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Antibiotic resistance of bacteria is considered one of the most alarming developments in modern medicine. While varied pathways for bacteria acquiring antibiotic resistance have been identified, there still are open questions concerning the mechanisms underlying resistance. Here, we show that alpha phenol-soluble modulins (PSMα’s), functional bacterial amyloids secreted byStaphylococcus aureus, catalyze breakup of β-lactams, a prominent class of antibiotic compounds. Specifically, we show that PSMα2 and, particularly, PSMα3 catalyze hydrolysis of the amide-bond four-member ring of nitrocefin, a widely used β-lactam surrogate. Microscopic and spectroscopic analyses of several PSMα3 variants and correlation with their catalytic activities allowed mapping of the catalytic sites on the amyloid fibrils’ surface, specifically underscoring the key roles of the cross-α fibril organization, and the combined electrostatic and nucleophilic functions of the lysine residue array. This study unveils a previously unknown role of functional bacterial amyloids as catalytic agents for antibiotic compounds, pointing to possible mechanisms for antibiotic resistance of bacteria.ToC Graphical Abstract

Summary Amyloid fibrils are one of the hallmarks of Alzheimer's disease (AD), although a causative link between plaque-forming amyloid fibrils and AD pathology remains to be clarified. This study demonstrates, for the first time for a naturally occurring amyloid, that fibrils comprising the 42-residue amyloid-β peptide (Aβ42) exhibit significant catalytic properties. Aβ42 fibrils catalyzed the hydrolysis of the model ester para-nitrophenyl acetate (pNPA) and of acetylthiocholine, a surrogate for the neurotransmitter acetylcholine. Aβ42 fibrils also catalyzed oxidation of the prominent neurotransmitters dopamine and adrenaline. Importantly, the catalytic activity was specifically manifested by mature Aβ42 fibrils and not the peptide monomers or oligomeric Aβ42, the putative neurotoxic species. Furthermore, maximal catalytic activity was recorded by the full-length Aβ42 fibrils, whereas fibrillar assemblies comprising Aβ42 subdomains were significantly less catalytic. The catalytic activity of Aβ fibrils could exhibit insidious roles in AD pathophysiology.

Glucagon is a prominent peptide hormone, playing central roles in the regulation of glucose blood-level and lipid metabolism. Formation of glucagon amyloid fibrils has been previously reported, although no biological functions of such fibrils are known. Here, we demonstrate that glucagon amyloid fibrils catalyze biologically important reactions, including esterolysis, lipid hydrolysis, and dephosphorylation. In particular, we found that glucagon fibrils catalyze dephosphorylation of adenosine triphosphate (ATP), a core metabolic reaction in cell biology. Comparative analysis of several glucagon variants allowed mapping the catalytic activity to an enzymatic pocket-like triad formed at the glucagon fibril surface, comprising the histidyl-serine domain at the N-terminus of the peptide. This study may point to previously unknown physiological roles and pathological consequences of glucagon fibrillation and supports the hypothesis that catalytic activities of native amyloid fibrils play functional roles in human physiology and disease.

Amyloidoses are a family of diseases characterized by abnormal protein folding that leads to fibril aggregates, amyloids. Extensive research efforts are devoted to developing inhibitors to amyloid aggregates. Here we set to explore functionalized titania (TiO

International audience; Neurofibrillary tangles of the Tau protein and plaques of the amyloid β peptide are hallmarks of Alzheimer's disease (AD), which is characterized by the conversion of monomeric proteins/peptides into misfolded β-sheet rich fibrils. Halting the fibrillation process and disrupting the existing aggregates are key challenges for AD drug development. Previously, we performed in vitro high-throughput screening for the identification of potent inhibitors of Tau aggregation using a proxy model, a highly aggregation-prone hexapeptide fragment 306VQIVYK311 (termed PHF6) derived from Tau. Here we have characterized a hit molecule from that screen as a modulator of Tau aggregation using in vitro, in silico, and in vivo techniques. This molecule, an anthraquinone derivative named Purpurin, inhibited ~ 50% of PHF6 fibrillization in vitro at equimolar concentration and disassembled pre-formed PHF6 fibrils. In silico studies showed that Purpurin interacted with key residues of PHF6, which are responsible for maintaining its β-sheets conformation. Isothermal titration calorimetry and surface plasmon resonance experiments with PHF6 and full-length Tau (FL-Tau), respectively, indicated that Purpurin interacted with PHF6 predominantly via hydrophobic contacts and displayed a dose-dependent complexation with FL-Tau. Purpurin was non-toxic when fed to Drosophila and it significantly ameliorated the AD-related neurotoxic symptoms of transgenic flies expressing WT-FL human Tau (hTau) plausibly by inhibiting Tau accumulation and reducing Tau phosphorylation. Purpurin also reduced hTau accumulation in cell culture overexpressing hTau. Importantly, Purpurin efficiently crossed an in vitro human blood-brain barrier model. Our findings suggest that Purpurin could be a potential lead molecule for AD therapeutics.

Human semen contains various amyloidogenic peptides derived from Prostatic Acid Phosphatase (PAP) and Semenogelin proteins that are capable of enhancing HIV-1 infection when assembled into fibrils. The best characterized among them is a 39 amino acid peptide PAP(248–286), which forms amyloid fibrils termed SEVI (semen-derived enhancer of viral infection) that increase the infectivity of HIV-1 by orders of magnitude. Inhibiting amyloid formation by PAP(248–286) may mitigate the sexual transmission of HIV-1. Several vitamins have been shown to reduce the aggregation of amyloids such as Aβ, α-Synuclein, and Tau, which are associated with neurodegenerative diseases. Since ascorbic acid (AA, vitamin C) is the most abundant vitamin in semen with average concentrations of 0.4 mM, we here examined how AA affects PAP(248–286) aggregation in vitro. Using ThT binding assays, transmission electron microscopy, and circular dichroism spectroscopy, a dual and concentration-dependent behavior of AA in modulating PAP(248–286) fibril formation was observed. We found that low molar ratios of AA:PAP(248–286) promoted whereas high molar ratios inhibited PAP(248–286) fibril formation. Accordingly, PAP(248–286) aggregated in the presence of low amounts of AA enhanced HIV-1 infection, whereas excess amounts of AA during aggregation reduced the infectivity enhancing effect in cell culture. Collectively, this work provides a biophysical insight into the effect of AA, an important seminal component, on SEVI fibrillation which might impact amyloid formation kinetics, thereby modulating the biological activity of semen amyloids., Human semen contains various amyloidogenic peptides derived from Prostatic Acid Phosphatase (PAP) and Semenogelin proteins that are capable of enhancing HIV-1 infection when assembled into fibrils.

The amino acid sequence plays an essential role in amyloid formation. Here, using the central core recognition module of the Aβ peptide and its reverse sequence, we show that although both peptides assemble into β-sheets, their morphologies, kinetics and cell toxicities display marked differences. In addition, the native peptide, but not the reverse one, shows notable affinity towards bilayer lipid model membranes that modulates the aggregation pathways to stabilize the oligomeric intermediate states and function as the toxic agent responsible for neuronal dysfunction.

Glycosylation of amyloidogenic proteins enhances their solubility and reduces propensity for aggregation. We therefore, prepared tryptophan-glucosamine conjugates to modulate aggregation of tau-derived PHF6-peptide. Combined in vitro and in silico approaches indicated that these conjugates inhibited oligomerization and fibril formation of PHF6 and disrupted its preformed fibrils at very low concentration. These effects mainly arise from the glucopyranoside moiety.

Metabolite materials are extremely useful to obtain functional bioinspired assemblies with unique physical properties for various applications in the fields of material science, engineering, and medicine by self-assembly of the simplest biological building blocks. Supramolecular co-assembly has recently emerged as a promising extended approach to further expand the conformational space of metabolite assemblies in terms of structural and functional complexity. Yet, the design of synergistically co-assembled amino acids to produce tailor-made functional architectures is still challenging. Herein, we propose a design rule to predict the supramolecular co-assembly of naturally occurring amino acids based on their interlayer separation distances observed in single crystals. Using diverse experimental techniques, we demonstrate that amino acids with comparable interlayer separation strongly interact and co-assemble to produce structural composites distinctly different from their individual properties. However, such an interaction is hampered in a mixture of differentially layer-separated amino acids, which self-sort to generate individual characteristic structures. This study provides a different paradigm for the modular design of supramolecular assemblies based on amino acids with predictable properties.

PAP248⁻286, a 39 amino acid peptide fragment, derived from the prostatic acid phosphatase secreted in human semen, forms amyloid fibrils and facilitates the attachment of retroviruses to host cells that results in the enhancement of viral infection. Therefore, the inhibition of amyloid formation by PAP248⁻286 (termed PAP f39) may likely reduce HIV transmission in AIDS. In this study, we show that the naphthoquinone tryptophan (NQTrp) hybrid molecule significantly inhibited PAP f39 aggregation in vitro in a dose-dependent manner as observed from the ThT assay, ANS assay, and transmission electron microscopy imaging. We found that even at a sub-molar concentration of 20:1 [PAP f39:NQTrp], NQTrp could reduce >50% amyloid formation. NQTrp inhibition of PAP f39 aggregation resulted in non-toxic intermediate species as determined by the vesicle leakage assay. Isothermal titration calorimetry and molecular docking revealed that the binding of NQTrp and PAP f39 is spontaneous, and NQTrp predominantly interacts with the polar and charged residues of the peptide by forming hydrogen bonds and hydrophobic contacts with a strong binding energy. Collectively, these findings indicate that NQTrp holds significant potential as a small molecule inhibitor of semen amyloids.

Enantiomeric carbon dots (C-dots) synthesized from L-lysine or D-lysine, modulate aggregation and cytotoxicity of amyloid beta-42 (Aβ42), the primary constituent of the amyloid plaques associated with Alzheimer's disease. In particular, L-Lys-C-dots dramatically remodeled Aβ42 secondary structure and fibril morphologies, as well as inhibited Aβ42 cytotoxicity and membrane interactions.

Assembly of fibrillar peptide structures is dependent both upon their intrinsic propensities toward β-structure formation, as well as on structural modulation by external molecular factors. β-sheet structures may either be designed to form useful assemblies or be the undesired consequence of protein denaturation to toxic amyloid structures in several neurodegenerative diseases. Membrane bilayers have been implicated as primary initiators and modulators of amyloid fibrillation and the reasons for this effect are yet to be elucidated. Here, we employed a set of three charged peptides having the tendency to form β-sheet fibrils, to investigate the effect of zwitterionic and negatively charged bilayer vesicles on their assembly structures. Microscopic and spectroscopic experiments revealed intimate relationship between peptide/membrane charges and fibrillation properties. Electrostatic attraction was apparent between oppositely charged peptides and vesicles; however, such interactions did not appear to significantly modulate fibril morphologies of either the net anionic peptide or the cationic one. Yet, a dramatic structural effect was observed when the nominal zwitterionic peptide underwent fibrillation in the presence of negatively charged vesicles. Assemblies of this peptide display a net positive charge, which facilitated the counterionic interactions with the vesicles. Furthermore, these interactions templated a unique twisted fiber morphology demonstrating the dramatic effect membrane-mediated interactions exert on fibril morphologies.