Harnessing prion-inspired amyloid self-assembly for sustainable and biocompatible proton conductivity.

Protein-based materials have emerged as promising candidates for proton-conducting biomaterials. Therefore, drawing inspiration from the amino acid composition of prion-like domains, we designed short self-assembling peptides incorporating the (X-Tyr) motif, with X representing Asn, Gly and Ser, which form fibrillar structures capable of conducting protons. In this study, we conducted an analysis of the conductivity capacity of these fibers, with a focus on temperature and frequency dependence of conductivity. The loss tangent curves data and the electrode polarization model with the Debye approximation were employed to calculate transport properties, including conductivity, diffusivity, and density of charge carriers. Results revealed the prion-like fibers can transport protons more efficiently than biomaterials and other synthetic proton conducting materials, and that a significant increase in conductivity is observed with fibrillar orientations. The temperature dependence of conductivity of the peptides, measured in wet conditions, showed conductivities following the trend σ(NY7) < σ(GY7) < σ(SY7), in all the range of temperatures studied. The Arrhenius behavior, and the activation energy associated with conductivity followed the trend: Eact (SY7) = 8.2 ± 0.6 kJ mol-1 < Eact (GY7) < 13 ± 5 kJ mol-1 < Eact (NY7) = 31 ± 7 kJ mol-1, in different range of temperatures depending of the peptide. Furthermore, the diffusion coefficient correlated with increasing temperature in GY7 and SY7 fibers for temperatures compress between 20 °C and 80 °C, while NY7 only below 60 °C. However, it is noteworthy that the diffusivity observed in the SY7 peptide is lower, compared to GY7 and NY7 presumably due to its enlarged length. This observation can be attributed to two factors: firstly, the higher conductivity values observed in SY7 compared to GY7 and NY7, and secondly, to the value of relation observed of cations present in the peptide SY7 compared with GY7 and NY7, which in turn is dependent on temperature. In light of these findings, we envision our prion-inspired nanofibers as highly efficient proton-conducting natural biopolymers that are both biocompatible and biodegradable. These properties provide the opportunity for the development of next-generation bioelectrical interfaces and protonic devices.

Gut microbiota produces biofilm-associated amyloids with potential for neurodegeneration.

Age-related neurodegenerative diseases involving amyloid aggregation remain one of the biggest challenges of modern medicine. Alterations in the gastrointestinal microbiome play an active role in the aetiology of neurological disorders. Here, we dissect the amyloidogenic properties of biofilm-associated proteins (BAPs) of the gut microbiota and their implications for synucleinopathies. We demonstrate that BAPs are naturally assembled as amyloid-like fibrils in insoluble fractions isolated from the human gut microbiota. We show that BAP genes are part of the accessory genomes, revealing microbiome variability. Remarkably, the abundance of certain BAP genes in the gut microbiome is correlated with Parkinson's disease (PD) incidence. Using cultured dopaminergic neurons and Caenorhabditis elegans models, we report that BAP-derived amyloids induce α-synuclein aggregation. Our results show that the chaperone-mediated autophagy is compromised by BAP amyloids. Indeed, inoculation of BAP fibrils into the brains of wild-type mice promote key pathological features of PD. Therefore, our findings establish the use of BAP amyloids as potential targets and biomarkers of α-synucleinopathies.

PITB: A high affinity transthyretin aggregation inhibitor with optimal pharmacokinetic properties.

The aggregation of wild-type transthyretin (TTR) and over 130 genetic TTR variants underlies a group of lethal disorders named TTR amyloidosis (ATTR). TTR chemical chaperones are molecules that hold great promise to modify the course of ATTR progression. In previous studies, we combined rational design and molecular dynamics simulations to generate a series of TTR selective kinetic stabilizers displaying exceptionally high affinities. In an effort to endorse the previously developed molecules with optimal pharmacokinetic properties, we conducted structural design optimization, leading to the development of PITB. PITB binds with high affinity to TTR, effectively inhibiting tetramer dissociation and aggregation of both the wild-type protein and the two most prevalent disease-associated TTR variants. Importantly, PITB selectively binds and stabilizes TTR in plasma, outperforming tolcapone, a drug currently undergoing clinical trials for ATTR. Pharmacokinetic studies conducted on mice confirmed that PITB exhibits encouraging pharmacokinetic properties, as originally intended. Furthermore, PITB demonstrates excellent oral bioavailability and lack of toxicity. These combined attributes position PITB as a lead compound for future clinical trials as a disease-modifying therapy for ATTR.

Amyloid Fibrils Formed by Short Prion-Inspired Peptides Are Metalloenzymes.

Enzymes typically fold into defined 3D protein structures exhibiting a high catalytic efficiency and selectivity. It has been proposed that the earliest enzymes may have arisen from the self-assembly of short peptides into supramolecular amyloid-like structures. Several artificial amyloids have been shown to display catalytic activity while offering advantages over natural enzymes in terms of modularity, flexibility, stability, and reusability. Hydrolases, especially esterases, are the most common artificial amyloid-like nanozymes with some reported to act as carbonic anhydrases (CA). Their hydrolytic activity is often dependent on the binding of metallic cofactors through a coordination triad composed of His residues in the ß-strands, which mimic the arrangement found in natural metalloenzymes. Tyr residues contribute to the coordination of metal ions in the active center of metalloproteins; however, their use has been mostly neglected in the design of metal-containing amyloid-based nanozymes. We recently reported that four different polar prion-inspired heptapeptides spontaneously self-assembled into amyloid fibrils. Their sequences lack His but contain three alternate Tyr residues exposed to solvent. We combine experiments and simulations to demonstrate that the amyloid fibrils formed by these peptides can efficiently coordinate and retain different divalent metal cations, functioning as both metal scavengers and nanozymes. The metallized fibrils exhibit esterase and CA activities without the need for a histidine triad. These findings highlight the functional versatility of prion-inspired peptide assemblies and provide a new sequential context for the creation of artificial metalloenzymes. Furthermore, our data support amyloid-like structures acting as ancestral catalysts at the origin of life.

OligoBinders: Bioengineered Soluble Amyloid-like Nanoparticles to Bind and Neutralize SARS-CoV-2.

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has become a primary health concern. Molecules that prevent viral entry into host cells by interfering with the interaction between SARS-CoV-2 spike (S) protein and the human angiotensin-converting enzyme 2 receptor (ACE2r) opened a promising avenue for virus neutralization. Here, we aimed to create a novel kind of nanoparticle that can neutralize SARS-CoV-2. To this purpose, we exploited a modular self-assembly strategy to engineer OligoBinders, soluble oligomeric nanoparticles decorated with two miniproteins previously described to bind to the S protein receptor binding domain (RBD) with high affinity. The multivalent nanostructures compete with the RBD-ACE2r interaction and neutralize SARS-CoV-2 virus-like particles (SC2-VLPs) with IC50 values in the pM range, preventing SC2-VLPs fusion with the membrane of ACE2r-expressing cells. Moreover, OligoBinders are biocompatible and significantly stable in plasma. Overall, we describe a novel protein-based nanotechnology that might find application in SARS-CoV-2 therapeutics and diagnostics.

Development of a Highly Potent Transthyretin Amyloidogenesis Inhibitor: Design, Synthesis, and Evaluation.

Transthyretin amyloidosis (ATTR) is a group of fatal diseases described by the misfolding and amyloid deposition of transthyretin (TTR). Discovering small molecules that bind and stabilize the TTR tetramer, preventing its dissociation and subsequent aggregation, is a therapeutic strategy for these pathologies. Departing from the crystal structure of TTR in complex with tolcapone, a potent binder in clinical trials for ATTR, we combined rational design and molecular dynamics (MD) simulations to generate a series of novel halogenated kinetic stabilizers. Among them, M-23 displays one of the highest affinities for TTR described so far. The TTR/M-23 crystal structure confirmed the formation of unprecedented protein-ligand contacts, as predicted by MD simulations, leading to an enhanced tetramer stability both in vitro and in whole serum. We demonstrate that MD-assisted design of TTR ligands constitutes a new avenue for discovering molecules that, like M-23, hold the potential to become highly potent drugs to treat ATTR.

Computational methods to predict protein aggregation.

In most cases, protein aggregation stems from the establishment of non-native intermolecular contacts. The formation of insoluble protein aggregates is associated with many human diseases and is a major bottleneck for the industrial production of protein-based therapeutics. Strikingly, fibrillar aggregates are naturally exploited for structural scaffolding or to generate molecular switches and can be artificially engineered to build up multi-functional nanomaterials. Thus, there is a high interest in rationalizing and forecasting protein aggregation. Here, we review the available computational toolbox to predict protein aggregation propensities, identify sequential or structural aggregation-prone regions, evaluate the impact of mutations on aggregation or recognize prion-like domains. We discuss the strengths and limitations of these algorithms and how they can evolve in the next future.

Design, synthesis and structure-activity evaluation of novel 2-pyridone-based inhibitors of α-synuclein aggregation with potentially improved BBB permeability.

The treatment of Parkinson's disease (PD), the second most common neurodegenerative human disorder, continues to be symptomatic. Development of drugs able to stop or at least slowdown PD progression would benefit several million people worldwide. SynuClean-D is a low molecular weight 2-pyridone-based promising drug candidate that inhibits the aggregation of α-synuclein in human cultured cells and prevents degeneration of dopaminergic neurons in a Caenorhabditis elegans model of PD. Improving SynuClean-D pharmacokinetic/pharmacodynamic properties, performing structure/activity studies and testing its efficacy in mammalian models of PD requires the use of gr-amounts of the compound. However, not enough compound is on sale, and no synthetic route has been reported until now, which hampers the molecule progress towards clinical trials. To circumvent those problems, we describe here an efficient and economical route that enables the synthesis of SynuClean-D with good yields as well as the synthesis of SynuClean-D derivatives. Structure-activity comparison of the new compounds with SynuClean-D reveals the functional groups of the molecule that can be disposed of without activity loss and those that are crucial to interfere with α-synuclein aggregation. Several of the derivatives obtained retain the parent's compound excellent in vitro anti-aggregative activity, without compromising its low toxicity. Computational predictions and preliminary testing indicate that the blood brain barrier (BBB) permeability of SynuClean-D is low. Importantly, several of the newly designed and obtained active derivatives are predicted to display good BBB permeability. The synthetic route developed here will facilitate their synthesis for BBB permeability determination and for efficacy testing in mammalian models of PD.

Functionalized Prion-Inspired Amyloids for Biosensor Applications.

Protein amyloid nanofibers provide a biocompatible platform for the development of functional nanomaterials. However, the functionalities generated up to date are still limited. Typical building blocks correspond to aggregation-prone proteins and peptides, which must be modified by complex and expensive reactions post-assembly. There is high interest in researching alternative strategies to tailor amyloid-based nanostructures' functionality on demand. In the present study, the biotin-streptavidin system was exploited for this purpose. Prion-inspired heptapeptides (Ac-NYNYNYN-NH2, Ac-QYQYQYQ-NH2, and Ac-SYSYSYS-NH2) were doped with biotin-conjugated counterparts and assembled into amyloid-like fibers under mild conditions. The scaffolds' versatile functionalization was demonstrated by decorating them with different streptavidin conjugates, including gold nanoparticles, quantum dots, and enzymes. In particular, they were functionalized with peroxidase or phosphatase activities using streptavidin conjugated with horseradish peroxidase and alkaline phosphatase, respectively. Modification of amyloid-like nanostructures has generally been restricted to the addition of a single protein moiety. We functionalized the fibrils simultaneously with glucose oxidase and horseradish peroxidase, coupling these activities to build up a nanostructured glucose biosensor. Overall, we present a simple, modular, and multivalent approach for developing amyloid-based nanomaterials functionalized with any desired combination of chemical and biological moieties.

α-Helical peptidic scaffolds to target α-synuclein toxic species with nanomolar affinity.

α-Synuclein aggregation is a key driver of neurodegeneration in Parkinson's disease and related syndromes. Accordingly, obtaining a molecule that targets α-synuclein toxic assemblies with high affinity is a long-pursued objective. Here, we exploit the biophysical properties of toxic oligomers and amyloid fibrils to identify a family of α-helical peptides that bind to these α-synuclein species with low nanomolar affinity, without interfering with the monomeric functional protein. This activity is translated into a high anti-aggregation potency and the ability to abrogate oligomer-induced cell damage. Using a structure-guided search we identify a human peptide expressed in the brain and the gastrointestinal tract with analogous binding, anti-aggregation, and detoxifying properties. The chemical entities we describe here may represent a therapeutic avenue for the synucleinopathies and are promising tools to assist diagnosis by discriminating between native and toxic α-synuclein species.

MIRRAGGE - Minimum Information Required for Reproducible AGGregation Experiments.

Reports on phase separation and amyloid formation for multiple proteins and aggregation-prone peptides are recurrently used to explore the molecular mechanisms associated with several human diseases. The information conveyed by these reports can be used directly in translational investigation, e.g., for the design of better drug screening strategies, or be compiled in databases for benchmarking novel aggregation-predicting algorithms. Given that minute protocol variations determine different outcomes of protein aggregation assays, there is a strong urge for standardized descriptions of the different types of aggregates and the detailed methods used in their production. In an attempt to address this need, we assembled the Minimum Information Required for Reproducible Aggregation Experiments (MIRRAGGE) guidelines, considering first-principles and the established literature on protein self-assembly and aggregation. This consensus information aims to cover the major and subtle determinants of experimental reproducibility while avoiding excessive technical details that are of limited practical interest for non-specialized users. The MIRRAGGE table (template available in Supplementary Information) is useful as a guide for the design of new studies and as a checklist during submission of experimental reports for publication. Full disclosure of relevant information also enables other researchers to reproduce results correctly and facilitates systematic data deposition into curated databases.

Inhibition of α-Synuclein Aggregation and Mature Fibril Disassembling With a Minimalistic Compound, ZPDm.

Synucleinopathies are a group of disorders characterized by the accumulation of α-Synuclein amyloid inclusions in the brain. Preventing α-Synuclein aggregation is challenging because of the disordered nature of the protein and the stochastic nature of fibrillogenesis, but, at the same time, it is a promising approach for therapeutic intervention in these pathologies. A high-throughput screening initiative allowed us to discover ZPDm, the smallest active molecule in a library of more than 14.000 compounds. Although the ZPDm structure is highly related to that of the previously described ZPD-2 aggregation inhibitor, we show here that their mechanisms of action are entirely different. ZPDm inhibits the aggregation of wild-type, A30P, and H50Q α-Synuclein variants in vitro and interferes with α-Synuclein seeded aggregation in protein misfolding cyclic amplification assays. However, ZPDm distinctive feature is its strong potency to dismantle preformed α-Synuclein amyloid fibrils. Studies in a Caenorhabditis elegans model of Parkinson's Disease, prove that these in vitro properties are translated into a significant reduction in the accumulation of α-Synuclein inclusions in ZPDm treated animals. Together with previous data, the present work illustrates how different chemical groups on top of a common molecular scaffold can result in divergent but complementary anti-amyloid activities.

Coiled-coil inspired functional inclusion bodies.

BACKGROUND: Recombinant protein expression in bacteria often leads to the formation of intracellular insoluble protein deposits, a major bottleneck for the production of soluble and active products. However, in recent years, these bacterial protein aggregates, commonly known as inclusion bodies (IBs), have been shown to be a source of stable and active protein for biotechnological and biomedical applications. The formation of these functional IBs is usually facilitated by the fusion of aggregation-prone peptides or proteins to the protein of interest, leading to the formation of amyloid-like nanostructures, where the functional protein is embedded. RESULTS: In order to offer an alternative to the classical amyloid-like IBs, here we develop functional IBs exploiting the coiled-coil fold. An in silico analysis of coiled-coil and aggregation propensities, net charge, and hydropathicity of different potential tags identified the natural homo-dimeric and anti-parallel coiled-coil ZapB bacterial protein as an optimal candidate to form assemblies in which the native state of the fused protein is preserved. The protein itself forms supramolecular fibrillar networks exhibiting only α-helix secondary structure. This non-amyloid self-assembly propensity allows generating innocuous IBs in which the recombinant protein of interest remains folded and functional, as demonstrated using two different fluorescent proteins. CONCLUSIONS: Here, we present a proof of concept for the use of a natural coiled-coil domain as a versatile tool for the production of functional IBs in bacteria. This α-helix-based strategy excludes any potential toxicity drawback that might arise from the amyloid nature of ß-sheet-based IBs and renders highly active and homogeneous submicrometric particles.

Soluble Assemblies in the Fibrillation Pathway of Prion-Inspired Artificial Functional Amyloids are Highly Cytotoxic.

Amyloids are associated with human disease. However, they are also exploited by nature for functional purposes. Functional amyloids have inspired amyloid-based biomaterials for different nanotechnologies. Early soluble species in the fibrillation pathway seem to be the primary elicitors of cytotoxicity, instead of fibrils. Organisms have evolved dedicated mechanisms to avoid toxicity during the assembly of functional amyloids. In their absence, artificial amyloid-based nanomaterials might also produce toxic intermediates. We show here that even when the building blocks of artificial amyloids are small, polar, and compositionally simple, their early soluble assemblies are extremely cytotoxic, causing cell death through mechanisms identical to those of disease-associated proteins. Our results raise safety concerns about the use of non-natural amyloid-based materials without a rigorous characterization of their fibrillation pathway. Besides, the simple, cheap, and easy to synthesize peptides we use here might turn very useful to understand the molecular determinants behind amyloid cytotoxicity.

The biofilm-associated surface protein Esp of Enterococcus faecalis forms amyloid-like fibers.

Functional amyloids are considered as common building block structures of the biofilm matrix in different bacteria. In previous work, we have shown that the staphylococcal surface protein Bap, a member of the Biofilm-Associated Proteins (BAP) family, is processed and the fragments containing the N-terminal region become aggregation-prone and self-assemble into amyloid-like structures. Here, we report that Esp, a Bap-orthologous protein produced by Enterococcus faecalis, displays a similar amyloidogenic behavior. We demonstrate that at acidic pH the N-terminal region of Esp forms aggregates with an amyloid-like conformation, as evidenced by biophysical analysis and the binding of protein aggregates to amyloid-indicative dyes. Expression of a chimeric protein, with its Esp N-terminal domain anchored to the cell wall through the R domain of clumping factor A, showed that the Esp N-terminal region is sufficient to confer multicellular behavior through the formation of an extracellular amyloid-like material. These results suggest that the mechanism of amyloid-like aggregation to build the biofilm matrix might be widespread among BAP-like proteins. This amyloid-based mechanism may not only have strong relevance for bacteria lifestyle but could also contribute to the amyloid burden to which the human physiology is potentially exposed.

Atomistic fibrillar architectures of polar prion-inspired heptapeptides.

This article provides the computational prediction of the atomistic architectures resulting from self-assembly of the polar heptapeptide sequences NYNYNYN, SYSYSYS and GYGYGYG. Using a combination of molecular dynamics and a newly developed tool for non-covalent interaction analysis, we uncover the properties of a new class of bionanomaterials, including hydrogen-bonded polar zippers, and the relationship between peptide composition, fibril geometry and weak interaction networks. Our results, corroborated by experimental observations, provide the basis for the rational design of prion-inspired nanomaterials.

Computational re-design of protein structures to improve solubility.

Introduction: The rapid development of protein therapeutics is providing life-saving therapies for a wide range of human diseases. However, degradation reactions limit the quality and performance of these protein-based drugs. Among them, protein aggregation is the most common and one of the most challenging to prevent. Aggregation impacts biopharmaceutical development at every stage, from discovery to production and storage. In addition, regulators are highly concerned about the impact of protein aggregates on drug product safety. Area covered: Herein, the authors review existing protein aggregation prediction approaches, with a special focus on four recently developed algorithms aimed to predict and improve solubility using three-dimensional protein coordinates: SAP, CamSol, Solubis and Aggrescan3D. Furthermore, they illustrate their potential to assist the design of solubility-improved proteins with a number of examples. Expert opinion: Aggregation of protein-based drugs is, traditionally, addressed via wet lab experiments, using trial and error approaches that are expensive, difficult to perform and time-consuming. The structure-based in silico methods we describe here can predict accurately aggregation propensities, allowing researchers to work with pre-selected, well-behaved, protein candidates. These methods should contribute to the reduction of the time to the marketplace along with industrial costs and improve the safety of future therapeutic proteins.

Prion soft amyloid core driven self-assembly of globular proteins into bioactive nanofibrils.

Amyloids have been exploited to build amazing bioactive materials. In most cases, short synthetic peptides constitute the functional components of such materials. The controlled assembly of globular proteins into active amyloid nanofibrils is still challenging, because the formation of amyloids implies a conformational conversion towards a ß-sheet-rich structure, with a concomitant loss of the native fold and the inactivation of the protein. There is, however, a remarkable exception to this rule: yeast prions. They are singular proteins able to switch between a soluble and an amyloid state. In both states, the structure of their globular domains remains essentially intact. The transit between these two conformations is encoded in prion domains (PrDs): long and disordered sequences to which the active globular domains are appended. PrDs are much larger than typical self-assembling peptides. This seriously limits their use for nanotechnological applications. We have recently shown that these domains contain soft amyloid cores (SACs) that suffice to nucleate their self-assembly reaction. Here we genetically fused a model SAC with different globular proteins. We demonstrate that this very short sequence acts as a minimalist PrD, driving the selective and slow assembly of the initially soluble fusion proteins into amyloid fibrils in which the globular proteins retain their native structure and display high activity. Overall, we provide here a novel, modular and straightforward strategy to build active protein-based nanomaterials at a preparative scale.

Biasing the native α-synuclein conformational ensemble towards compact states abolishes aggregation and neurotoxicity.

The aggregation of α-synuclein (α-syn) into amyloid fibrils is a major pathological hallmark of Parkinson's disease (PD) and other synucleinopathies. The mechanisms underlying the structural transition of soluble and innocuous α-syn to aggregated neurotoxic forms remains largely unknown. The disordered nature of α-syn has hampered the use of structure-based protein engineering approaches to elucidate the molecular determinants of this transition. The recent 3D structure of a pathogenic α-syn fibril provides a template for this kind of studies. The structure supports the NAC domain being a critical element in fibril formation, since it constitutes the core of the fibril, delineating a Greek-key motif. Here, we stapled the ends of this motif with a designed disulfide bond and evaluated its impact on the conformation, aggregation and toxicity of α-syn in different environments. The new covalent link biases the native structural ensemble of α-syn toward compact conformations, reducing the population of fully unfolded species. This conformational bias results in a strongly reduced fibril formation propensity both in the absence and in the presence of lipids and impedes the formation of neurotoxic oligomers. Our study does not support the Greek-key motif being already imprinted in early α-syn assemblies, discarding it as a druggable interface to prevent the initiation of fibrillation. In contrast, it suggests the stabilization of native, compact ensembles as a potential therapeutic strategy to avoid the formation of toxic species and to target the early stages of PD.

ZPD-2, a Small Compound That Inhibits α-Synuclein Amyloid Aggregation and Its Seeded Polymerization.

α-Synuclein (α-Syn) forms toxic intracellular protein inclusions and transmissible amyloid structures in Parkinson's disease (PD). Preventing α-Syn self-assembly has become one of the most promising approaches in the search for disease-modifying treatments for this neurodegenerative disorder. Here, we describe the capacity of a small molecule (ZPD-2), identified after a high-throughput screening, to inhibit α-Syn aggregation. ZPD-2 inhibits the aggregation of wild-type α-Syn and the A30P and H50Q familial variants in vitro at substoichiometric compound:protein ratios. In addition, the molecule prevents the spreading of α-Syn seeds in protein misfolding cyclic amplification assays. ZPD-2 is active against different α-Syn strains and blocks their seeded polymerization. Treating with ZPD-2 two different PD Caenorhabditis elegans models that express α-Syn either in muscle or in dopaminergic (DA) neurons substantially reduces the number of α-Syn inclusions and decreases synuclein-induced DA neurons degeneration. Overall, ZPD-2 is a hit compound worth to be explored in order to develop lead molecules for therapeutic intervention in PD.