial reaction rate in producing myo-inositol from 10 g/L maltodextrin (a derivative of starch). Additionally, this biofilm-immobilized enzyme complex showed much higher recycle ability than the enzyme complex which was immobilized on a regenerated amorphous cellulose (RAC) system. In conclusion, the biofilm-mediated immobilization of the enzymatic biosystem provides a promising strategy to increase the reaction rate and enhance the stability of an in vitro enzymatic biosystem, exhibiting high potential to improve the efficiency of an in vitro biosystem.

Controlling the Structure and Function of Protein Thin Films through Amyloid-like Aggregation

Protein thin films (PTFs) with tunable structure and function can offer multiple opportunities in various fields such as surface modification, biomaterials, packaging, optics, electronics, separation, energy, and environmental science. Although nature may offer a variety of examples of high-level control of structure and function, e.g., the S layer of cells, synthetic alternatives for large-area protein-based thin films with fine control over both biological function and material structure are a key challenge, especially when aiming for facile, low-cost, green, and large-scale preparation as well as a further extension of function, such as the encapsulation and release of functional building blocks.Therefore, regarding the structure and function of PTFs, we will first briefly comment on the problems associated with PTF fabrication, and then, regarding the basis of our long-term research on protein-based thin films, we will summarize the new strategies that we have developed in recent years to explore and control the structure and function of PTFs for frontier research and practical applications.Inspired by naturally occurring protein amyloid fibrillization, we proposed the amyloid-like protein aggregation strategy to assemble proteins into supramolecular 2D films with extremely large sizes and enduring interfacial adhesion stability. This approach opened a new window for PTF fabrication in which the spontaneous interfacial 2D aggregation of protein oligomers instead of traditional 1D protofibril elongation directs the assembly of proteins. As a result, the film morphology, thickness, porosity, and function can be tailored by simply tuning the interfacial aggregation pathways.We further modified amyloid-like protein aggregation to develop chemoselective reaction-induced protein aggregation (CRIPA). It is well known that chemoselective reactions have been employed for protein modification. However, the application of such reactions in PTF fabrication has been overlooked. We initiated this new strategy by employing thiol-disulfide exchange reactions. These reactions are chemoselective toward proteins containing specific disulfide bonds with high redox potentials, resulting in amyloid-like aggregation and thin film formation. Functional proteins with immunity to such reactions can be encapsulated in thin films and released on demand without a loss of activity, opening a new avenue for the development of functional PTFs and coatings.Finally, the resultant amyloid-inspired PTFs, as a new type of biomimetic materials, provide a good platform for integration with various biomedical functions. Here, the creation of bioactive surfaces on virtually arbitrary substrates by amyloid-like PTFs will be discussed, highlighting antimicrobial, antifouling, molecular separation, and interfacial biomineralization activities that exceed those of their native protein precursors and synthetic alternatives.

Necessity of regulatory guidelines for the development of amyloid based biomaterials

Amyloid diseases are caused due to protein homeostasis failure where incorrectly folded proteins/peptides form cross-β-sheet rich amyloid fibrillar structures. Besides proteins/peptides, small metabolite assemblies also exhibit amyloid-like features. These structures are linked to several human and animal diseases. In addition, non-toxic amyloids with diverse physiological roles are characterized as a new functional class. This finding, along with the unique properties of amyloid like stability and mechanical strength, led to a surge in the development of amyloid-based biomaterials. However, the usage of these materials by humans and animals may pose a health risk such as the development of amyloid diseases and toxicity. This is possible because amyloid-based biomaterials and their fragments may assist seeding and cross-seeding mechanisms of amyloid formation in the body. This review summarizes the potential uses of amyloids as biomaterials, the concerns regarding their usage, and a prescribed workflow to initiate a regulatory approach.

Hybrid Living Capsules Autonomously Produced by Engineered Bacteria

Bacterial cellulose (BC) has excellent material properties and can be produced sustainably through simple bacterial culture, but BC-producing bacteria lack the extensive genetic toolkits of model organisms such as Escherichia coli (E. coli). Here, a simple approach is reported for producing highly programmable BC materials through incorporation of engineered E. coli. The acetic acid bacterium Gluconacetobacter hansenii is cocultured with engineered E. coli in droplets of glucose-rich media to produce robust cellulose capsules, which are then colonized by the E. coli upon transfer to selective lysogeny broth media. It is shown that the encapsulated E. coli can produce engineered protein nanofibers within the cellulose matrix, yielding hybrid capsules capable of sequestering specific biomolecules from the environment and enzymatic catalysis. Furthermore, capsules are produced which can alter their own bulk physical properties through enzyme-induced biomineralization. This novel system uses a simple fabrication process, based on the autonomous activity of two bacteria, to significantly expand the functionality of BC-based living materials.

Fabrication of fluorescent pH-responsive protein-textile composites

Wearable pH sensors are useful tools in the healthcare and fitness industries, allowing consumers to access information related to their health in a convenient manner via the monitoring of body fluids. In this work, we tailored novel protein-textile composites to fluorescently respond to changing pH. To do so, we used amyloid curli fibers, a key component in the extracellular matrix of Escherichia coli, as genetic scaffold to fuse a pH-responsive fluorescent protein, pHuji. Engineered amyloids form macroscopic and environmentally resistant aggregates that we isolated to use as stand-alone hydrogel-based sensors, and that we trapped within textile matrices to create responsive bio-composites. We showed that these composites were mechanically robust and vapor-permeable, thus exhibiting favorable characteristics for wearable platforms. CsgA-pHuji fibers integrated in the textile allowed the final device to respond to pH changes and distinguish between alkaline and acidic solutions. We demonstrated that the resulting composites could sustain their fluorescence response over days, and that their sensing ability was reversible for at least 10 high/low pH cycles, highlighting their potential for continuous monitoring. Overall, we introduced a biosynthesized amyloid-based textile composite that could be used as biosensing patch for a variety of applications in the smart textile industry.