Preparation of Well-Defined Fluorescent Nanoplastic Particles by Confined Impinging Jet Mixing

Research on the origin, distribution, detection, identification, and quantification of polymer nanoparticles (NPs) in the environment and their possible impact on animal and human health is surging. For different types of studies in this field, well-defined reference materials or mimics are needed. While isolated reports on the preparation of such materials are available, a simple and broadly applicable method that allows for the production of different NP types with well-defined, tailorable characteristics is still missing. Here, we demonstrate that a confined impinging jet mixing process can be used to prepare colloidally stable NPs based on polystyrene, polyethylene, polypropylene, and poly(ethylene terephthalate) with diameters below < 100 nm. Different fluorophores were incorporated into the NPs, to allow their detection in complex environments. To demonstrate their utility and detectability, fluorescent NPs were exposed to J774A.1 macrophages and visualized using laser scanning microscopy. Furthermore, we modified the NPs in a postfabrication process and changed their shape from spherical to heterogeneous geometries, in order to mimic environmentally relevant morphologies. The methodology used here should be readily applicable to other polymers and payloads and thus a broad range of NPs that enable studies of their behavior, uptake, translocation, and biological end points in different systems.

Nanoscale clustering by O-antigen-Secretory Immunoglobulin-A binding limits outer membrane diffusion by encaging individual Salmonella cells

Secreted immunoglobulins, predominantly SIgA, influence the colonization and pathogenicity of mucosal bacteria. While part of this effect can be explained by SIgA-mediated bacterial aggregation, we have an incomplete picture of how SIgA binding influences cells independently of aggregation. Here we show that akin to microscale crosslinking of cells, SIgA targeting the Salmonella Typhimurium O-antigen extensively crosslinks the O-antigens on the surface of individual bacterial cells at the nanoscale. This crosslinking results in an essentially immobilized bacterial outer membrane. Membrane immobilization, combined with Bam-complex mediated outer membrane protein insertion results in biased inheritance of IgA-bound O-antigen, concentrating SIgA-bound O-antigen at the oldest poles during cell growth. By combining empirical measurements and simulations, we show that this SIgA-driven biased inheritance increases the rate at which phase-varied daughter cells become IgA-free: a process that can accelerate IgA escape via phase-variation of O-antigen structure. Our results show that O-antigen-crosslinking by SIgA impacts workings of the bacterial outer membrane, helping to mechanistically explain how SIgA may exert aggregation-independent effects on individual microbes colonizing the mucosae.

Global survival trends for brain tumors, by histology: analysis of individual records for 556,237 adults diagnosed in 59 countries during 2000-2014 (CONCORD-3)

BACKGROUND

Survival is a key metric of the effectiveness of a health system in managing cancer. We set out to provide a comprehensive examination of worldwide variation and trends in survival from brain tumors in adults, by histology.

METHODS

We analyzed individual data for adults (15-99 years) diagnosed with a brain tumor (ICD-O-3 topography code C71) during 2000-2014, regardless of tumor behavior. Data underwent a 3-phase quality control as part of CONCORD-3. We estimated net survival for 11 histology groups, using the unbiased nonparametric Pohar Perme estimator.

RESULTS

The study included 556,237 adults. In 2010-2014, the global range in age-standardized 5-year net survival for the most common sub-types was broad: in the range 20%-38% for diffuse and anaplastic astrocytoma, from 4% to 17% for glioblastoma, and between 32% and 69% for oligodendroglioma. For patients with glioblastoma, the largest gains in survival occurred between 2000-2004 and 2005-2009. These improvements were more noticeable among adults diagnosed aged 40-70 years than among younger adults.

CONCLUSIONS

To the best of our knowledge, this study provides the largest account to date of global trends in population-based survival for brain tumors by histology in adults. We have highlighted remarkable gains in 5-year survival from glioblastoma since 2005, providing large-scale empirical evidence on the uptake of chemoradiation at population level. Worldwide, survival improvements have been extensive, but some countries still lag behind. Our findings may help clinicians involved in national and international tumor pathway boards to promote initiatives aimed at more extensive implementation of clinical guidelines.

Bactericidal and Antiviral Bionic Metalized Nanocoatings

In diverse living organisms, bionanocoatings provide multiple functionalities, to the surfaces they cover. We have, previously, identified the molecular mechanisms of Turing-based self-assembly of insect corneal nanocoatings and developed forward-engineering approaches to construct multifunctional soft bionic nanocoatings, encompassing the Drosophila protein Retinin. Here, we expand the versatility of the bionic nanocoatings, by identifying and using diverse Retinin-like proteins and different methods of their metallization, using nickel, silver, and copper ions. Comparative assessment, of the resulting bactericidal, antiviral, and cytotoxic properties, identifies the best protocols, to construct safe and anti-infective metalized bionic nanocoatings. Upscaled application of these protocols, to various public surfaces, may represent a safe and economic approach to limit hazardous infections.

Liquid Crystalline Properties of Symmetric and Asymmetric End-Grafted Cellulose Nanocrystals

The hydrophilic polymer poly[2-(2-(2-methoxy ethoxy)ethoxy)ethylacrylate] (POEG₃A) was grafted onto the reducing end-groups (REGs) of cellulose nanocrystal (CNC) allomorphs, and their liquid crystalline properties were investigated. The REGs on CNCs extracted from cellulose I (CNC-I) are exclusively located at one end of the crystallite, whereas CNCs extracted from cellulose II (CNC-II) feature REGs at both ends of the crystallite, so that grafting from the REGs affords asymmetrically and symmetrically decorated CNCs, respectively. To confirm the REG modification, several complementary analytical techniques were applied. The grafting of POEG₃A onto the CNC REGs was evidenced by Fourier transform infrared spectroscopy, atomic force microscopy, and the coil-globule conformational transition of this polymer above 60 °C, i.e., its lower critical solution temperature. Furthermore, we investigated the self-assembly of end-tethered CNC-hybrids into chiral nematic liquid crystalline phases. Above a critical concentration, both end-grafted CNC allomorphs form chiral nematic tactoids. The introduction of POEG₃A to CNC-I does not disturb the surface of the CNCs along the rods, allowing the modified CNCs to approach each other and form helicoidal textures. End-grafted CNC-II formed chiral nematic tactoids with a pitch observable by polarized optical microscopy. This is likely due to their increase in hydrodynamic radius or the introduced steric stabilization of the end-grafted polymer.

Different Folding States from the Same Protein Sequence Determine Reversible vs Irreversible Amyloid Fate

The propensity to self-assemble into amyloid fibrils with a shared cross-β architecture is a generic feature of proteins. Amyloid-related diseases affect millions of people worldwide, yet they are incurable and cannot be effectively prevented, largely due to the irreversible assembly and extraordinary stability of amyloid fibrils. Recent studies suggest that labile amyloids may be possible in certain proteins containing low-complexity domains often involved in the formation of subcellular membraneless organelles. Although the fundamental understanding of this reversible amyloid folding process is completely missing, the current view is that a given protein sequence will result in either irreversible, as in most of the cases, or reversible amyloid fibrils, as in few exceptions. Here we show that two common globular proteins, human lysozyme and its homologue from hen egg white, can self-assemble into both reversible and irreversible amyloid fibrils depending on the folding path followed by the protein. In both folding states, the amyloid nature of the fibrils is demonstrated at the molecular level by its cross-β structure, yet with substantial differences on the mesoscopic polymorphism and the labile nature of the amyloid state. Structural analysis shows that reversible and irreversible amyloid fibrils possess the same full-length protein sequence but different fibril core structures and β-sheet arrangements. These results illuminate a mechanistic link between the reversible and irreversible nature of amyloids and highlight the central role of protein folding states in regulating the lability and reversibility of amyloids.

A rationally designed oral vaccine induces immunoglobulin A in the murine gut that directs the evolution of attenuated Salmonella variants

The ability of gut bacterial pathogens to escape immunity by antigenic variation-particularly via changes to surface-exposed antigens-is a major barrier to immune clearance¹. However, not all variants are equally fit in all environments^2,3. It should therefore be possible to exploit such immune escape mechanisms to direct an evolutionary trade-off. Here, we demonstrate this phenomenon using Salmonella enterica subspecies enterica serovar Typhimurium (S.Tm). A dominant surface antigen of S.Tm is its O-antigen: a long, repetitive glycan that can be rapidly varied by mutations in biosynthetic pathways or by phase variation^4,5. We quantified the selective advantage of O-antigen variants in the presence and absence of O-antigen-specific immunoglobulin A and identified a set of evolutionary trajectories allowing immune escape without an associated fitness cost in naive mice. Through the use of rationally designed oral vaccines, we induced immunoglobulin A responses blocking all of these trajectories. This selected for Salmonella mutants carrying deletions of the O-antigen polymerase gene wzyB. Due to their short O-antigen, these evolved mutants were more susceptible to environmental stressors (detergents or complement) and predation (bacteriophages) and were impaired in gut colonization and virulence in mice. Therefore, a rationally induced cocktail of intestinal antibodies can direct an evolutionary trade-off in S.Tm. This lays the foundations for the exploration of mucosal vaccines capable of setting evolutionary traps as a prophylactic strategy.

Engineering of biofilms with a glycosylation circuit for biomaterial applications

Glycosylation is a crucial post-translational modification for a wide range of functionalities. Adhesive protein-based biomaterials in nature rely on heavily glycosylated proteins such as spider silk and mussel adhesive proteins. Engineering protein-based biomaterials genetically enables desired functions and characteristics. Additionally, utilization of glycosylation for biomaterial engineering can expand possibilities by including saccharides to the inventory of building blocks. Here, de novo glycosylation of Bacillus subtilis amyloid-like biofilm protein TasA using a Campylobacter jejuni glycosylation circuit is proposed to be a novel biomaterial engineering method for increasing adhesiveness of TasA fibrils. A C. jejuni glycosylation motif is genetically incorporated to tasA gene and expressed in Escherichia coli containing the C. jejuni pgl protein glycosylation pathway. Glycosylated TasA fibrils indicate enhanced adsorption on the gold surface without disruption of fibril formation. Our findings suggest that N-linked glycosylation can be a promising tool for engineering protein-based biomaterials specifically regarding adhesion.

Understanding the Formation of Apoferritin Amyloid Fibrils

We present the optimization of experimental conditions to yield long, rigid apoferritin protein amyloid fibrils, as well as the corresponding fibrillation pathway. Fibril growth kinetics was followed using atomic force microscopy (AFM), transmission electron microscopy (TEM), dynamic light scattering (DLS), circular dichroism (CD), fourier-transform infrared spectroscopy (FTIR), and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Among the morphologies identified, we show that the conditions result in small aggregates, as well as medium and long fibrils. Extended incubation times led to progressive unfolding and hydrolysis of the proteins into very short peptide fragments. AFM, SDS-PAGE, and CD support a universal common fibrillation mechanism in which hydrolyzed fragments play the central role. These collective results provide convincing evidence that protein unfolding and complete hydrolysis of the proteins into very short peptide sequences are essential for the formation of the final apoferritin amyloid-like fibrils.

Evolution of Conformation, Nanomechanics, and Infrared Nanospectroscopy of Single Amyloid Fibrils Converting into Microcrystals

Nanomechanical properties of amyloid fibrils and nanocrystals depend on their secondary and quaternary structure, and the geometry of intermolecular hydrogen bonds. Advanced imaging methods based on atomic force microscopy (AFM) have unravelled the morphological and mechanical heterogeneity of amyloids, however a full understanding has been hampered by the limited resolution of conventional spectroscopic methods. Here, it is shown that single molecule nanomechanical mapping and infrared nanospectroscopy (AFM-IR) in combination with atomistic modelling enable unravelling at the single aggregate scale of the morphological, nanomechanical, chemical, and structural transition from amyloid fibrils to amyloid microcrystals in the hexapeptides, ILQINS, IFQINS, and TFQINS. Different morphologies have different Young's moduli, within 2-6 GPa, with amyloid fibrils exhibiting lower Young's moduli compared to amyloid microcrystals. The origins of this stiffening are unravelled and related to the increased content of intermolecular β-sheet and the increased lengthscale of cooperativity following the transition from twisted fibril to flat nanocrystal. Increased stiffness in Young's moduli is correlated with increased density of intermolecular hydrogen bonding and parallel β-sheet structure, which energetically stabilize crystals over the other polymorphs. These results offer additional evidence for the position of amyloid crystals in the minimum of the protein folding and aggregation landscape.

Human neuropeptide substance P self-assembles into semi-flexible nanotubes that can be manipulated for nanotechnology

Substance P neuropeptide is here reported to self-assemble into well-defined semi-flexible nanotubes. Using a blend of synchrotron small angle X-ray scattering, atomic force microscopy and other biophysical techniques, the natural peptide is shown to self-assemble into monodisperse 6 nm wide nanotubes, which can closely associate into nano-arrays with nematic properties. Using simple protocols, the nanotubes could be precipitated or mineralised while conserving their dimensions and core-shell morphology. Our discovery expands the small number of available monodisperse peptide nanotube systems for nanotechnology, beyond direct relevance to biologically functional peptide nanostructures since the substance P nanotubes are fundamentally different from typical amyloid fibrils.

Covalent β-lactoglobulin-maltodextrin amyloid fibril conjugate prepared by the Maillard reaction

The surface modification of β-lactoglobulin amyloid fibrils (AFs) was investigated by performing the Maillard reaction with the free anomeric carbon of the maltodextrin in water at pH 9.0 and 90 °C. The bonding of maltodextrin to fibrils was confirmed by determining the free amino group content and the presence of final products from the Maillard reaction. The secondary structure of AFs was preserved as observed by circular dichroism analysis. Atomic force microscopy evidenced that prolonged heat treatment caused hydrolysis of the attached polysaccharide and consequently lowered the height of the fibrils from 8.0 nm (after 1 h) to 6.0 nm (after 24 h), which led to the reduction of hydrophilicity of resulting conjugate. Increasing the reaction time, however, resulted in the improvement of colloidal stability and decrease in turbidity ascribed to the increment of glycation degree, as well as, a decrease in the isoelectric point of the protein-based supramolecular object.

Formation of Higher Structural Levels in λ-Carrageenan Induced by the Antimalarial Drug Chloroquine

The linear polysaccharide λ-carrageenan is the only one among the carrageenans not forming secondary, tertiary, and quaternary structures in the presence of inorganic ions. Chloroquine (CQ) is a well-established antimalaria drug also recently discussed in therapeutics against the COVID-19 pandemic. The interaction of this polysaccharide-ionic drug pair was investigated by combining UV-vis spectrophotometry and atomic force microscopy (AFM) imaging. A decrease of the UV peak assigned to free CQ and the occurrence of isosbestic points indicate the formation of complexes. High-resolution AFM height images revealed an increasing height of the single polysaccharide chains in the random coil state upon addition of CQ, indicating the formation of a secondary structure, followed by higher hierarchical aggregates. The disappearance of higher-ordered structures and the recovery of polysaccharide chains with primary structure were observed by introducing inorganic cations (Na⁺, K⁺, Ca²⁺), replacing the condensed CQ and paving the way to reversible ion-induced drug release.

Accelerated Amyloid Beta Pathogenesis by Bacterial Amyloid FapC

The gut-brain axis has attracted increasing attention in recent years, fueled by accumulating symptomatic, physiological, and pathological findings. In this study, the aggregation and toxicity of amyloid beta (Aβ), the pathogenic peptide associated with Alzheimer's disease (AD), seeded by FapC amyloid fragments (FapCS) of Pseudomonas aeruginosa that colonizes the gut microbiome through infections are examined. FapCS display favorable binding with Aβ and a catalytic capacity in seeding the peptide amyloidosis. Upon seeding, twisted Aβ fibrils assume a much-shortened periodicity approximating that of FapC fibrils, accompanied by a 37% sharp rise in the fibrillar diameter, compared with the control. The robust seeding capacity for Aβ by FapCS and the biofilm fragments derived from P. aeruginosa entail abnormal behavior pathology and immunohistology, as well as impaired cognitive function of zebrafish. Together, the data offer the first concrete evidence of structural integration and inheritance in peptide cross-seeding, a crucial knowledge gap in understanding the pathological correlations between different amyloid diseases. The catalytic role of infectious bacteria in promoting Aβ amyloidosis may be exploited as a potential therapeutic target, while the altered mesoscopic signatures of Aβ fibrils may serve as a prototype for molecular assembly and a biomarker for screening bacterial infections in AD.

Time-temperature-resolved functional and structural changes of phycocyanin extracted from Arthrospira platensis/Spirulina

Arthrospira platensis, commonly known as Spirulina, gains increasing importance as alternative protein source for food production and biotechnological systems. A promising area is functional high-value algae extracts, rich in phycocyanin, a protein-pigment complex derived from A. platensis. This complex has proven functionality as the only natural blue colorant, fluorescent marker and therapeutic agent. The structure-function relationship is heat sensitive, making thermal processing in its production and its subsequent application a crucial aspect. In continuous high-temperature short-time treatments, it was shown how a purified phycocyanin (mixture of allophycocyanin and c-phycocyanin) disassembled and denatured between 50 and 70 °C. Three characteristic transition temperatures were allocated to specific quaternary aggregates. In contrast to sequential chemical denaturation, phycocyanin's chromophore and protein structure were simultaneously affected by thermal processing. Through a functionality assessment, the findings help optimize the efficiency of raw material usage by defining a processing window, enabling targeted process control resulting in desired product properties.

Structure-property relationships of cellulose nanofibril hydro- and aerogels and their building blocks

As abundant and renewable materials with excellent mechanical and functional properties, cellulose nanomaterials are utilized in advanced structural, optical and electronic applications. However, in order to further improve and develop new cellulose nanomaterials, a better understanding of the interplay between the self-assembled materials and their building blocks is crucial. This paper describes the structure-property relationships between cellulose nanofibrils (CNFs) and their resulting self-assembled structures in the form of hydrogels and aerogels. Rheological experiments revealed that the transition from viscous to elastic state with the corresponding evolution of the properties of the CNF dispersion depends on the aspect ratio and can be described in terms of the dynamic overlap concentration. The elastic shear modulus was dependent on the aspect ratio at very low CNF concentrations, reaching a plateau, where only the concentration of CNFs was relevant. This transition point in shear modulus was exploited to determine the mesh size of the fibril network, which was found to be in excellent agreement with predictions from scaling arguments. These findings highlight the possibility to tune the self-assembled materials response directly from the bottom-up by the CNF particle structure and thus, suggest new assembly routes starting directly from the CNF design.

Metal ions confinement defines the architecture of G-quartet, G-quadruplex fibrils and their assembly into nematic tactoids

G-quadruplex, assembled from a square array of guanine (G) molecules, is an important structure with crucial biological roles in vivo but also a versatile template for ordered functional materials. Although the understanding of G-quadruplex structures is the focus of numerous studies, little is known regarding the control of G-quartet stacking modes and the spontaneous orientation of G-quadruplex fibrils. Here, the effects of different metal ions and their concentrations on stacking modes of G-quartets are elucidated. Monovalent cations (typically K+) facilitate the formation of G-quadruplex hydrogels with both heteropolar and homopolar stacking modes, showing weak mechanical strength. In contrast, divalent metal ions (Ca2+, Sr2+, and Ba2+) at given concentrations can control G-quartet stacking modes and increase the mechanical rigidity of the resulting hydrogels through ionic bridge effects between divalent ions and borate. We show that for Ca2+ and Ba2+ at suitable concentrations, the assembly of G-quadruplexes results in the establishment of a mesoscopic chirality of the fibrils with a regular left-handed twist. Finally, we report the discovery of nematic tactoids self-assembled from G-quadruplex fibrils characterized by homeotropic fibril alignment with respect to the interface. We use the Frank-Oseen elastic energy and the Rapini-Papoular anisotropic surface energy to rationalize two different configurations of the tactoids. These results deepen our understanding of G-quadruplex structures and G-quadruplex fibrils, paving the way for their use in self-assembly and biomaterials.

Rigid, Fibrillar Quaternary Structures Induced by Divalent Ions in a Carboxylated Linear Polysaccharide

Polysaccharides are ubiquitous in nature; they serve fundamental roles in vivo and are used for a multitude of food, pharmaceutical, cosmetic biomaterials, and biomedical applications. Here, the structure-property function for low acetylated Gellan gum hydrogels induced by divalent ions was established by means of optical, rheological, and microscopic techniques. The hydrogels interacted with visible light as revealed by birefringence and multiple scattering, as a consequence of quaternary, supramolecular fibrillar structures. The molecular assembly and structure were elucidated by statistical analysis and polymer physics concepts applied to high-resolution AFM height images and further supported by FTIR. This revealed intramolecular coil-to-single helix transitions, followed by lateral aggregation of single helices into rigid, fibrillar quaternary structures, ultimately responsible for gelation of the system. Calcium and magnesium chloride were shown to lead to fibrils up to heights of 6.0 nm and persistence lengths of several micrometers. The change in molecular structure affected the macroscopic gel stiffness, with the plateau shear modulus reaching ∼10⁵ Pa. These results shed light on the two-step gelation mechanism of linear polysaccharides, their conformational molecular changes at the single polymer level and ultimately the macroscale properties of the ensued gels.

Structure and dynamics of hagfish mucin in different saline environments

The defense mechanism of hagfish against predators is based on its ability to form slime within a few milliseconds. Hagfish slime consists of two main components, namely mucin-like glycoproteins and long protein threads, which together entrap vast amounts of water and thus form a highly dilute hydrogel. Here, we investigate the mucin part of this hydrogel, in particular the role of the saline marine environment on the viscoelasticity and structure. By means of dynamic light scattering (DLS), shear and extensional rheology we probe the diffusion dynamics, the flow behavior, and the longest filament breaking time of hagfish mucin solutions. Using DLS we find a concentration-independent diffusion coefficient - characteristic for polyelectrolytes - up to the entanglement regime of 0.2 mg ml-1, which is about ten times higher than the natural concentration of hagfish mucin in hagfish slime. We also observe a slow relaxation process associated with clustering, probably due to electrostatic interactions. Shear rheology further revealed that hagfish mucin possesses pronounced viscoelastic properties at high concentrations (3 mg ml-1), showing that mucin alone achieves mechanical properties similar to those of natural hagfish slime (mucins and protein threads). The main effects of added seawater salts, and predominantly CaCl2 is to reduce the intensity of the slow relaxation process, which suggests that calcium ions lead to an ionotropic gelation of hagfish mucins.

Stable Immobilization of Enzymes in a Macro- and Mesoporous Silica Monolith

Horseradish peroxidase isoenzyme C (HRP) and Engyodontium album proteinase K (proK) were immobilized inside macro- and mesoporous silica monoliths. Stable immobilization was achieved through simple noncovalent adsorption of conjugates, which were prepared from a polycationic, water-soluble second generation dendronized polymer (denpol) and the enzymes. Conjugates prepared from three denpols with the same type of repeating unit (r.u.), but different average lengths were compared. It was shown that there is no obvious advantage of using denpols with very long chains. Excellent results were achieved with denpols having on average 750 or 1000 r.u. The enzyme-loaded monoliths were tested as flow reactors. Comparison was made with microscopy glass coverslips onto which the conjugates were immobilized and with glass micropipettes containing adsorbed conjugates. High enzyme loading was achieved using the monoliths. Monoliths containing immobilized denpol-HRP conjugates exhibited good operational stability at 25 °C (for at least several hours), and good storage stability at 4 °C (at least for weeks) was demonstrated. Such HRP-containing monoliths were applied as continuous flow reactors for the quantitative determination of hydrogen peroxide in aqueous solution between 1 μM (34 ng/mL) and 50 μM (1.7 μg/mL). Although many methods for immobilizing enzymes on silica surfaces exist, there are only a few approaches with porous silica materials for the development of flow reactors. The work presented is a promising contribution to this field of research toward bioanalytical and biosynthetic applications.

Selective and Efficient Removal of Fluoride from Water: In Situ Engineered Amyloid Fibril/ZrO2 Hybrid Membranes

We report a new strategy for efficient removal of F^- from contaminated water streams, and it relies on carbon hybrid membranes made of amyloid fibril/ZrO₂ nanoparticles (<10 nm). These membranes exhibit superior selectivity for F^- against various competitive ions, with a distribution coefficient (K_d ) as high as 6820 mL g^-1 , exceeding commercial ion-exchange resins (IRA-900) by 180 times and outdoing the performance of most commercial carbon-activated aluminum membranes. At both low and high (ca. 200 mg L^-1 ) F^- concentrations, the membrane efficiency exceeds 99.5 % removal. For real untreated municipal tap water (ca. 2.8 mg L^-1 ) under continuous operating mode, data indicates that about 1750 kg water m^-2 membrane can be treated while maintaining drinking water quality, and the saturated membranes can be regenerated and reused several times without decrease in performance. This technology is promising for mitigating the problem of fluoride water contamination worldwide.

Primary, Secondary, Tertiary and Quaternary Structure Levels in Linear Polysaccharides: From Random Coil, to Single Helix to Supramolecular Assembly

Polysaccharides are ubiquitous in nature and represent an essential class of biopolymers with multiple levels of conformation and structural hierarchy. However, a standardized structural nomenclature, as in the case of proteins, is still lacking due to uncertainty on their hierarchical organization. In this work we use carrageenans as model polysaccharides to demonstrate that several structural levels exist and can be unambiguously resolved by statistical analysis on high resolution Atomic Force Microscopy images, supported by spectroscopic, X-ray scattering and rheological techniques. In direct analogy with proteins, we identify primary, secondary, tertiary and quaternary structures. The structure-property relationship induced by monovalent ions for κ-, ι- and the non-gelling control λ-carrageenan is established from the single chain regime to the occurrence of hydrogels at higher concentrations. For κ-carrageenan in the presence of potassium, a disorder-order transition from random coil to single helix is first observed (secondary structure), followed by intrachain supercoiling events (tertiary structure) and macroscopic anisotropic domains which are parts of a network (quaternary structure) with tunable elasticity up to ∼10³ Pa. In contrast, κ-carrageenan in the presence of sodium only produces changes in secondary structure without supercoiling events, prior to formation of gels, highlighting the ion-specificity of the process. Loosely intertwined single helices are observed for ι-carrageenan in the presence of sodium and potassium chloride, providing an elastic mesh with many junction zones, while λ-carrageenan does not undergo any structural change. A generality of the observed behavior may be inferred by extending these observations to a distinct class of polysaccharides, the weak carboxylic polyelectrolyte Gellan gum. These results advance our understanding of ion-specific structural changes of polysaccharides and the physical mechanisms responsible for their gelation.

Characterization of Efficiency and Mechanisms of Cold Atmospheric Pressure Plasma Decontamination of Seeds for Sprout Production

The consumption of fresh fruit and vegetable products has strongly increased during the past few decades. However, inherent to all minimally processed products is the short shelf life, and the risk of foodborne diseases, which have been increasingly related to such products in many parts of the world. Because of the favorable conditions for the growth of bacteria during the germination of seeds, sprouts are a frequent source for pathogenic bacteria, thus highlighting the need for seed decontamination to reduce the risk of foodborne illness. Consequently, this study focused on cold atmospheric pressure plasma (CAPP) treatment of artificially inoculated seeds in a diffuse coplanar surface barrier discharge to determine the inactivation efficiency for relevant foodborne pathogens and fungal spores. Plasma treatment of seeds resulted in a highly efficient reduction of microorganisms on the seed surface, while preserving the germination properties of seeds, at least for moderate treatment times. To characterize the mechanisms that contribute to microbial inactivation during plasma treatment, an experimental setup was developed to separate ultraviolet light (UV) and other plasma components. The combination of bacterial viability staining with confocal laser scanning microscopy was used to investigate the impact of ozone and other reactive species on the bacterial cells in comparison to UV. Further characterization of the effect of CAPP on bacterial cells by atomic force microscopy imaging of the same Escherichia coli cells before and after treatment revealed an increase in the surface roughness of treated E. coli cells and a decrease in the average height of the cells, which suggests physical damage to the cell envelope. In conclusion, CAPP shows potential for use as a decontamination technology in the production process of sprouts, which may contribute to food safety and prolonged shelf life of the product.

Adsorption and Interfacial Layer Structure of Unmodified Nanocrystalline Cellulose at Air/Water Interfaces

Nanocrystalline cellulose (NCC) is a promising biological nanoparticle for the stabilization of fluid interfaces.  However, the adsorption and interfacial layer structure of NCC are poorly understood as it is currently unknown how to form  NCC interfacial layers. Herein, we present parameters for the adsorption of unmodified NCC at the air-water (A/W) interface. Initial NCC adsorption is limited by diffusion, followed by monolayer saturation and decrease in surface tension at the time scale of hours. These results confirm the current hypothesis of a Pickering stabilization. NCC interfacial performance can be modulated by salt-induced charge screening, enhancing adsorption kinetics, surface load, and interfacial viscoelasticity. Adsorbed NCC layers were visualized by atomic force microscopy at planar Langmuir films and curved air bubbles, whereat NCC coverage was higher at curved interfaces. Structural analysis by neutron reflectometry revealed that NCC forms a discontinuous monolayer with crystallites oriented in the interfacial plane at a contact angle < 90°, favoring NCC desorption upon area compression. This provides the fundamental framework on the formation and structure of NCC layers at the A/W interface, paving the way for exploiting NCC interfacial stabilization for tailored colloidal materials.

Controlling Supramolecular Chiral Nanostructures by Self-Assembly of a Biomimetic β-Sheet-Rich Amyloidogenic Peptide

Squid sucker ring teeth (SRT) have emerged as a promising protein-only, thermoplastic biopolymer with an increasing number of biomedical and engineering applications demonstrated in recent years. SRT is a supra-molecular network whereby a flexible, amorphous matrix is mechanically reinforced by nanoconfined β-sheets. The building blocks for the SRT network are a family of suckerin proteins that share a common block copolymer architecture consisting of amorphous domains intervened by smaller, β-sheet forming modules. Recent studies have identified the peptide A1H1 (peptide sequence AATAVSHTTHHA) as one of the most abundant β-sheet forming domains within the suckerin protein family. However, we still have little understanding of the assembly mechanisms by which the A1H1 peptide may assemble into its functional load-bearing domains. In this study, we conduct a detailed self-assembly study of A1H1 and show that the peptide undergoes β-strands-driven elongation into amyloid-like fibrils with a rich polymorphism. The nanostructure of the fibrils was elucidated by small and wide-angle X-ray scattering (SAXS and WAXS) and atomic force microscopy (AFM). The presence of His-rich and Ala-rich segments results in an amphiphilic behavior and drives its assembly into fibrillar supramolecular chiral aggregates with helical ribbon configuration in solution, with the His-rich region exposed to the solvent molecules. Upon increase in concentration, the fibrils undergo gel formation, while preserving the same mesoscopic features. This complex phase behavior suggests that the repeat peptide modules of suckerins may be manipulated beyond their native biological environment to produce a wider variety of self-assembled amyloid-like nanostructures.

Modifying the Contact Angle of Anisotropic Cellulose Nanocrystals: Effect on Interfacial Rheology and Structure

Cellulose nanocrystals (CNCs) are an emerging natural material with the ability to stabilize fluid/fluid interfaces. Native CNC is hydrophilic and does not change the interfacial tension of the stabilized emulsion or foam system. In this study, rodlike cellulose particles were isolated from hemp and chemically modified to alter their hydrophobicity, i.e., their surface activity, which was demonstrated by surface tension measurements of the particles at the air/water interface. The buildup and mechanical strength of the interfacial structure were investigated using interfacial shear and dilatational rheometry. In contrast to most particle or protein-based interfacial adsorption layers, we observe in shear flow a Maxwellian behavior instead of a glasslike frequency response. The slow and reversible buildup of the layer and its unique frequency dependence indicate a weakly aggregated system, which depends on the hydrophobicity and, thus, on the contact angle of the CNC particles at the air/water interface. Exposed to dilatational flow, the weakly aggregated particles cluster and form compact structures. The interfacial structure generated by the different flow fields is characterized by the contact angle, immersion depth, and layer roughness obtained by neutron reflectometry with contrast variation while the size and local structural arrangement of the CNC particles were investigated by AFM imaging.

Nanoscale inhibition of polymorphic and ambidextrous IAPP amyloid aggregation with small molecules

Understanding how small molecules interface amyloid fibrils on the nanoscale is of importance for developing therapeutic treatment against amyloid-based diseases. Here we show, for the first time, that human islet amyloid polypeptide (IAPP) in the fibrillar form is polymorphic and ambidextrous possessing multiple periodicities. Upon interfacing with small molecule epigallocatechin gallate (EGCG), IAPP aggregation was rendered off pathway assuming the form of soft and disordered clusters, while mature IAPP fibrils displayed kinks and branching but conserved the twisted fibril morphology. These nanoscale phenomena resulted from competitive interactions between EGCG and the IAPP amyloidogenic region, as well as end capping of the fibrils by the small molecule. This information is crucial to delineating IAPP toxicity implicated in type 2 diabetes and developing new inhibitors against amyloidogenesis.

Nanocellulose Fragmentation Mechanisms and Inversion of Chirality from the Single Particle to the Cholesteric Phase

Understanding how nanostructure and nanomechanics influence physical material properties on the micro- and macroscale is an essential goal in soft condensed matter research. Mechanisms governing fragmentation and chirality inversion of filamentous colloids are of specific interest because of their critical role in load-bearing and self-organizing functionalities of soft nanomaterials. Here we provide a fundamental insight into the self-organization across several length scales of nanocellulose, an important biocolloid system with wide-ranging applications as structural, insulating, and functional material. Through a combined microscopic and statistical analysis of nanocellulose fibrils at the single particle level, we show how mechanically and chemically induced fragmentations proceed in this system. Moreover, by studying the bottom-up self-assembly of fragmented carboxylated cellulose nanofibrils into cholesteric liquid crystals, we show via direct microscopic observations that the chirality is inverted from right-handed at the nanofibril level to left-handed at the level of the liquid crystal phase. These results improve our fundamental understanding of nanocellulose and provide an important rationale for its application in colloidal systems, liquid crystals, and nanomaterials.

Polyphenol-Binding Amyloid Fibrils Self-Assemble into Reversible Hydrogels with Antibacterial Activity

Adaptable hydrogel networks with reversible connectivity have emerged as a promising platform for biomedical applications. Synthetic copolymers and low-molecular-weight gelators (LMWG) have been shown to form reversible hydrogels through self-assembly of the molecules driven by self-complementary hydrophobic interaction and hydrogen bonding. Here, inspired by the adhesive proteins secreted by mussels, we found that simply adding natural polyphenols, such as epigallocatechin gallate (EGCG) to amyloid fibrils present in the nematic phase, successfully drives the formation of hydrogels through self-assembly of the hybrid supramolecules. The hydrogels show birefringence under polarized light, indicating that the nematic orientation is preserved in the gel phase. Gel stiffness enhances with incubation time and with an increase in molecular ratios between polyphenol and fibrils, fibril concentration, and pH. The hydrogels are shear thinning and thermostable from 25 to 90 °C without any phase transition. The integrity of the trihydroxyl groups, the gallate ester moiety in EGCG, and the hydrophobicity of the polyphenols govern the interactions with the amyloid fibrils and thus the properties of the ensuing hydrogels. The EGCG-binding amyloid fibrils, produced from lysozyme and peptidoglycans, retain the main binding functions of the enzyme, inducing bacterial agglomeration and immobilization on both Gram-positive and Gram-negative bacteria. Furthermore, the antibacterial mechanism of the lysozyme amyloid fibril hydrogels is initiated by membrane disintegration. In combination with the lack of cytotoxicity to human colonic epithelial cells demonstrated for these hybrid supramolecules, a potential role in combating multidrug-resistant bacteria in biomedical applications is suggested, such as in targeting diseases related to infection of the small intestine.

Elasticity in Physically Cross-Linked Amyloid Fibril Networks

We provide a constitutive model of semiflexible and rigid amyloid fibril networks by combining the affine thermal model of network elasticity with the Derjaguin-Landau-Vervey-Overbeek (DLVO) theory of electrostatically charged colloids. When compared to rheological experiments on β-lactoglobulin and lysozyme amyloid networks, this approach provides the correct scaling of elasticity versus both concentration (G∼c^{2.2} and G∼c^{2.5} for semiflexible and rigid fibrils, respectively) and ionic strength (G∼I^{4.4} and G∼I^{3.8} for β-lactoglobulin and lysozyme, independent from fibril flexibility). The pivotal role played by the screening salt is to reduce the electrostatic barrier among amyloid fibrils, converting labile physical entanglements into long-lived cross-links. This gives a power-law behavior of G with I having exponents significantly larger than in other semiflexible polymer networks (e.g., actin) and carrying DLVO traits specific to the individual amyloid fibrils.

Biophotonics of Native Silk Fibrils

Native silk fibroin (NSF) is a unique biomaterial with extraordinary mechanical and biochemical properties. These key characteristics are directly associated with the physical transformation of unstructured, soluble NSF into highly organized nano- and microscale fibrils rich in β-sheet content. Here, it is shown that this NSF fibrillation process is accompanied by the development of intrinsic fluorescence in the visible range, upon near-UV excitation, a phenomenon that has not been investigated in detail to date. Here, the optical and fluorescence characteristics of NSF fibrils are probed and a route for potential applications in the field of self-assembled optically active biomaterials and systems is explored. In particular, it is demonstrated that NSF can be structured into autofluorescent microcapsules with a controllable level of β-sheet content and fluorescence properties. Furthermore, a facile and efficient fabrication route that permits arbitrary patterns of NSF microcapsules to be deposited on substrates under ambient conditions is shown. The resulting fluorescent NSF patterns display a high level of photostability. These results demonstrate the potential of using native silk as a new class of biocompatible photonic material.

Cofibrillization of Pathogenic and Functional Amyloid Proteins with Gold Nanoparticles against Amyloidogenesis

Biomimetic nanocomposites and scaffolds hold the key to a wide range of biomedical applications. Here we show, for the first time, a facile scheme of cofibrillizing pathogenic and functional amyloid fibrils via gold nanoparticles (AuNPs) and their applications against amyloidogenesis. This scheme was realized by β-sheet stacking between human islet amyloid polypeptide (IAPP) and the β-lactoglobulin "corona" of the AuNPs, as revealed by transmission electron microscopy, 3D atomic force microscopy, circular dichroism spectroscopy, and molecular dynamics simulations. The biomimetic AuNPs eliminated IAPP toxicity, enabled X-ray destruction of IAPP amyloids, and allowed dark-field imaging of pathogenic amyloids and their immunogenic response by human T cells. In addition to providing a viable new nanotechnology against amyloidogenesis, this study has implications for understanding the in vivo cross-talk between amyloid proteins of different pathologies.

Squid Suckerin Biomimetic Peptides Form Amyloid-like Crystals with Robust Mechanical Properties

We present the self-assembly of fibers formed from a peptide sequence (A1H1) derived from suckerin proteins of squid sucker ring teeth (SRT). SRT are protein-only biopolymers with an unconventional set of physicochemical and mechanical properties including high elastic modulus coupled with thermoplastic behavior. We have identified a conserved peptide building block from suckerins that possess the ability to assemble into materials with similar mechanical properties as the native SRT. A1H1 displays amphiphilic characteristics and self-assembles from the bottom-up into mm-scale fibers initiated by the addition of a polar aprotic solvent. A1H1 fibers are thermally resistant up to 239 °C, coupled with an elastic modulus of ∼7.7 GPa, which can be explained by the tight packing of β-sheet-enriched crystalline building blocks as identified by wide-angle X-ray scattering (WAXS), with intersheet and interstrand distances of 5.37 and 4.38 Å, respectively. A compact packing of the peptides at their Ala-rich terminals within the fibers was confirmed from molecular dynamics simulations, and we propose a hierarchical model of fiber assembly of the mature peptide fiber.

Competition between crystal and fibril formation in molecular mutations of amyloidogenic peptides

Amyloidogenic model peptides are invaluable for investigating assembly mechanisms in disease related amyloids and in protein folding. During aggregation, such peptides can undergo bifurcation leading to fibrils or crystals, however the mechanisms of fibril-to-crystal conversion are unclear. We navigate herein the energy landscape of amyloidogenic peptides by studying a homologous series of hexapeptides found in animal, human and disease related proteins. We observe fibril-to-crystal conversion occurring within single aggregates via untwisting of twisted ribbon fibrils possessing saddle-like curvature and cross-sectional aspect ratios approaching unity. Changing sequence, pH or concentration shifts the growth towards larger aspect ratio species assembling into stable helical ribbons possessing mean-curvature. By comparing atomistic calculations of desolvation energies for association of peptides we parameterise a kinetic model, providing a physical explanation of fibril-to-crystal interconversion. These results shed light on the self-assembly of amyloidogenic peptides, suggesting amyloid crystals, not fibrils, represent the ground state of the protein folding energy landscape.

Aggregation of amyloidogenic peptides into fibrils and crystals has incidence in several amyloid-related diseases. Here, the authors investigate the origins of the fibril-to-crystal conversion in amyloidogenic hexapeptides pointing to the amyloid crystals as the ground state in the protein folding energy landscape.

Absolute Quantification of Amyloid Propagons by Digital Microfluidics

The self-replicating properties of proteins into amyloid fibrils is a common phenomenon and underlies a variety of neurodegenerative diseases. Because propagation-active fibrils are chemically indistinguishable from innocuous aggregates and monomeric precursors, their detection requires measurements of their replicative capacity. Here we present a digital amyloid quantitative assay (d-AQuA) with insulin as model protein for the absolute quantification of single replicative units, propagons. D-AQuA is a microfluidics-based technology that performs miniaturized simultaneous propagon-induced amplification chain reactions within hundreds to thousands of picoliter-sized droplets. At limiting dilutions, the d-AQuA reactions follow a stochastic regime indicative of the detection of single propagons. D-AQuA thus enables absolute quantification of single propagons present in a given sample at very low concentrations. The number of propagons quantified by d-AQuA was similar to that of fibrillar insulin aggregates detected by atomic-force microscopy and to an equivalent microplate-based assay, providing independent evidence for the identity of insulin propagons with a subset of morphologically defined protein aggregates. The sensitivity, precision, and accuracy of d-AQuA enable it to be suitable for multiple biotechnological and medical applications.

Gelatin-Graphene Nanocomposites with Ultralow Electrical Percolation Threshold

Gelatin-graphene conductive biopolymer nanocomposites (CPCs) with ultralow percolation threshold are designed by reducing in situ graphene oxide nanosheets with ascorbic acid and suppressing the aggregation of the graphene nanosheets. The resulting conductive nanocomposites show a record-low electrical percolation threshold of 3.3 × 10(-2) vol%, which arises from the homogeneous dispersion of the graphene nanosheets within the gelatin matrix.

Continuous Paranematic Ordering of Rigid and Semiflexible Amyloid-Fe3O4 Hybrid Fibrils in an External Magnetic Field

External magnetic field is a powerful approach to induce orientational order in originally disordered suspensions of magneto-responsive anisotropic particles. By small angle neutron scattering and optical birefringence measurement technology, we investigated the effect of magnetic field on the spatial ordering of hybrid amyloid fibrils with different aspect ratios (length-to-diameter) and flexibilities decorated by spherical Fe3O4 nanoparticles. A continuous paranematic ordering from an initially isotropic suspension was observed upon increasing magnetic field strength, with spatial orientation increasing with colloidal volume fraction. At constant dimensionless concentration, stiff hybrid fibrils with varying aspect ratios and volume fractions, fall on the same master curve, with equivalent degrees of ordering at identical magnetic fields. However, the semiflexible hybrid fibrils with contour length close to persistence length exhibit a lower degree of alignment. This is consistent with Khokhlov-Semenov theoretical predictions. These findings sharpen the experimental toolbox to design colloidal systems with controllable degree of orientational ordering.

Freeze-Thaw Cycling Induced Isotropic-Nematic Coexistence of Amyloid Fibrils Suspensions

Amyloid fibrils are charged semiflexible assemblies with very large aspect ratio (length to diameter, L/D). Because of this large aspect ratio, the isotropic (I) and nematic (N) phase coexistence expected from the first-order thermodynamic nature of the I-N phase transition, as predicted from the Onsager's theory, is vanishingly small and, in practice, challenging to experimentally observe. In this study we present a remarkable widening of the I + N biphasic region in β-lactoglobulin fibrils suspension via freeze-thaw (F-T) cycling. The demixing behavior can be induced and controlled by a slow growth of propagation front of the ice crystals, which grow by excluding the amyloid fibrils from the crystal phase and thus concentrating them in the liquid phase. The growth of the ice crystals is accompanied by the formation of concentrated and elongated tactoid-like structure in the liquid phase. During the subsequent thawing cycling, at large tactoid domains, the mismatch in density caused by the presence of amyloid fibrils is sufficient to generate a sedimentation of the N phase at the bottom of the vial, coexisting with an I phase on the top. We reason why, despite the remarkable stability of the coexisting I and N phases observed over several weeks after F-T cycling, the biphasic region is understood to be a nonequilibrium, metastable state. Yet, the results in this study suggest that the F-T treatment is an effective approach to stabilize multiphase coexistence of liquid crystalline phases in colloidal suspensions of anisotropic particles without the need of additives, such as depleting agents, needed to modify interaction potentials.

Mechanically Enhanced Liquid Interfaces at Human Body Temperature Using Thermosensitive Methylated Nanocrystalline Cellulose

The mechanical performance of materials at oil/water interfaces after consumption is a key factor affecting hydrophobic drug release. In this study, we methylated the surface of nanocrystalline cellulose (NCC) by mercerization and dimethyl sulfate exposure to produce thermosensitive biopolymers. These methylated NCC (metNCC) were used to investigate interfacial thermogelation at air/water and medium-chain triglyceride (MCT)/water interfaces at body temperature. In contrast to bulk fluid dynamics, elastic layers were formed at room temperature, and elasticity increased significantly at body temperature, which was measured by interfacial shear and dilatational rheology in situ. This unique phenomenon depends on solvent quality, temperature, and polymer concentration at interfaces. Thus, by adjusting the degree of hydrophobicity of metNCC, the interfacial elasticity and thermogelation of the interfaces could be varied. In general, these new materials (metNCC) formed more brittle interfacial layers compared to commercial methylcellulose (MC A15). Thermogelation of methylcellulose promotes attractive intermolecular forces, which were reflected in a change in self-assembly of metNCC at the interface. As a consequence, layer thickness and density increased as a function of temperature. These effects were measured by atomic force microscopy (AFM) images of the displaced interface and confirmed by neutron reflection. The substantial structural and mechanical change of methylcellulose interfaces at body temperature represents a controllable encapsulation parameter allowing optimization of lipid-based drug formulations.

Hybrid Amyloid Membranes for Continuous Flow Catalysis

Amyloid fibrils are promising nanomaterials for technological applications such as biosensors, tissue engineering, drug delivery, and optoelectronics. Here we show that amyloid-metal nanoparticle hybrids can be used both as efficient active materials for wet catalysis and as membranes for continuous flow catalysis applications. Initially, amyloid fibrils generated in vitro from the nontoxic β-lactoglobulin protein act as templates for the synthesis of gold and palladium metal nanoparticles from salt precursors. The resulting hybrids possess catalytic features as demonstrated by evaluating their activity in a model catalytic reaction in water, e.g., the reduction of 4-nitrophenol into 4-aminophenol, with the rate constant of the reduction increasing with the concentration of amyloid-nanoparticle hybrids. Importantly, the same nanoparticles adsorbed onto fibrils surface show improved catalytic efficiency compared to the same unattached particles, pointing at the important role played by the amyloid fibril templates. Then, filter membranes are prepared from the metal nanoparticle-decorated amyloid fibrils by vacuum filtration. The resulting membranes serve as efficient flow catalysis active materials, with a complete catalytic conversion achieved within a single flow passage of a feeding solution through the membrane.