ILQINS Hexapeptide, Identified in Lysozyme Left-Handed Helical Ribbons and Nanotubes, Forms Right-Handed Helical Ribbons and Crystals

Cell invasive amyloid assemblies from SARS-CoV-2 peptides can form multiple polymorphs with varying neurotoxicity

The neurological symptoms of COVID-19, often referred to as neuro-COVID include neurological pain, memory loss, cognitive and sensory disruption. These neurological symptoms can persist for months and are known as Post-Acute Sequalae of COVID-19 (PASC). The molecular origins of neuro-COVID, and how it contributes to PASC are unknown, however a growing body of research highlights that the self-assembly of protein fragments from SARS-CoV-2 into amyloid nanofibrils may play a causative role. Previously, we identified two fragments from the SARS-CoV-2 proteins, Open Reading Frame (ORF) 6 and ORF10, that self-assemble into neurotoxic amyloid assemblies. Here we further our understanding of the self-assembly mechanisms and nano-architectures formed by these fragments and their biological responses. By solubilising the peptides in a fluorinated solvent, we eliminate insoluble aggregates in the starting materials (seeds) that change the polymorphic landscape of the assemblies. The resultant assemblies are dominated by structures with higher free energies (e.g. ribbons and amorphous aggregates) that are less toxic to cultured neurons but do affect their mitochondrial respiration. We also show the first direct evidence of cellular uptake of viral amyloids. This work highlights the importance of understanding the polymorphic behaviour of amyloids and the correlation to neurotoxicity, particularly in the context of neuro-COVID and PASC.

Close Packing in Trans Conformers Promotes the Formation of Supramolecular Structures with C1 Symmetry

Assemblies with C1 symmetry exhibit important applications in many fields such as enantioselective catalysis. However, their formation is challenging due to their large entropic disadvantage, and molecular information on their formation dynamics is limited because of the lack of effective characterization techniques. Here, using achiral amphiphilic molecules such as N-oleoyl ethanolamide (OEA) and its analogues as modeling assembly units, we demonstrated that the sss polarization signals, generated by femtosecond sum frequency generation vibrational spectroscopy (SFG-VS), provide a powerful tool to monitor the formation dynamics of the C1 symmetric supramolecular structures at the interfaces. The trans conformation of the assembly units can provide strong π-π interactions and thus produce enough enthalpy to drive the formation of C1 symmetric supramolecular structures. However, the cis conformation impedes the assembly of C1 symmetric structures and cannot generate sss and chiral polarization SFG signals. These findings may aid in rationally constructing ordered and functional superstructures and understanding the mechanism of chirality formation.

Chiral inversion induced by aromatic interactions in short peptide assembly

Although hydrophobic interactions provide the main driving force for initial peptide aggregation, their role in regulating suprastructure handedness of higher-order architectures remains largely unknown. We here interrogate the effects of hydrophobic amino acids on handedness at various assembly stages of peptide amphiphiles. Our studies reveal that relative to aliphatic side chains, aromatic side chains set the twisting directions of single β-strands due to their strong steric repulsion to the backbone, and upon packing into multi-stranded β-sheets, the side-chain aromatic interactions between strands form the aromatic ladders with a directional preference. This ordering not only leads to parallel β-sheet arrangements but also induces the chiral flipping over of single β-strands within a β-sheet. In contrast, the lack of orientational hydrophobic interactions in the assembly of aliphatic peptides implies no chiral inversion upon packing into β-sheets. This study opens an avenue to harness peptide aggregates with targeted handedness via aromatic side-chain interactions.

Supramolecular Hydrogels and Water Channels of Differing Diameters from Dipeptide Isomers

Dipeptides stereoisomers and regioisomers composed of norleucine (Nle) and phenylalanine (Phe) self-assemble into hydrogels under physiological conditions that are suitable for cell culture. The supramolecular behavior, however, differs as the packing modes comprise amphipathic layers or water channels, whose diameter is defined by either four or six dipeptide molecules. A variety of spectroscopy, microscopy, and synchrotron-radiation-based techniques unveil fine details of intermolecular interactions that pinpoint the relationship between the chemical structure and ability to form supramolecular architectures that define soft biomaterials.

Lung endothelium, tau, and amyloids in health and disease

Lung endothelia in the arteries, capillaries, and veins are heterogeneous in structure and function. Lung capillaries in particular represent a unique vascular niche, with a thin yet highly restrictive alveolar-capillary barrier that optimizes gas exchange. Capillary endothelium surveys the blood while simultaneously interpreting cues initiated within the alveolus and communicated via immediately adjacent type I and type II epithelial cells, fibroblasts, and pericytes. This cell-cell communication is necessary to coordinate the immune response to lower respiratory tract infection. Recent discoveries identify an important role for the microtubule-associated protein tau that is expressed in lung capillary endothelia in the host-pathogen interaction. This endothelial tau stabilizes microtubules necessary for barrier integrity, yet infection drives production of cytotoxic tau variants that are released into the airways and circulation, where they contribute to end-organ dysfunction. Similarly, beta-amyloid is produced during infection. Beta-amyloid has antimicrobial activity, but during infection it can acquire cytotoxic activity that is deleterious to the host. The production and function of these cytotoxic tau and amyloid variants are the subject of this review. Lung-derived cytotoxic tau and amyloid variants are a recently discovered mechanism of end-organ dysfunction, including neurocognitive dysfunction, during and in the aftermath of infection.

Unravelling the non-classical nucleation mechanism of an amyloid nanosheet through atomic force microscopy and an infrared probe technique

Understanding the amyloid nucleation mechanism is fundamentally important for the development of diagnostics and therapeutics of amyloid-related diseases and for the design and application of amyloid-based materials. To this end, we here explore the use of atomic force microscopy (AFM) and a side-chain-based infrared (IR) probe technique to investigate the amyloid nanosheet formation mechanism of an Aβ16-22 variant, KLVFXAK, where X is p-cyanophenylalanine with its side-chain cyano group being an infrared probe. Using AFM, we reveal that the formation of KLVFXAK amyloid nanosheets follows a two-step non-classical nucleation mechanism. The first step is the rapid formation of a metastable fibrillar intermediate and the second step is slow transformation to the final nanosheet. Using the side-chain-based IR probe technique, we obtain spectroscopic evidence for the proposed nucleation mechanism of the amyloid nanosheet as well as the structural details for the intermediate and amyloid nanosheet. By using the structural constraints set by the two techniques, we propose the structural models for both the fibrillar intermediate and the amyloid nanosheet. In addition, we further investigated the amyloid nanosheet formation mechanism of a similar Aβ16-22 variant, KLVFXAE, and showed the impact of mutation on the amyloid nucleation mechanism. Our work also provides a nice example of how to use the combined approach of AFM and a side-chain-based IR probe technique to unravel the complex nucleation mechanism of amyloid formation.

One-pot asymmetric living copolymerization-induced chiral self-assemblies and circularly polarized luminescence

Controlled synthesis of conjugated block polymers enables the optimization of their self-assembly and may lead to distinct optical properties and functionalities. Herein, we report a direct chain extension of one-handed helical poly(acyl methane) with 1-ethynyl-4-iodo-2,5-bis(octyloxy)benzene, affording well-defined π-conjugated poly(acyl methane)-b-poly(phenylene ethynylene) copolymers. Although the distinct monomers are polymerized via different mechanisms, the one-pot copolymerization follows a living polymerization manner, giving the desired optically active block copolymers with controllable molar mass and low distribution. The block copolymerization induced chiral self-assembly simultaneously due to the one-handed helicity of the poly(acyl methane) block, giving spherical nanoparticles, one-handed helices, and chiral micelles with controlled dimensions regarding the composition of the generated copolymers. Interestingly, the chiral assemblies exhibit clear circularly polarized luminescence with tunable handedness and a high dissymmetric factor.

Structural Colors from Amyloid-Based Liquid Crystals

The helical periodicity and layered structure in cholesteric liquid crystals (CLCs) may be tuned to generate structural color according to the Bragg's law of diffraction. A wide range of natural-based materials such as condensed DNA, collagen, chitin, cellulose, and chiral biopolymers exhibit cholesteric phases with left-handed helixes and ensued structural colors. Here, the possibility of using amyloid CLCs is reported to prepare films with iridescent color reflection and opposite handedness. Right-handed CLCs assembled by left-handed amyloid fibrils are dried into layered structures with variable pitch controlled by the addition of glucose. Circularly polarized light with the same handedness of amyloid CLCs helix is reflected in the Bragg regime. Varying the drying speed leads to the switching between films with a rainbow-like color gradient and large area uniform color. It is confirmed that the origin of the colors derives from the layered structures of the amyloid CLCs, given the negligeable birefringence of the films, calculated from optical rotatory dispersion. These findings provide a facile approach to constructing biosourced cholesteric materials and introduce an original class of proteinaceous materials for the generation of structural colors from right-handed circularly polarized light.

Controlling 1D Nanostructures and Handedness by Polar Residue Chirality of Amphiphilic Peptides

Peptide assemblies are promising nanomaterials, with their properties and technological applications being highly hinged on their supramolecular architectures. Here, how changing the chirality of the terminal charged residues of an amphiphilic hexapeptide sequence Ac-I4 K2 -NH2 gives rise to distinct nanostructures and supramolecular handedness is reported. Microscopic imaging and neutron scattering measurements show thin nanofibrils, thick nanofibrils, and wide nanotubes self-assembled from four stereoisomers. Spectroscopic and solid-state nuclear magnetic resonance (NMR) analyses reveal that these isomeric peptides adopt similar anti-parallel β-sheet secondary structures. Further theoretical calculations demonstrate that the chiral alterations of the two C-terminal lysine residues cause the formation of diverse single β-strand conformations, and the final self-assembled nanostructures and handedness are determined by the twisting direction and degree of single β-strands. This work not only lays a useful foundation for the fabrication of diverse peptide nanostructures by manipulating the chirality of specific residues but also provides a framework for predicting the supramolecular structures and handedness of peptide assemblies from single molecule conformations.

Protein Nanotubes as Advanced Material Platforms and Delivery Systems

Protein nanotubes (PNTs) as state-of-the-art nanocarriers are promising for various potential applications both in the food and pharmaceutical industries. Derived from edible starting sources like α-lactalbumin, lysozyme, and ovalbumin, PNTs bear properties of biocompatibility and biodegradability. Their large specific surface area and hydrophobic core facilitate chemical modification and loading of bioactive substances, respectively. Moreover, their enhanced permeability and penetration ability across biological barriers such as intestinal mucus, extracellular matrix, and thrombus clot, make it promising platforms for health-related applications. Most importantly, their simple preparation processes enable large-scale production, supporting applications in the biomedical and nanotechnological fields. Understanding the self-assembly principles is crucial for controlling their morphology, size, and shape, and thus provides the ground to a multitude of applications. Here, the current state-of-the-art of PNTs including their building materials, physicochemical properties, and self-assembly mechanisms are comprehensively reviewed. The advantages and limitations, as well as challenges and prospects for their successful applications in biomaterial and pharmaceutical sectors are then discussed and highlighted. Potential cytotoxicity of PNTs and the need of regulations as critical factors for enabling in vivo applications are also highlighted. In the end, a brief summary and future prospects for PNTs as advanced platforms and delivery systems are included.

Purification of Egg White Lysozyme Determines the Downstream Fibrillation of Protein and Co-assembly with Phytochemicals to Form Edible Hydrogels Regulating the Lipid Metabolism

Although the synthetic chemistry or synthetic biological systems have already shown the power of biomaterials engineering, natural bioresource matter is still a valuable library of raw ingredients for the production of biomaterials, in particular, the edible ones. However, the influence of upstream isolation and purification of the raw materials on their performance in the downstream processing procedures is still unexplored, which is essential for the engineering of biomaterials. Based on the comparison of conventional techniques, heating-induced precipitation combined with resin-blending ion exchange was developed as a simple and cheap method for the utilization of egg whites to produce the lysozyme that is found to be exclusively feasible for fibrillation. Even with similar purities, only the lysozyme prepared by this method could be utilized to form ordered linear aggregate fibrils. Fibrillation was recently pursued as a new approach to utilize bioresource mass for high-tech end-products. Phytochemicals, totally replacing salts, induced the lysozyme fibrils to form hydrogels spontaneously, which was further demonstrated in an in vivo study to prevent obesity induced by a high-fat diet (HFD) by reducing lipid absorption and lipogenesis, promoting energy expenditure, and inhibiting inflammation. The agri-food bioresource was successfully employed as a proof of concept in edible biomedical materials for the regulation of lipid metabolism.

Supramolecular Chiral Assembly of Symmetric Molecules with an Extended Conjugated Core

C3-symmetric molecules carrying a conjugated diacetylene (DA) core are found to self-assemble into well-defined supramolecular fibers with enhanced supramolecular chirality in both organic and aqueous solutions. The conjugated core affords these amphiphiles characteristic fluorescence properties, which can be quenched partially due to the aggregation. Integration of the C3-symmetry with the conjugation provides these novel molecules strong aggregation tendency through solvent-mediated π-π stacking with preferential supramolecular chirality, which is predominately related to steric hindrance from their dipeptide pendants. Highly uniform supramolecular fibers of P and M handedness with thickness consistent in the dimensions of individual C3 molecules are obtained. The increase of concentrations induces these fibers to wrap together to form supramolecular fibrous bundles. Topochemical polymerization of the DA moieties can transform these supramolecular fibers into stable covalent polymers. We therefore believe that self-assembly of these C3-symmetric molecules with extended conjugated DA cores provides new prospects for the construction of supramolecular helical fibers through enhanced π-π stacking and creates a convenient strategy to furnish covalent chiral polymers of hierarchical structures through supramolecular assembly.

Bottom-Up Approach to Understand Chirality Transfer across Scales in Cellulose Assemblies

Cellulose is a polysaccharide that displays chirality across different scales, from the molecular to the supramolecular level. This feature has been exploited to generate chiral materials. To date, the mechanism of chirality transfer from the molecular level to higher-order assemblies has remained elusive, partially due to the heterogeneity of cellulose samples obtained via top-down approaches. Here, we present a bottom-up approach that uses well-defined cellulose oligomers as tools to understand the transfer of chirality from the single oligomer to supramolecular assemblies beyond the single cellulose crystal. Synthetic cellulose oligomers with defined sequences self-assembled into thin micrometer-sized platelets with controllable thicknesses. These platelets further assembled into bundles displaying intrinsic chiral features, directly correlated to the monosaccharide chirality. Altering the stereochemistry of the oligomer termini impacted the chirality of the self-assembled bundles and thus allowed for the manipulation of the cellulose assemblies at the molecular level. The molecular description of cellulose assemblies and their chirality will improve our ability to control and tune cellulose materials. The bottom-up approach could be expanded to other polysaccharides whose supramolecular chirality is less understood.

Ultrasound-induced protein restructuring and ordered aggregation to form amyloid crystals

Amyloid crystals, a form of ordered protein aggregates documented relatively recently, have not been studied as extensively as amyloid fibres. This study investigates the formation of amyloid crystals with low frequency ultrasound (20 kHz) using β-lactoglobulin, as a model protein for amyloid synthesis. Acoustic cavitation generates localised zones of intense shear, with extreme heat and pressure that could potentially drive the formation of amyloid structures at ambient bulk fluid temperatures (20 ± 1 °C). Thioflavin T fluorescence and electron microscopy showed that low-frequency ultrasound at 20 W/cm3 input power induced β-stacking to produce amyloid crystals in the mesoscopic size range, with a mean length of approximately 22 µm. FTIR spectroscopy indicated a shift towards increased intermolecular antiparallel β-sheet content. An increase in sonication time (0-60 min) and input power (4-24 W/cm3) increased the mean crystal length, but this increase was not linearly proportional to sonication time and input power due to the delayed onset of crystal growth. We propose that acoustic cavitation causes protein unfolding and aggregation and imparts energy to aggregates to cross the torsion barrier, to achieve their lowest energy state as amyloid crystals. The study contributes to a further understanding of protein chemistry relating to the energy landscape of folding and aggregation. Ultrasound presents opportunities for practical applications of amyloid structures, presenting a more adaptable and scalable approach for synthesis.

Neurotoxic amyloidogenic peptides in the proteome of SARS-COV2: potential implications for neurological symptoms in COVID-19

COVID-19 is primarily known as a respiratory disease caused by SARS-CoV-2. However, neurological symptoms such as memory loss, sensory confusion, severe headaches, and even stroke are reported in up to 30% of cases and can persist even after the infection is over (long COVID). These neurological symptoms are thought to be produced by the virus infecting the central nervous system, however we don't understand the molecular mechanisms triggering them. The neurological effects of COVID-19 share similarities to neurodegenerative diseases in which the presence of cytotoxic aggregated amyloid protein or peptides is a common feature. Following the hypothesis that some neurological symptoms of COVID-19 may also follow an amyloid etiology we identified two peptides from the SARS-CoV-2 proteome that self-assemble into amyloid assemblies. Furthermore, these amyloids were shown to be highly toxic to neuronal cells. We suggest that cytotoxic aggregates of SARS-CoV-2 proteins may trigger neurological symptoms in COVID-19.

Chirality-Dependent Copper-Diphenylalanine Assemblies with Tough Layered Structure and Enhanced Catalytic Performance

Chiral regulation to prepare functional materials has aroused considerable interest in recent years. However, little is known on the effect of chirality of ligands in the metal-organic coordination assembly process. We report the self-assembly of diphenylalanine peptide (Phe-Phe, FF), the core fragment of Aβ protein, with metal copper ion (Cu²⁺) into metal-organic assemblies with chirality-encoded structures and properties. The chirality-dependent metal-dipeptide assembles with different morphologies and supramolecular chirality were obtained by facile changing of the FF chirality. Single-crystal results indicate that (L)-FF coordinated with Cu²⁺ into a cross-chain structure with a five-coordinated style, while the racemates of (L+D)-FF with Cu²⁺ crystallized into an (L)-Cu²⁺-(D)-Cu²⁺ alternated four-coordinating structure, enabling a higher mechanical and catalytic performance. The Young's modulus of (L+D)-FF-Cu is as high as 34.36 GPa, which is 2.45 times higher than that of (L)-FF-Cu. Furthermore, both of them follow the characteristic enzyme kinetics and show higher catalytic activity than natural laccase at the same mass concentration. Specifically, the calculated catalytic efficiency (k_cat/K_M) of (L+D)-FF-Cu is 1.14 times higher than that of (L)-FF-Cu, and the (L+D)-FF-Cu shows significantly enhanced stability and reusability compared with (L)-FF-Cu. The results reveal that highly functional materials could be constructed by encoding the chirality of molecular building blocks.

Molecular Insight into the β-Sheet Twist and Related Morphology of Self-Assembled Peptide Amphiphile Ribbons

Self-assembly of high-aspect-ratio filaments containing β-sheets has attracted much attention due to potential use in bioengineering and biomedicine. However, precisely predicting the assembled morphologies remains a grand challenge because of insufficient understanding of the self-assembly process. We employed an atomistic model to study the self-assembly of peptide amphiphiles (PAs) containing valine-glutamic acid (VE) dimeric repeats. By changing of the sequence length, the assembly morphology changes from flat ribbon to left-handed twisted ribbon, implying a relationship between β-sheet twist and strength of interstrand hydrogen bonds. The calculations are used to quantify this relationship including both magnitude and sign of the ribbon twist angle. Interestingly, a change in chirality is observed when we introduce the RGD epitope into the C-terminal of VE repeats, suggesting arginine and glycine's role in suppressing right-handed β-sheet formation. This study provides insight into the relationship between β-sheet twist and self-assembled nanostructures including a possible design rule for PA self-assembly.

Precise Synthesis of π-Conjugated Block Copolymers and Polymerization-Induced Chiral Self-Assembly toward Helical Nanofibers with Circularly Polarized Luminescence

Precise synthesis and efficient self-assembly of semiconducting polymers are of great interest. Herein, we report the controlled synthesis of π-conjugated poly(phenyl isocyanide)-b-poly(phenyleneethylene) (PPI-b-PPE) copolymers via chain extension of ethynyl 4-iodobenzene initiated by Pd(II)-terminated helical poly(phenyl isocyanide) (PPI). The in-situ-generated block copolymers self-assembled into various supramolecular architectures depending on the PPE length. The helical PPI segment induced the block copolymers with an appropriate PPE length self-assemble into helical nanofibers with a controlled size and defined helicity. Interestingly, the chiral assemblies of the block copolymers exhibit intense optical activity and emit clear circularly polarized luminescence.

A crosslinked colloidal network of peptide/nucleic base amphiphiles for targeted cancer cell encapsulation

The use of peptide amphiphiles (PAs) is becoming increasingly popular, not only because of their unique self-assembly properties but also due to the versatility of designs, allowing biological responsiveness, biocompatibility, and easy synthesis, which could potentially contribute to new drug design and disease treatment concepts. Oligonucleotides, another major functional bio-macromolecule class, have been introduced recently as new functional building blocks into PAs, further enriching the tools available for the fabrication of bio-functional PAs. Taking advantage of this, in the present work, two nucleic base-linked (adenine, A and thymine, T) RGD-rich peptide amphiphiles (NPAs) containing the fluorophores naphthalimide and rhodamine (Nph-A and Rh-T) were designed and synthesized. The two NPAs exhibit distinctive assembly behaviours with spherical (Rh-T) and fibrous (Nph-A) morphologies, and mixing Nph-A with Rh-T leads to a densely crosslinked colloidal network (Nph-A/Rh-T) via mutually promoted supramolecular polymerization via nucleation-growth assembly. Because of the RGD-rich sequences in the crosslinked network, further research on in situ targeted cancer cell (MDA-MB-231) encapsulation via RGD-integrin recognition was performed, and the modulation of cell behaviours (e.g., cell viability and migration) was demonstrated using both confocal laser scanning microscopy (CLSM) imaging and a scratch wound healing assay.

Chirality Effects in Peptide Assembly Structures

Peptide assembly structures have been widely exploited in fabricating biomaterials that are promising for medical applications. Peptides can self-organize into various highly ordered supramolecular architectures, such as nanofibril, nanobelt, nanotube, nanowire, and vesicle. Detailed studies of the molecular mechanism by which these versatile building blocks assemble can guide the design of peptide architectures with desired structure and functionality. It has been revealed that peptide assembly structures are highly sequence-dependent and sensitive to amino acid composition, the chirality of peptide and amino acid residues, and external factors, such as solvent, pH, and temperature. This mini-review focuses on the regulatory effects of chirality alteration on the structure and bioactivity of linear and cyclic peptide assemblies. In addition, chiral self-sorting and co-assembly of racemic peptide mixtures were discussed.

Self-Templated, Enantioselective Assembly of an Amyloid-like Dipeptide into Multifunctional Hierarchical Helical Arrays

Chiral self-assembly of peptides has attracted great interest owing to their promising applications in biomedicine, chemistry, and materials science. However, compared with the rich knowledge about their chiral self-assembly at the molecular or nanoscale, the formation of long-range-ordered hierarchical helical arrays (HHAs) from simple peptides remains a formidable challenge. Herein, we report the self-templated assembly of an amyloid-like dipeptide into long-range-ordered HHAs by their spontaneous fibrillization and hierarchical helical assembly within a confined film. The chiral interactions between the peptide and diamines result in geometry frustration and the phase transition of self-assembling peptide films from achiral spherulite structures into chiral HHAs. By changing the chirality and enantioselective interactions, we can control the phase behavior, handedness, and chiroptics of the self-assembled HHAs precisely. Moreover, the redox activity of the HHAs allows the in situ decoration of nanoparticles with high catalytic activity. These results provide insights into the chiral self-assembly of peptides and the fabrication of highly ordered materials with complex architectures and promising applications in chiroptics and catalysis.

Unexpected Role of Achiral Glycine in Determining the Suprastructural Handedness of Peptide Nanofibrils

Helical supramolecular architectures play important structural and functional roles in biological systems. Although their occurrence is widely perceived to correlate to fundamental chiral units including l-amino acids and d-sugars, the detailed relationship between molecular and supramolecular handedness is still unclear. At the same time, although achiral units are practically always in close proximity to chiral ones by covalent linkage along a polymeric chain, their effect on supramolecular handedness has received relatively less attention. Here, we designed a set of short amphiphilic peptides, in which an achiral glycine residue was incorporated at the interface between the hydrophobic and hydrophilic segments. We observed that glycine incorporation caused dramatic variations in suprastructural handedness in self-assembled peptide nanofibrils, and the effect of the hydrophilic charged residue at the C-terminus on supramolecular handedness was demolished, leading to chiral truncation. Furthermore, molecular dynamics simulations and quantum chemistry calculations revealed that the unanticipated role of the glycine residue in regulating supramolecular handedness originated from its effect on the conformational preference of single β-strands. Importantly, reduced density gradient analyses on single β-strands indicated that, due to the lack of a side chain in glycine, intricate noncovalent interactions were produced among the neighboring amino acid side chains of the incorporated glycine and its local backbone, resulting in diverse β-strand conformations.

Self-Assembly of Ferrocenyl Phenylalanine into Nanohelical Arrays via Kinetic Control

The spontaneous alignment of self-assembled chiral nanostructures at macroscopic scales is appealing because of their unique structural features and physicochemical properties. Here we present the construction of highly ordered bioorganometallic nanohelical arrays on the basis of the hierarchical chiral self-assembly of the simple ferrocenyl l-phenylalanine (Fc-l-F). The formation of nanohelical arrays is under kinetic control, which can be controlled by changing the growth time and the vapor temperature. The chiral nanoarrays can generate circularly polarized luminescence by the incorporation of fluorescent dyes. Moreover, due to the redox activity of the Fc moiety, the nanohelical arrays show enhanced electrical capacity compared with previously reported peptide nanomaterials. The results shed light on the highly ordered chiral self-assembled nanomaterials, which have potential applications in fields of optics, sensing, and energy storage.

Co-assembly and multicomponent hydrogel formation upon mixing nucleobase-containing peptides

Peptide-based hydrogels are physical gels formed through specific supramolecular self-assembling processes, leading to ordered nanostructures which constitute the water entrapping scaffold of the soft material. Thanks to the inherent properties of peptides, these hydrogels are highly considered in the biomedical domain and open new horizons in terms of application in advanced therapies and biotechnologies. The use of one, and only one, native peptide to formulate a gel is by far the most reported approach to design such materials, but suffers from several limitations, including in terms of mechanical properties. To improve peptide-based hydrogels interest and give rise to innovative properties, several strategies have been proposed in the recent years, and the development of multicomponent peptide-based hydrogels appears as a promising and relevant strategy. Indeed, mixing two or more compounds to develop new materials is a much-used approach that has proven its effectiveness in a wide variety of domains, including polymers, composites and alloys. While still limited to a handful of examples, we would like to report herein on the formulation and the comprehensive study of multicomponent hybrid DNA-nucleobase/peptide-based hydrogels using a multiscale approach based on a large panel of analytical techniques (i.e., rheometry, proton relaxometry, SAXS, electronic microscopy, infrared, circular dichroism, fluorescence, Thioflavin T assays). Among the six multicomponent systems studied, the results highlight the synergistic role of the presence of the two complementary DNA-nucleobases (i.e., adenine/thymine and guanine/cytosine) on the co-assembling process from structural (e.g., morphology of the nanoobjects) to physicochemical (e.g., kinetics of formation, fluorescence properties) and mechanical (e.g., stiffness, resistance to external stress) properties. All the data confirm the relevance of the multicomponent peptide-based approach in the design of innovative hydrogels and bring another brick in the wall of the understanding of these complex and promising systems.

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.

Effect of C12H25O– substituent position on the self-assembly behaviour of C6H5COO–Ala–Ala dipeptide

Intramolecular hydrogen bonding and steric hindrance of side chain lead the different molecular packing of dipeptides and the morphological transformation of self-assemblies’ nanostructures.

Self-Assembled Bio-Organometallic Nanocatalysts for Highly Enantioselective Direct Aldol Reactions

Supramolecular nanocatalysts were designed for asymmetric reactions through the self-assembly process of a bio-organometallic molecule, ferrocene-l-prolinamide (Fc-CO-NH-P). Fc-CO-NH-P could self-assemble into versatile nanostructures in water, including nanospheres, nanosheets, nanoflowers, and pieces. In particular, the self-assembled nanoflowers exhibited a superior specific surface area, high stability, and delicate three-dimensional (3D) chiral catalytic active sites. The nanoflowers could serve as heterogeneous catalysts with an excellent catalytic performance toward direct aldol reactions in aqueous solution, achieving both high yield (>99%) and stereoselectivity (anti/syn = 97:3, ee% >99%). This study proposed a significant strategy to fabricate supramolecular chiral catalysts, serving as a favorable template for designing new asymmetric catalysts.

Recent advances in the fabrication, functionalization, and bioapplications of peptide hydrogels

Self-assembled peptide-based nanomaterials have exhibited wide application potential in the fields of materials science, nanodevices, biomedicine, tissue engineering, biosensors, energy storage, environmental science, and others. Due to their porous structure, strong mechanical stability, high biocompatibility, and easy functionalization, three-dimensional self-assembled peptide hydrogels revealed promising potential in bio-related applications. To present the advances in this interesting topic, we present a review on the synthesis and functionalization of peptide hydrogels, as well as their applications in drug delivery, antibacterial materials, cell culture, biomineralization, bone tissue engineering, and biosensors. Specifically, we focus on the fabrication methods of peptide hydrogels through physical, chemical, and biological stimulations. In addition, the functional design of peptide hydrogels by incorporation with polymers, DNA, protein, nanoparticles, and carbon materials is introduced and discussed in detail. It is expected that this work will be helpful not only for the design and synthesis of various peptide-based nanostructures and nanomaterials, but also for the structural and functional tailoring of peptide-based nanomaterials to meet specific demands.

Aging-Dependent Morphological Crystallinity Determines Membrane Activity of l-Phenylalanine Self-Assembles

Amyloid polymorphism has emerged as an important topic of research in recent years to identify the particular species responsible for several neurodegenerative disorders, whereas the concept is overlooked in the case of the simplest building block, that is, l-phenylalanine (l-Phe) self-assembly. Here, we report the first evidence of l-Phe polymorphism and the conversion of metastable helical fibrillar to thermodynamically stable rodlike crystalline morphologies with increasing time and temperature. Furthermore, only the fibrillar l-Phe polymorph shows a significant modulation of the model membrane. In addition, the l-Phe molecules prefer to arrange in a multilayered rodlike fashion than in a lateral arrangement, which reduces the membrane binding ability of the l-Phe polymorph due to the decrease in the partial charge of the N-terminal of l-Phe units. The present work exemplifies a different approach to understanding l-Phe self-assembly and provides an effective strategy for the therapy of phenylketonuria by scrutinizing the discrete membrane activity of different l-Phe polymorphs.

Improving and fine-tuning the properties of peptide-based hydrogels via incorporation of peptide nucleic acids

Peptide self-assemblies have attracted intense research interest over the last few decades thanks to their implications in key biological processes (e.g., amyloid formation) and their use in biotechnological and (bio)material fields. In particular, peptide-based hydrogels have been highly considered as high potential supramolecular materials in the biomedical domain and open new horizons in terms of applications. To further understand their self-assembly mechanisms and to optimize their properties, several strategies have been proposed with the modification of the constituting amino acid chains via, per se, the introduction of d-amino acids, halogenated amino acids, pseudopeptide bonds, or other chemical moieties. In this context, we report herein on the incorporation of DNA-nucleobases into their peptide nucleic acid (PNA) forms to develop a new series of hybrid nucleopeptides. Thus, depending on the nature of the nucleobase (i.e., thymine, cytosine, adenine or guanine), the physicochemical and mechanical properties of the resulting hydrogels can be significantly improved and fine-tuned with, for instance, drastic enhancements of both the gel stiffness (up to 70-fold) and the gel resistance to external stress (up to 40-fold), and the generation of both thermo-reversible and uncommon red-edge excitation shift (REES) properties. To decipher the actual role of each PNA moiety in the self-assembly processes, the induced modifications from the molecular to the macroscopic scales are studied thanks to the multiscale approach based on a large panel of analytical techniques (i.e., rheology, NMR relaxometry, TEM, thioflavin T assays, FTIR, CD, fluorescence, NMR chemical shift index). Thus, such a strategy provides new opportunities to adapt and fit hydrogel properties to the intended ones and pushes back the limits of supramolecular materials.

Half a century of amyloids: past, present and future

Amyloid diseases are global epidemics with profound health, social and economic implications and yet remain without a cure. This dire situation calls for research into the origin and pathological manifestations of amyloidosis to stimulate continued development of new therapeutics. In basic science and engineering, the cross-β architecture has been a constant thread underlying the structural characteristics of pathological and functional amyloids, and realizing that amyloid structures can be both pathological and functional in nature has fuelled innovations in artificial amyloids, whose use today ranges from water purification to 3D printing. At the conclusion of a half century since Eanes and Glenner's seminal study of amyloids in humans, this review commemorates the occasion by documenting the major milestones in amyloid research to date, from the perspectives of structural biology, biophysics, medicine, microbiology, engineering and nanotechnology. We also discuss new challenges and opportunities to drive this interdisciplinary field moving forward.

Direct Identification of Amyloid Peptide Fragments in Human α-Synuclein Based on Consecutive Hydrophobic Amino Acids

Formation of amyloid fibrils by misfolding α-synuclein is a characteristic feature of Parkinson’s disease, but the exact molecular mechanism of this process has long been an unresolved mystery. Identification of critical amyloid peptide fragments from α-synuclein may hold the key to decipher this mystery. Focusing on consecutive hydrophobic amino acids (CHAA) in the protein sequence, in this study we proposed a sequence-based strategy for direct identification of amyloid peptide fragments in α-synuclein. We picked out three CHAA fragments (two hexapeptides and one tetrapeptide) from α-synuclein and studied their amyloidogenic property. The thioflavin-T binding test, transmission electron microscopy, Congo red staining, and Fourier transform infrared spectroscopy revealed that although only hexapeptides could undergo amyloid aggregation on their own, extended peptide fragments based on any of the three peptides could form typical amyloid fibrils. Primary amyloidogenic fragments based on the three peptides showed synergetic aggregation behavior and could accelerate the aggregation of full-length α-synuclein. It was proved that hydrophobic interaction played a predominant role for the aggregation of these peptides and full-length α-synuclein. A central alanine-to-lysine substitution in each hydrophobic fragment completely eliminated the peptides’ amyloidogenic property, and alanine-to-lysine substitutions at corresponding sites in full-length α-synuclein also decreased the protein’s amyloidogenic potency. These findings suggested that CHAA fragments were potentially amyloidogenic and played an important role for the aggregation of α-synuclein. The identification of these fragments might provide helpful information for eventually clarifying the molecular mechanism of α-synuclein aggregation. On the other hand, our study suggested that the CHAA fragment might be a simple motif for direct sequence-based identification of amyloid peptides.

Nanomechanical Properties and Phase Behavior of Phenylalanine Amyloid Ribbon Assemblies and Amorphous Self-Healing Hydrogels

Phenylalanine was the minimalistic and first of numerous nonproteinaceous building blocks to be demonstrated to form amyloid-like fibrils. This unexpected organization of such a simple building block into canonical architecture, which was previously observed only with proteins and peptides, has numerous implications for medicine and supramolecular chemistry. However, the morphology of phenylalanine fibrils and their mechanical properties was never characterized in solutions. Here, using electron and atomic force microscopy, we analyze the morphological and mechanical properties of phenylalanine fibrils in both air and fluids. The fibrils demonstrate an exceptionally high Young's modulus (up to 30 GPa) and are found to be composed of intertwined protofilaments in a helical or twisted ribbon morphology. In addition, X-ray scattering experiments provide convincing evidence of an amyloidal cross-β-like secondary structure within the nanoassemblies. Furthermore, increasing the phenylalanine concentration results in the formation of highly homogenous, noncrystalline, self-healing hydrogels that display storage and loss moduli significantly higher than similar noncovalently cross-linked biomolecular nanofibrillar scaffolds. These remarkably stiff nanofibrillar hydrogels can be harnessed for various technological and biomedical applications, such as self-healing, printable, structural, load-bearing 3D scaffolds. The properties of this simple but quite remarkable hydrogel open a possibility to utilize it in the biomaterial industry.

Amyloid Evolution: Antiparallel Replaced by Parallel

Several atomic structures have now been found for micrometer-scale amyloid fibrils or elongated microcrystals using a range of methods, including NMR, electron microscopy, and X-ray crystallography, with parallel β-sheet appearing as the most common secondary structure. The etiology of amyloid disease, however, indicates nanometer-scale assemblies of only tens of peptides as significant agents of cytotoxicity and contagion. By combining solution X-ray with molecular dynamics, we show that antiparallel structure dominates at the first stages of aggregation for a specific set of peptides, being replaced by parallel at large length scales only. This divergence in structure between small and large amyloid aggregates should inform future design of molecular therapeutics against nucleation or intercellular transmission of amyloid. Calculations and an overview from the literature argue that antiparallel order should be the first appearance of structure in many or most amyloid aggregation processes, regardless of the endpoint. Exceptions to this finding should exist, depending inevitably on the sequence and on solution conditions.

Kinetic Control of Parallel versus Antiparallel Amyloid Aggregation via Shape of the Growing Aggregate

By combining atomistic and higher-level modelling with solution X-ray diffraction we analyse self-assembly pathways for the IFQINS hexapeptide, a bio-relevant amyloid former derived from human lysozyme. We verify that (at least) two metastable polymorphic structures exist for this system which are substantially different at the atomistic scale, and compare the conditions under which they are kinetically accessible. We further examine the higher-level polymorphism for these systems at the nanometre to micrometre scales, which is manifested in kinetic differences and in shape differences between structures instead of or as well as differences in the small-scale contact topology. Any future design of structure based inhibitors of the IFQINS steric zipper, or of close homologues such as TFQINS which are likely to have similar structures, should take account of this polymorphic assembly.

pH-Controlled Chiral Packing and Self-Assembly of a Coumarin Tetrapeptide

A coumarin-tetrapeptide conjugate, EFEK(DAC)-NH₂ (1), is reported to undergo a pH-dependent interconversion between nanotubes and nanoribbons. An examination of zeta potential measurements, circular dichroism (CD) spectra, and microscopy imaging (transmission electron microscopy and atomic force microscopy) identified three different self-assembly regimes based on pH: (1) pH 2-5, positively charged, left-handed helical nanotubes; (2) pH 6-8, negatively charged, right-handed helical nanoribbons; and (3) pH ≥ 9.0, a monomeric/disassembled peptide. The nanotubes exhibited uniform diameters of 41 ± 5 nm and wall thicknesses of 4.8 ± 0.8 nm, whereas the nanoribbons existed as either flat or twisted sheets ranging in width from 11 to 60 nm with heights of 8 ± 1 nm. The UV-vis and CD spectra of the most common antiparallel, β-sheet conformation of 1-dimer were simulated at the B3LYP/def2svpd level of theory in implicit water. These studies indicated that the transition from nanotubes to nanoribbons was coupled to an M → P helical inversion of the coumarin packing orientation, respectively, within the nanostructures. The assembly process was driven by β-sheet aggregation and π-π interactions, leading to the formation of nanoribbons, which progressively wound into helical ribbons and laterally grew into smooth nanotubes as the pH decreased.

Amyloid-like peptide nanofibrils as scaffolds for tissue engineering: Progress and challenges (Review)

Networks of amyloid-like nanofibrils assembled from short peptide sequences have the ability to form scaffolds that can encapsulate clinically relevant stem cells encouraging their attachment, growth, and differentiation into various lineages which can be used in tissue engineering applications to treat a range of diseases and traumas. In this review, the author highlights a selection of important proof-of-principle papers that show how this class of self-assembled networks is highly suited to biomaterial scaffold development. The author highlights recent studies which have shown that these scaffolds can be used to promote cell and tissue regeneration both in vitro and in vivo. The author also presents some fundamental knowledge gaps which are preventing the widespread translation of such scaffolds. Finally, the author outlines a selection of studies that elucidate molecular assembly mechanisms and biophysical properties of amyloid-like peptide nanofibrils and suggests how studies like these might lead to the ability to generate nanofibril scaffolds with bespoke properties for tissue engineering.

Polyamine-induced, chiral expression from liquid crystalline peptide nanofilaments to long-range ordered nanohelices

We reported the condensation and transformation of peptide micelles into well-defined nanohelices through the incorporation of natural polyamines. The liquid-crystalline peptide micelles are assembled by a short dipeptide amphiphile driven by strong electrostatic repulsions and aromatic stacking attractions. By incorporating polyamines into the peptide solutions, like-charge attractions were achieved to induce the condensation of the like-charged nanofilaments into giant bundles. Intriguingly, by increasing the temperature or electrostatic screening effects, the nanofilaments within the bundles fuse with each other into well-defined flat ribbons which then spontaneously twisted into macroscopically aligned nanohelices. Moreover, the chiral interactions between the aromatic groups of adjacent peptides are inverted from right-handedness to left-handedness during the formation of nanohelices. The results provide new insights into the chiral evolution during peptide self-assembly and offer opportunities for the design of peptide materials with new properties, such as anisotropic hydrogels and long-range ordered chiral nanostructures.

Conditions Governing Food Protein Amyloid Fibril Formation-Part I: Egg and Cereal Proteins

Conditions including heating mode, time, temperature, pH, moisture and protein concentration, shear, and the presence of alcohols, chaotropic/reducing agents, enzymes, and/or salt influence amyloid fibril (AF) formation as they can affect the accessibility of amino acid sequences prone to aggregate. As some conditions applied on model protein resemble conditions in food processing unit operations, we here hypothesize that food processing can lead to formation of protein AFs with a compact cross β-sheet structure. This paper reviews conditions and food constituents that affect amyloid fibrillation of egg and cereal proteins. While egg and cereal proteins often coexist in food products, their impact on each other's fibrillation remains unknown. Hen egg ovalbumin and lysozyme form AFs when subjected to moderate heating at acidic pH separately. AFs can also be formed at higher pH, especially in the presence of alcohols or chaotropic/reducing agents. Tryptic wheat gluten digests can form fibrillar structures at neutral pH and maize and rice proteins do so in aqueous ethanol or at acidic pH, respectively.

Amino acid conformations control the morphological and chiral features of the self-assembled peptide nanostructures: Young investigators perspective

HYPOTHESIS

A variety of nanostructures with different chiral features can be self-assembled from short peptides with highly similar sequences. We hypothesize that these supramolecular nanostructures are ruled by the constituent amino acid residues which adopt their conformations under the influence of intra-/inter-molecular interactions during peptide self-assembly.

APPROACH

Through reviewing recent advances in the self-assembly of short peptides and focusing on the relationship between amino acid conformations, peptide secondary structures and intra-/inter-molecular interactions within the supramolecular architectures, we aim to rationalize the complex interactive processes involved in the self-assembly of short, designed peptides.

RESULTS

Given the highly complexing interactive processes, the adoption of amino acid conformations and their control over peptide self-assembly consist of 4 main steps: (1) Each amino acid residue adopts its unique conformation in a specific sequence; (2) The sequence exhibits its own main chain geometry and determines the propensity of the intermolecular alignment within the building block; (3) The structural propensity of the building block and the packing mode between them determine the self-assembled structural features such as twisting, growth and chirality; (4) In addition to intra-/inter-molecular interactions, inter-sheet and inter-building block interactions could also affect the residue conformations and nanostructures, causing structural readjustment.

Polar-π Interactions Promote Self-assembly of Dipeptides into Laminated Nanofibers

Precise incorporation of functional residues into sequences allows for tailoring the noncovalent interactions between peptides to guide their self-assembly into well-defined nanostructures, thus facilitating creation of artificial functional materials resembling natural systems. Here, we report on the self-assembly of dipeptides consisting of one fluorinated phenylalanine unit (Z residue) and one natural aromatic residue into laminated nanofibers predominately driven by polar-π interactions. On the basis of characterizations using transmission electron microscopy, scanning electron microscopy, atomic force microscopy, circular dichroism, Fourier transform infrared spectroscopy, and thioflavin T binding assay, we found that the face-centered stacking pattern of the dipeptides FZ, ZF, and ZY stabilized by the polar-π interactions and antiparallel β-sheet H-bonding interactions led to lamination of nanofibers and formation of ribbonlike nanostructures. Our findings demonstrate that incorporation of fluorinated aromatic units into short peptides not only promotes of polar-π interactions as alternative self-assembling driving forces but also governs the organizing pattern of peptides, thus benefiting creation of well-defined peptide nanostructures.