Antibodies towards Tyrosine Amyloid-Like Fibrils Allow Toxicity Modulation and Cellular Imaging of the Assemblies

Amyloid Mimicking Assemblies Formed by Glutamine, Glutamic Acid, and Aspartic Acid

The aggregation of amino acids into amyloid-like structures is a critical phenomenon for understanding the pathophysiology of various diseases, including inborn errors of metabolism (IEMs) associated with amino acid imbalances. Previous studies have primarily focused on self-assembly of aromatic amino acids, leading to a limited understanding of nonaromatic, polar amino acids in this context. To bridge this gap, our study investigates the self-assembly and aggregation behavior of specific nonaromatic charged and uncharged polar amino acids l-glutamine (Gln), l-aspartic acid (Asp), and l-glutamic acid (Glu), which have not been reported widely in the context of amyloid aggregation. Upon aging these amino acids under controlled conditions, we observed the formation of uniform, distinct aggregates, with Gln forming fibrillar gel-like structures and Glu exhibiting fibrous globular morphologies. Computational simulations validated these findings, identifying Gln as the most potent in forming stable aggregates, followed by Glu and Asp. These simulations elucidated the driving forces behind the distinct morphologies and stabilities of the aggregates. Thioflavin T assays were employed to confirm the amyloid-like nature of these aggregates, suggesting their potential cytotoxic impact. To assess toxicity, we performed in vitro studies on neural cell lines and in vivo experiments in Caenorhabditis elegans (C. elegans), which demonstrated measurable cytotoxic effects, corroborated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and heat shock survival assays. Importantly, this study fills a critical gap in our understanding on the role of nonaromatic amino acids in amyloidogenesis and its implications for IEMs. Our findings provide a foundation for future investigations into the mechanisms of diseases associated with amino acid accumulation and offer potential avenues for the development of targeted therapeutic strategies.

Acid-assisted self-assembly of pyrene-capped tyrosine ruptures lysosomes to induce cancer cell apoptosis

Induced lysosomal membrane permeabilization (LMP) by peptide self-assembly has emerged as an effective platform for lysosome-targeted cancer therapy. In this study, we shift this strategical paradigm and present an innovative approach to LMP induction through amino acid-based self-assembly. Pyrene-capped tyrosine (Py-Tyr), as a proof-of-concept molecule, is designed with acidity-responsive self-assembly. Under acidic conditions (pH 4), Py-Tyr is protonated with reduced charge repulsion, and self-assembles into micrometer-scaled aggregates, which exceed the biological size of lysosomes. Cell experiments showed that Py-Tyr specifically accumulates in lysosomes and induces lysosome rupture, leading to the release of cathepsin B into the cytoplasm for subsequent apoptosis activation in cancer cells. This study capitalizes on the concept of amino acid assembly for efficient LMP induction, providing a simple and versatile platform for precise and effective therapeutic interventions in cancer therapy.

Targeting phenylalanine assemblies as a prospective disease-modifying therapy for phenylketonuria

Phenylketonuria is characterized by the accumulation of phenylalanine, resulting in severe cognitive and neurological disorders if not treated by a remarkably strict diet. There are two approved drugs today, yet both provide only a partial solution. We have previously demonstrated the formation of amyloid-like toxic assemblies by aggregation of phenylalanine, suggesting a new therapeutic target to be further pursued. Moreover, we showed that compounds that halt the formation of these assemblies also prevent their resulting toxicity. Here, we performed high-throughput screening, searching for compounds with inhibitory effects on phenylalanine aggregation. Morin hydrate, one of the most promising hits revealed during the screen, was chosen to be tested in vivo using a phenylketonuria mouse model. Morin hydrate significantly improved cognitive and motor function with a reduction in the number of phenylalanine brain deposits. Moreover, while phenylalanine levels remained high, we observed a recovery in dopaminergic, adrenergic, and neuronal markers. To conclude, the ability of Morin hydrate to halt phenylalanine aggregation without reducing phenylalanine levels implies the toxic role of the phenylalanine assemblies in phenylketonuria and opens new avenues for disease-modifying treatment.

Amyloidogenic Propensity of Metabolites in the Uric Acid Pathway and Urea Cycle Critically Impacts the Etiology of Metabolic Disorders

Novel insights into the etiology of metabolic disorders have recently been uncovered through the study of metabolite amyloids. In particular, inborn errors of metabolism (IEMs), including gout, Lesch-Nyhan syndrome (LNS), xanthinuria, citrullinemia, and hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome, are attributed to the dysfunction of the urea cycle and uric acid pathway. In this study, we endeavored to understand and mechanistically characterize the aggregative property exhibited by the principal metabolites of the urea cycle and uric acid pathway, specifically hypoxanthine, xanthine, citrulline, and ornithine. Employing scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM), we studied the aggregation profiles of the metabolites. Insights obtained through molecular dynamics (MD) simulation underscore the vital roles of π-π stacking and hydrogen bonding interactions in the self-assembly process, and thioflavin T (ThT) assays further corroborate the amyloid nature of these metabolites. The in vitro MTT assay revealed the cytotoxic trait of these assemblies, a finding that was substantiated by in vivo assays employing the Caenorhabditis elegans (C. elegans) model, which revealed that the toxic effects were more pronounced and dose-specific in the case of metabolites that had aged via longer preincubation. We hence report a compelling phenomenon wherein these metabolites not only aggregate but transform into a soft, ordered assembly over time, eventually crystallizing upon extended incubation, leading to pathological implications. Our study suggests that the amyloidogenic nature of the involved metabolites could be a common etiological link in IEMs, potentially providing a unified perspective to study their pathophysiology, thus offering exciting insights into the development of targeted interventions for these metabolic disorders.

Anti-amyloid potential of some phytochemicals against Aβ-peptide and α-synuclein, tau, prion, and Huntingtin protein

Some molecules self-assemble to create complex structures through molecular self-assembly. Hydrogel preparation, tissue repair, and therapeutic drug delivery are a few applications of molecular self-assembly. However, the self-assembly of amino acids, peptides, and proteins forms amyloid fibrils, resulting in various disorders, most notably neurodegenerative ailments. Examples include the self-assembly of phenylalanine, which causes phenylketonuria; Aβ, which causes Alzheimer's disease; the tau protein, which causes both Alzheimer's and Parkinson's diseases; and α-synuclein, which causes Parkinson's illness. This review provides information related to phytochemicals of great significance that can prevent the formation of, or destabilize, amino acid, peptide, and protein self-assemblies.

Branched-Chain Amino Acid Assembly into Amyloid-like Fibrils Provides a New Paradigm for Maple Syrup Urine Disease Pathology

Inborn error of metabolism disorders (IEMs) are a family of diseases resulting from single-gene mutations that lead to the accumulation of metabolites that are usually toxic or interfere with normal cell function. The etiological link between metabolic alteration and the symptoms of IEMs is still elusive. Several metabolites, which accumulate in IEMs, were shown to self-assemble to form ordered structures. These structures display the same biophysical, biochemical, and biological characteristics as proteinaceous amyloid fibrils. Here, we have demonstrated, for the first time, the ability of each of the branched-chain amino acids (BCAAs) that accumulate in maple syrup urine disease (MSUD) to self-assemble into amyloid-like fibrils depicted by characteristic morphology, binding to indicative amyloid-specific dyes and dose-dependent cytotoxicity by a late apoptosis mechanism. We could also detect the presence of the assemblies in living cells. In addition, by employing several in vitro techniques, we demonstrated the ability of known polyphenols to inhibit the formation of the BCAA fibrils. Our study implies that BCAAs possess a pathological role in MSUD, extends the paradigm-shifting concept regarding the toxicity of metabolite amyloid-like structures, and suggests new pathological targets that may lead to highly needed novel therapeutic opportunities for this orphan disease.

The Metabolostasis Network and the Cellular Depository of Aggregation-Prone Metabolites

The vital role of metabolites across all branches of life and their involvement in various disorders have been investigated for decades. Many metabolites are poorly soluble in water or in physiological buffers and tend to form supramolecular aggregates. On the other hand, in the cell, they should be preserved in a pool and be readily available for the execution of biochemical functions. We thus propose that a quality-control network, termed "metabolostasis", has evolved to regulate the storage and retrieval of aggregation-prone metabolites. Such a system should control metabolite concentration, subcellular localization, supramolecular arrangement, and interaction in dynamic environments, thus enabling normal cellular physiology, healthy development, and preventing disease onset. The paradigm-shifting concept of metabolostasis calls for a reevaluation of the traditional view of metabolite storage and dynamics in physiology and pathology and proposes unprecedented directions for therapeutic targets under conditions where metabolostasis is imbalanced.

Ab initio study of molecular properties of l-tyrosine

CONTEXT

l-Tyrosine is a naturally occurring agent that acts as a precursor in biosynthesis of monoaminergic neurotransmitters in brain such as dopamine, adrenaline, noradrenaline, and hormones like thyroxine and triiodothyronine. While l-tyrosine in vacuo adopts the canonical aminoacid form with -NH2 and -COOH functional groups, from neutral solutions, is crystallizes in the zwitterionic form possessing -NH3+ and -COO- groups. As l-tyrosine is non-innocent agent with respect to redox processes, redox ability in water expressed by the absolute oxidation and reduction potentials is investigated. The cluster analysis applied to a set of nine related neurotransmitters and trace amines confirms that l-tyrosine is mostly similar to aminoacid forms of phenylalanine, octopamine, and noradrenaline.

METHODS

The energetic data at the Hartree-Fock MO-LCAO-SCF method has been conducted using def2-TZVP basis set, and improved by the many-body perturbation theory using the MP2 correction to the correlation energy. For the aminoacid form and the zwitterionic form of l-tyrosine, a set of molecular descriptors has been evaluated (ionization energy, electron affinity, molecular electronegativity, chemical hardness, electrophilicity index, dipole moment, quadrupole moment, and dipole polarizability). The solvent effect (CPCM) is very expressive to the zwitterionic form and alters the sign of the electron affinity from positive to negative values. In parallel, density-functional theory with B3LYP variant in the same basis set has been employed for full geometry optimization of the neutral and ionized forms of l-tyrosine allowing assessing the adiabatic (a) ionization/affinity processes. The complete vibrational analysis enables evaluating thermodynamic functions such as the inner energy, enthalpy, entropy, Gibbs energy, and consequently the absolute oxidation and reduction potentials. Of applied methods, the most reliable are B3LYP(a) results that account to the correlation energy and the electron and nuclear relaxation during the ionization/affinity processes.

Realization of Amyloid-like Aggregation as a Common Cause for Pathogenesis in Diseases

Amyloids were conventionally referred to as extracellular and intracellular accumulation of Aβ42 peptide, which causes the formation of plaques and neurofibrillary tangles inside the brain leading to the pathogenesis in Alzheimer's disease. Subsequently, amyloid-like deposition was found in the etiology of prion diseases, Parkinson's disease, type II diabetes, and cancer, which was attributed to the aggregation of prion protein, α-Synuclein, islet amyloid polypeptide protein, and p53 protein, respectively. Hence, traditionally amyloids were considered aggregates formed exclusively by proteins or peptides. However, since the last decade, it has been discovered that other metabolites, like single amino acids, nucleobases, lipids, glucose derivatives, etc., have a propensity to form amyloid-like toxic assemblies. Several studies suggest direct implications of these metabolite assemblies in the patho-physiology of various inborn errors of metabolisms like phenylketonuria, tyrosinemia, cystinuria, and Gaucher's disease, to name a few. In this review, we present a comprehensive literature overview that suggests amyloid-like structure formation as a common phenomenon for disease progression and pathogenesis in multiple syndromes. The review is devoted to providing readers with a broad knowledge of the structure, mode of formation, propagation, and transmission of different extracellular amyloids and their implications in the pathogenesis of diseases. We strongly believe a review on this topic is urgently required to create awareness about the understanding of the fundamental molecular mechanism behind the origin of diseases from an amyloid perspective and possibly look for a common therapeutic strategy for the treatment of these maladies by designing generic amyloid inhibitors.

Entropically-Driven Co-assembly of l-Histidine and l-Phenylalanine to Form Supramolecular Materials

Molecular self- and co-assembly allow the formation of diverse and well-defined supramolecular structures with notable physical properties. Among the associating molecules, amino acids are especially attractive due to their inherent biocompatibility and simplicity. The biologically active enantiomer of l-histidine (l-His) plays structural and functional roles in proteins but does not self-assemble to form discrete nanostructures. In order to expand the structural space to include l-His-containing materials, we explored the co-assembly of l-His with all aromatic amino acids, including phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp), all in both enantiomeric forms. In contrast to pristine l-His, the combination of this building block with all aromatic amino acids resulted in distinct morphologies including fibers, rods, and flake-like structures. Electrospray ionization mass spectrometry (ESI-MS) indicated the formation of supramolecular co-assemblies in all six combinations, but time-of-flight secondary-ion mass spectrometry (ToF-SIMS) indicated the best seamless co-assembly occurs between l-His and l-Phe while in the other cases, different degrees of phase separation could be observed. Indeed, isothermal titration calorimetry (ITC) suggested the highest affinity between l-His and l-Phe where the formation of co-assembled structures was driven by entropy. In accordance, among all the combinations, the co-assembly of l-His and l-Phe produced single crystals. The structure revealed the formation of a 3D network with nanocavities stabilized by hydrogen bonding between -N (l-His) and -NH (l-Phe). Taken together, using the co-assembly approach we expanded the field of amino acid nanomaterials and showed the ability to obtain discrete supramolecular nanostructures containing l-His based on its specific interactions with l-Phe.

Metal-Ion-Induced Evolution of Phenylalanine Self-Assembly: Structural Polymorphism of Novel Metastable Intermediates

The self-assembly of aromatic amino acids has been widely studied due to their ability to form well-defined amyloid-like fibrillar structures. Herein, for the first time, we report the existence of different metastable intermediate states of diverse morphologies, for example, droplets, spheres, vesicles, flowers, and toroids, that are sequentially formed in aqueous medium during the self-assembly process of phenylalanine in the presence of different divalent (Zn²⁺, Cd²⁺, and Hg²⁺) and trivalent (Al³⁺, Ga³⁺, and In³⁺) metal ions having low pK_a values. Due to metal ion-amino acid coordination and strong hydrophobic interaction induced by these metal ions, spherical aggregates are obtained at the initial stage of the structural evolution and further transformed into other intermediate states. Our work may facilitate understanding of the role of metal ions in the amino acid self-assembly process and broaden future applications of the obtained nanostructures in drug delivery, tissue engineering, bioimaging, biocatalysis, and other fields.

Effect of Metal Ions on the Intrinsic Blue Fluorescence Property and Morphology of Aromatic Amino Acid Self-Assembly

Metal ions are known to strongly bind with different proteins and peptides, resulting in alteration of their different physicochemical properties. In this work, we investigate the effect of metal ions of different nuclear charges and sizes on the intrinsic blue luminescence of the self-assembled structures formed by aromatic amino acids, namely, phenylalanine and tryptophan, using spectroscopic and imaging techniques. The study reveals that the intrinsic blue fluorescence of amino acid assemblies is influenced by metal ions and the pH of the medium. The metal ions with a higher charge to radius ratio promote clusterization which results in the enhancement of the intrinsic fluorescence, an effect known as "clusteroluminescence" of the amino acids aggregates. The imaging study reveals that metal ions with a higher charge to size ratio inhibit the large fibrillation of aromatic amino acids by promoting the formation of small nonfibrillar aggregates through increased hydrophobicity in the medium. The nanoaggregates are assumed to be responsible for the enhancement in the blue "clusteroluminescence".

Metabolite assemblies: A surprising extension to the amyloid hypothesis

The realization of the ability of metabolites to form self-assembled amyloid-like nanostructures was a surprising phenomenon. This discovery paved the way towards understanding the pathophysiology of the inborn error of metabolism disorders from a new perspective, relating them to amyloid-associated diseases that are characterized by the aggregation of proteins and polypeptides. Hence, a 'generic amyloid hypothesis' can be proposed. This theory implies that the formation of amyloid-like structures is a general phenomenon not limited to proteins and reflects a common etiology for both age-related amyloid-associated diseases and inborn error of metabolism disorders. Here, we present a comprehensive survey of the recent research related to metabolite amyloids including their structure formation through self-association, propagation, interactions, transmission, and their role in metabolic disorders and neurodegenerative diseases and their applications for the fabrication of novel materials which implicate metabolite assemblies as a surprising extension to the amyloid scheme.

Unusual Aggregates Formed by the Self-Assembly of Proline, Hydroxyproline, and Lysine

There is a plethora of significant research that illustrates toxic self-assemblies formed by the aggregation of single amino acids, such as phenylalanine, tyrosine, tryptophan, cysteine, and methionine, and their implication on the etiology of inborn errors of metabolisms (IEMs), such as phenylketonuria, tyrosinemia, hypertryptophanemia, cystinuria, and hypermethioninemia, respectively. Hence, studying the aggregation behavior of single amino acids is very crucial from the chemical neuroscience perspective to understanding the common etiology between single amino acid metabolite disorders and amyloid diseases like Alzheimer's and Parkinson's. Herein we report the aggregation properties of nonaromatic single amino acids l-proline (Pro), l-hydroxyproline (Hyp), and l-lysine hydrochloride (Lys). The morphologies of the self-assembled structures formed by Pro, Hyp, and Lys were extensively studied by various microscopic techniques, and controlled morphological transitions were observed under varied concentrations and aging times. The mechanism of structure formation was deciphered by concentration-dependent ¹H NMR analysis, which revealed the crucial role of hydrogen bonding and hydrophobic interactions in the structure formation of Pro, Hyp, and Lys. MTT assays on neural (SHSY5Y) cell lines revealed that aggregates formed by Pro, Hyp, and Lys reduced cell viability in a dose-dependent manner. These results may have important implications in the understanding of the patho-physiology of disorders such as hyperprolinemia, hyperhydroxyprolinemia, and hyperlysinemia since all these IEMs are associated with severe neurodegenerative symptoms, including intellectual disability, seizures, and psychiatric problems. Our future studies will endeavor to study these biomolecular assemblies in greater detail by immuno-histochemical analysis and advanced biophysical assays.

Chemical Chaperones Modulate the Formation of Metabolite Assemblies

The formation of amyloid-like structures by metabolites is associated with several inborn errors of metabolism (IEMs). These structures display most of the biological, chemical and physical properties of protein amyloids. However, the molecular interactions underlying the assembly remain elusive, and so far, no modulating therapeutic agents are available for clinical use. Chemical chaperones are known to inhibit protein and peptide amyloid formation and stabilize misfolded enzymes. Here, we provide an in-depth characterization of the inhibitory effect of osmolytes and hydrophobic chemical chaperones on metabolite assemblies, thus extending their functional repertoire. We applied a combined in vivo-in vitro-in silico approach and show their ability to inhibit metabolite amyloid-induced toxicity and reduce cellular amyloid content in yeast. We further used various biophysical techniques demonstrating direct inhibition of adenine self-assembly and alteration of fibril morphology by chemical chaperones. Using a scaffold-based approach, we analyzed the physiochemical properties of various dimethyl sulfoxide derivatives and their role in inhibiting metabolite self-assembly. Lastly, we employed whole-atom molecular dynamics simulations to elucidate the role of hydrogen bonds in osmolyte inhibition. Our results imply a dual mode of action of chemical chaperones as IEMs therapeutics, that could be implemented in the rational design of novel lead-like molecules.

ASL expression in ALDH1A1+ neurons in the substantia nigra metabolically contributes to neurodegenerative phenotype

Argininosuccinate lyase (ASL) is essential for the NO-dependent regulation of tyrosine hydroxylase (TH) and thus for catecholamine production. Using a conditional mouse model with loss of ASL in catecholamine neurons, we demonstrate that ASL is expressed in dopaminergic neurons in the substantia nigra pars compacta, including the ALDH1A1⁺ subpopulation that is pivotal for the pathogenesis of Parkinson disease (PD). Neuronal loss of ASL results in catecholamine deficiency, in accumulation and formation of tyrosine aggregates, in elevation of α-synuclein, and phenotypically in motor and cognitive deficits. NO supplementation rescues the formation of aggregates as well as the motor deficiencies. Our data point to a potential metabolic link between accumulations of tyrosine and seeding of pathological aggregates in neurons as initiators for the pathological processes involved in neurodegeneration. Hence, interventions in tyrosine metabolism via regulation of NO levels may be therapeutic beneficial for the treatment of catecholamine-related neurodegenerative disorders.

Chemical Perspective of the Mechanism of Action of Antiamyloidogenic Compounds Using a Minimalistic Peptide as a Reductionist Model

The diphenylalanine (FF) residue which is present at the 19 and 20 positions of the amyloid beta (1-42) (Aβ42) peptide sequence is considered as a reductionist model for studying Aβ42 aggregation. FF self-assembles into well-ordered tubular structures via aromatic π-π stacking. Herein the manuscript, we have presented a chemical perspective on the mechanism of action of antiamyloid compounds by assessing their interaction with FF. Therefore, we first coincubated FF fibers with single amino acids, since they are constituted of different R side chains yet have a common structural unit. This study revealed a crucial role of aromatic rings and functional groups like thiol (-SH) in causing destabilization of FF assembly via their interaction with π-electrons participating in π-π stacking present in FF. We further studied the interaction of different nonsteroidal anti-inflammatory drugs (NSAIDs), other known antiamyloidogenic compounds, and host-guest inclusion compounds like cyclodextrin (CD) to assess their mechanism of action and to decipher the functional moiety present in these compounds which could cause destabilization of π-π stacking. From the coincubation experiments, we could surmise a crucial role of aromatic rings present in these compounds for causing interference in aromatic stacking. We further consolidated our observations through microscopy analysis by various spectroscopic methods such as aggregation-induced emission enhancement (AIEE), fluorescence spectroscopy, solution-state ¹H NMR, FTIR, and circular dichroism. The studies presented in the manuscript thus provide significant insights into the role of functional groups in imparting antiamyloid action and open new avenues for an efficient design of antiamyloid drugs in the future.

Microbial Prions: Dawn of a New Era

Protein misfolding and aggregation are associated with human diseases and aging. However, microorganisms widely exploit the self-propagating properties of misfolded infectious protein particles, prions, as epigenetic information carriers that drive various phenotypic adaptations and encode molecular information. Microbial prion research has faced a paradigm shift in recent years, with breakthroughs that demonstrate the great functional and structural diversity of these agents. Here, we outline unorthodox examples of microbial prions in yeast and other microorganisms, focusing on their noncanonical functions. We discuss novel molecular mechanisms for the inheritance of conformationally-encoded epigenetic information and the evolutionary advantages they confer. Lastly, in light of recent advancements in the field of molecular self-assembly, we present a hypothesis regarding the existence of non-proteinaceous prion-like entities.

Laccase-catalyzed cross-linking of BSA mediated by tyrosine

Tyrosine was explored as a cross-linking agent to form cross-linked bovine serum albumin (BSA) using laccase as a catalyst. Liquid chromatography-mass spectrometry (LC-MS) and fluorescence spectra indicated that tyrosine can be mainly oxidized to be dityrosine. Spectra analysis and molecular weight were used to characterize the BSA treated with tyrosine and laccase. Both SDS-PAGE and size exclusion chromatography confirmed the formation of cross-linked BSA, while most of the protein products existed as BSA-tyrosine conjugates. The MALDI-TOF analysis revealed that five tyrosine units were grafted on one BSA monomer, however one cross-linked BSA consists of two BSA monomers and 18 tyrosine. Furthermore, the content of the amino acid of BSA was identified using amino acid analysis, among those the percentage of lysine presented a visible decline from 12.36% to 11.43%, corresponding to 4-5 lysine residues. The pure and modified BSA were hydrolyzed by trypsin and the corresponding peptides were obtained. Different mass of five peptides from LC-MS spectra after hydrolysis indicated that tyrosine could react with Lys-136, Lys-204, Lys-224, Lys-322 and Lys-537 in BSA, promoting the formation of BSA-tyrosine conjugates and cross-linked BSA.

Two Decades of Studying Functional Amyloids in Microorganisms

In the past two decades, amyloids, typically associated with human diseases, have been described to play various functional roles in nearly all life forms. The structural and functional diversity of microbial 'functional amyloids' has dramatically increased in recent years, expanding the canonical definition of these assembled molecules. Here, we provide a broad review of the current understanding of microbial functional amyloids and their diverse roles, putting the spotlight on recent discoveries in the field. We discuss their functions as structural scaffolds, surface-tension modulators, adhesion molecules, cell-cycle and gametogenesis regulators, toxins, and mediators of host-pathogen interactions. We outline how noncanonical amyloid morphologies and sophisticated regulatory mechanisms underlie their functional diversity and emphasize their therapeutic and biotechnological implications and applications.

Induction of retinopathy by fibrillar oxalate assemblies

The formation of metabolite fibrillar assemblies represents a paradigm shift in the study of human metabolic disorders. Yet, direct clinical relevance has been attributed only to metabolite crystals. A notable example for metabolite crystallization is calcium oxalate crystals observed in various diseases, including primary hyperoxaluria. We unexpectedly observed retinal damage among young hyperoxaluria patients in the absence of crystals. Exploring the possible formation of alternative supramolecular organizations and their biological role, here we show that oxalate can form ordered fibrils with no associated calcium. These fibrils inflict intense retinal cytotoxicity in cultured cells. A rat model injected with oxalate fibrils recaptures patterns of retinal dysfunction observed in patients. Antibodies purified from hyperoxaluria patient sera recognize oxalate fibrils regardless of the presence of calcium. These findings highlight a new molecular basis for oxalate-associated disease, and to our knowledge provide the first direct clinical indication for the pathogenic role of metabolite fibrillar assemblies.

C, Koshti B, Kshtriya V, Shah D, Patel S, Agrawal-Rajput R, Pandey MK. Amyloid-like Structures Formed by Single Amino Acid Self-Assemblies of Cysteine and Methionine

We report for the very first time the discovery of amyloid-like self-assemblies formed by the nonaromatic single amino acids cysteine (Cys) and methionine (Met) under neutral aqueous conditions. The structure formation was assessed and characterized by various microscopic and spectroscopic techniques such as optical microscopy, phase contrast microscopy, scanning electron microscopy, and transmission electron microscopy. The mechanism of self-assembly and the role of hydrogen bonding and thiol interactions of Cys and Met were assessed by Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and solid state NMR along with various control experiments. In addition, molecular dynamics simulations were carried out to gain insight into assembly initiation. Further, Thioflavin T and Congo red binding assays with Cys and Met structures indicated that these single amino acid assemblies may have amyloid-like characteristics. To understand the biological significance of the Cys and Met structures, cytotoxicity assays of the assemblies were performed on human neuroblastoma IMR-32 cells and monkey kidney cells (COS-7). The results revealed that both Cys and Met fibers were cytotoxic. The cell viability assay further supported the hypothesis that aggregation of single amino acid may contribute to the etiology of metabolic disorders like cystinuria and hypermethioninemia. The results presented in this study are striking, and to the best of our knowledge this is the first report which demonstrates that nonaromatic amino acids like Cys and Met can undergo spontaneous self-assembly to form amyloidogenic aggregates. The results presented are also consistent with the established generic amyloid hypothesis and support a new paradigm for the study of the etiology of single amino acid initiated metabolic disorders in amyloid related diseases.

Novel model of secreted human tau protein reveals the impact of the abnormal N-glycosylation of tau on its aggregation propensity

Alzheimer’s disease (AD) is the most common neurodegenerative disorder and has no disease-modifying treatment yet. The hallmarks of AD are two amyloidogenic proteins: tau and amyloid β (Aβ). Tau undergoes several posttranslational modifications, including N-glycosylation. Tau was reported to be N-glycosylated in AD brains, but not in healthy counterparts, which may affect AD etiology. Here, we aimed to examine the effect of N-glycosylation on aggregation propensity of tau. To that end, a novel SH-SY5Y cell-based model was generated in which recombinant human tau (htau) is forced to be secreted from the cells. Secreted htau was found to localize in the secretory pathway compartments and to undergo N-glycosylation. Following N-glycan cleavage of the secreted htau, various biophysical results collectively indicated that the untreated N-glycosylated secreted htau is markedly less aggregative, contains thinner and shorter fibrils, as compared to treated de-glycosylated secreted htau. This finding shows that N-glycans attached to htau may affect its aggregation. This could help to better understand the effect of N-glycosylated htau on AD progression.

Fibril formation and therapeutic targeting of amyloid-like structures in a yeast model of adenine accumulation

The extension of the amyloid hypothesis to include non-protein metabolite assemblies invokes a paradigm for the pathology of inborn error of metabolism disorders. However, a direct demonstration of the assembly of metabolite amyloid-like structures has so far been provided only in vitro. Here, we established an in vivo model of adenine self-assembly in yeast, in which toxicity is associated with intracellular accumulation of the metabolite. Using a strain blocked in the enzymatic pathway downstream to adenine, we observed a non-linear dose-dependent growth inhibition. Both the staining with an indicative amyloid dye and anti-adenine assemblies antibodies demonstrated the accumulation of adenine amyloid-like structures, which were eliminated by lowering the supplied adenine levels. Treatment with a polyphenol inhibitor reduced the occurrence of amyloid-like structures while not affecting the dramatic increase in intracellular adenine concentration, resulting in inhibition of cytotoxicity, further supporting the notion that toxicity is triggered by adenine assemblies.

Small molecule metabolites like phenylalanine can form amyloid-like structures but so far this has only been demonstrated in vitro. Here the authors generate a yeast in vivo model of adenine self-assembly and characterize the adenine assemblies in cells by indicative amyloid dye and anti-adenine assemblies antibodies.