Analysis of core region from egg white lysozyme forming amyloid fibrils

Ankaflavin and Monascin Prevent Fibrillogenesis of Hen Egg White Lysozyme: Focus on Noncovalent and Covalent Interactions

Misfolding and amyloid fibrillogenesis of proteins have close relationships with several neurodegenerative diseases. The present work investigates the inhibitive activities of ankaflavin (AK) and monascin (MS), two yellow pigments separated from Monascus-fermented rice, on hen egg white lysozyme (HEWL) fibrillation. The results demonstrated that AK/MS suppressed HEWL fibrillation through interfering with the nucleation period and AK was more potent. Fluorescence quenching and in silico docking studies revealed that AK/MS bond to HEWL by the formation of noncovalent forces with some critical amino acid residues that tend to form fibrils. Compared to those of AK, hydrogen bonding interactions between MS and Asn46, Trp62, and Trp63 residues in HEWL were slightly weaker. Besides, the covalent interaction between MS and HEWL with the binding site of Arg68 was found. These observations offered reasonable explanations for the difference in the mechanisms of AK and MS inhibiting HEWL fibrillogenesis. In a word, all data acquired herein indicated AK/MS as potent candidates for the improvement and treatment of neurological disorders.

Inhibition of cytotoxic self-assembly of HEWL through promoting fibrillation by new synthesized α-hydroxycarbamoylphosphinic acids

The main objective of the present study is to investigate the potency of new synthesized hydroxycarbamoyl phosphinic acid derivatives in modulating cytotoxic fibrillogenesis of hen egg white lysozyme (HEWL), as a common model in protein aggregation studies. Hydroxycarbamoyl phosphinic acid derivatives were prepared by the reaction of α-hydroxyalkylphosphinic acids with isocyanates (or isothiocyanates) in the presence of trimethylsilyl chloride (TMSCl). The designed process involves the condensation reaction leading to formation of new C sp2-P bond formation. The synthesis and purity of novel designed compounds were confirmed by NMR, LC-MS, and HPLC techniques. A range of experiments, including thioflavin T (ThT) and 8-anilino-1-naphthalenesulfonic acid (ANS) fluorescence assays, Congo red binding measurement, atomic force microscopy imaging, MTT-based cell viability and hemolysis assays were employed to investigate anti-amyloidogenic effects of tested compounds. The obtained results demonstrate that these compounds are able to significantly modulate the self-assembly process of HEWL via shortening of nucleation phase leading to the acceleration of fibrillation and appearance of very large and thick fibrils with decreased surface hydrophobicity and cytotoxicity. Based on ANS binding data, we suggest that increased exposure of hydrophobic patches of oligomeric species is the possible mechanism by which tested compounds promote self-assembly process of HEWL. Fluorescence anisotropy and molecular docking studies indicate the interaction of both synthesized compounds with HEWL, and more specifically with residues that are situated in the highly aggregation-prone β-domain region of protein. This study unveils the potential of hydroxyalkylphosphinic acids as modulators of amyloid fibrillation highlighting these compounds as a promising approach for targeting protein aggregates associated with neurodegenerative diseases.

Protonation-State Dependent Modulation of Hen Egg-White Lysozyme Fibrillation under the Influence of a Short Synthetic Peptide

Under the influence of various conditions, misfolding of soluble proteins occurs, leading to the formation of toxic insoluble amyloids. The formation and deposition of such amyloids within the body are associated with detrimental biological consequences such as the onset of several amyloid-related diseases. Previously, we established a strategy for the rational design of peptide inhibitors against amyloid formation based on the amyloidogenic-prone region of the protein. In the current study, we have designed and identified an Asp-containing rationally designed hexapeptide (SqP4) as an excellent inhibitor of hen egg-white lysozyme (HEWL) amyloid progression in vitro. First, SqP4 showed strong affinity toward the native monomeric HEWL leading to the stabilization of the native form and restriction in the unfolding process of monomeric HEWL. Second, SqP4 was found to arrest the amyloidogenic misfolded structure of HEWL in a nonfibrillar monomer-like stage. We also observed the differential effect of the protonation state of the charged amino acid (Asp) within the peptide inhibitor on the amyloid formation of HEWL and explored the reason behind the observations. The findings of this study can be implemented in future strategies for the development of potent therapeutics against other amyloid-related diseases.

Amyloid-like Aggregation of Wheat Gluten and Its Components during Cooking: Mechanisms and Structural Characterization

Amyloid-like aggregation widely occurs during the processing and production of natural proteins, with evidence indicating its presence following the thermal processing of wheat gluten. However, significant gaps remain in understanding the underlying fibrillation mechanisms and structural polymorphisms. In this study, the amyloid-like aggregation behavior of wheat gluten and its components (glutenin and gliadin) during cooking was systematically analyzed through physicochemical assessment and structural characterization. The presence of amyloid-like fibrils (AFs) was confirmed using X-ray diffraction and Congo red staining, while Thioflavin T fluorescence revealed different patterns and rates of AFs growth among wheat gluten, glutenin, and gliadin. AFs in gliadin exhibited linear growth curves, while those in gluten and glutenin showed S-shaped curves, with the shortest lag phase and fastest growth rate (t1/2 = 2.11 min) observed in glutenin. Molecular weight analyses revealed AFs primarily in the 10-15 kDa range, shifting to higher weights over time. Glutenin-derived AFs had the smallest ζ-potential value (-19.5 mV) and the most significant size increase post cooking (approximately 400 nm). AFs in gluten involve interchain reorganization, hydrophobic interactions, and conformational transitions, leading to additional cross β-sheets. Atomic force microscopy depicted varying fibril structures during cooking, notably longer, taller, and stiffer AFs from glutenin.

Synthetic macromolecular peptide-mimetics with amino acid substructure residues as protein stabilising excipients

The clinical use of protein and peptide biotherapeutics requires fabrication of stable products. This particularly concerns stability towards aggregation of proteins or peptides. Here, we tested a hypothesis that interactions between a synthetic peptide, which is an aggregation-prone region analogue, and its homologous sequence on a protein of interest, could be exploited to design excipients which stabilise the protein against aggregation. A peptide containing the analogue of lysozyme aggregation-prone region (GILQINSRW) was conjugated to a RAFT agent and used to initiate the polymerisation of N-hydroxyethyl acrylamide, generating a GILQINSRW-HEA90 polymer, which profoundly reduced lysozyme aggregation. Substitution of tryptophan in GILQINSRW with glycine, to form GILQINSRG, revealed that tryptophan is a critical amino acid in the protein stabilisation by GILQINSRW-HEA90. Accordingly, polymeric peptide-mimetics of tryptophan, phenylalanine and isoleucine, which are often present in aggregation-prone regions, were synthesized. These were based on synthetic oligomers of acrylamide derivatives of indole-3 acetic acid (IND), phenylacetic acid (PHEN), or 2-methyl butyric acid (MBA), respectively, conjugated with hydrophilic poly(N-hydroxyethyl acrylamide) blocks to form amphiphilic copolymers denoted as INDm-, PHENm- and MTBm-b-HEAn. These materials were tested as protein stabilisers and it was shown that solution properties and the abilities of these materials to stabilise insulin and the peptide IDR 1018 towards aggregation are dependent on the chemical nature of their side groups. These data suggest a structure-activity relationship, whereby the indole-based INDm-b-HEAn peptide-mimetic displays properties of a potential stabilising excipient for protein formulations.

Piezoelectric Amyloid Fibril for Energy Harvesting, Reactive Oxygen Species Generation, and Wireless Cell Therapy

Biomolecular piezoelectric materials are envisioned for advanced biomedical applications for their robust piezoelectricity, biocompatibility, and flexibility. Here, we report the piezoelectric property of amyloid fibrils derived from three distinct proteins: lysozyme, insulin, and amyloid-β. We found that piezoelectric properties are dependent on the extent of the β-sheet structure and the extent of fibril anisotropy. We have observed the piezoelectric constant value in the range of 24-42 pm/V for fibrils made of lysozyme/insulin/amyloid-β, and for the sheet/bundle-like structure of lysozyme aggregates, the value becomes 62 pm/V. These piezoelectric constant values are 4-10 times higher than the native lysozyme/insulin/amyloid proteins. Computational studies show that extension of the β-sheet structure produces an asymmetric arrangement of charges (in creating dipole moment) and mechanical stress induces an aligned orientation of these dipoles that results in a piezoelectric effect. It is shown that these piezoelectric fibrils can harvest mechanical as well as ultrasound-based energy to produce a voltage of up to 1 V and a current of up to 13 nA. These fibrils are employed for reactive oxygen species (ROS) generation under ultrasound exposure and utilized for ultrasonic degradation of organic pollutants or killing of cancer cells via intracellular ROS generation under ultrasound exposure. Our findings demonstrate that the piezoelectric property of protein fibrils has potential for wireless therapeutic applications and may have physiological roles that are yet to be explored.

Photoactivated plasmonic nanohybrid fibers with prolonged trapping of excited charge carriers for SERS analysis of biomolecules

The quest to enhance Raman spectroscopic signals through the rational design of plasmonic substrates has enabled the detection and characterization of pharmaceutically important molecules with low scattering cross-sections, such as amino acids and proteins, and is helping in making forays into the diverse field of biomedical sciences. This work presents a simple strategy for synthesizing silver nanoparticles-incorporated alumina nanofibers (Ag-AlNFs) utilizing controlled microwave synthesis for enhancing the surface-enhanced Raman chemical enhancement factor through photo-induced charge accumulation at the plasmonic-dielectric interface. The plasmonic-dielectric fibers serve as excellent charge carrier trappers, as evident from the ultrafast transient absorption spectroscopy studies. Apart from chemical enhancement, the increase in electronic surface charge also enables the protein disulfide bonds to capture these electrons and form a transient disulfide electron adduct radical, which converts to free thiol radical on dissociation. This allows protein molecules to bind to the nanoparticle's surface with the favorable silver thiol bond leading to greater surface affinity and larger SERS enhancement. The proposed Ag-AlNFs represent a cost-effective material that can be potentially used to probe biological systems in a label-free manner by photoactivating the SERS substrate for obtaining higher enhancement factors.

Mechanism of Reduced Glutathione Induced Lysozyme Defolding and Molecular Self-Assembly

The distinctive assembly behaviors of lysozyme (Lys) feature prominently in food, materials, biomedicine, and other fields and have intrigued many scholars. Although our previous work suggested that reduced glutathione (GSH) could induce lysozyme to form interfacial films at the air/water interface, the underlying mechanism is still obscure. In the present study, the effects of GSH on the disulfide bond and protein conformation of lysozyme were investigated by fluorescence spectroscopy, circular dichroism spectroscopy, and infrared spectroscopy. The findings demonstrated that GSH was able to break the disulfide bond in lysozyme molecules through the sulfhydryl/disulfide bond exchange reaction, thereby unraveling the lysozyme. The β-sheet structure of lysozyme expanded significantly, while the contents of α-helix and β-turn decreased. Furthermore, the interfacial tension and morphology analysis supported that the unfolded lysozyme tended to arrange macroscopic interfacial films at the air/water interface. It was found that pH and GSH concentrations had an impact on the aforementioned processes, with higher pH or GSH levels having a positive effect. This paper on the exploration of the mechanism of GSH-induced lysozyme interface assembly and the development of lysozyme-based green coatings has better instructive significance.

Elucidating the inhibitory effects of rationally designed novel hexapeptide against hen egg white lysozyme fibrillation at acidic and physiological pH

Inhibition of highly ordered cross-β-sheet-rich aggregates of misfolded amyloid proteins using rationally designed sequence-based short peptides is a promising therapeutic strategy for the treatment of neurodegenerative diseases. Here, we have explored the anti-amyloidogenic potency of a rationally designed hexapeptide (Tyr-Pro-Gln-Ile-Pro-Asn) on in vitro hen egg white lysozyme (HEWL) amyloid fibril formation at acidic pH and physiological pH using computational docking as well as various biophysical techniques such as fluorescence spectroscopy, UV-vis spectroscopy, FTIR spectroscopy, confocal microscopy and TEM. The peptide was designed based on the aggregation-prone region (APR) of HEWL and thus referred to as SqP1 (Sequence-based Peptide 1). SqP1 showed over 70% inhibition of HEWL amyloid formation at pH 2.2 and approximately 50% inhibition at pH 7.5. We propose that SqP1 binds to the APR of HEWL and interacts strongly with the Trp62/Trp63, ultimately stabilizing monomeric HEWL at both the pH conditions and preventing conformation changes in the structure of HEWL, leading to the formation of amyloidogenic fibrillar structures. A sequence-based peptide inhibitor of HEWL amyloid formation was not reported previously, making this a critical study that will further emphasize the importance of short synthetic peptides as amyloid inhibitors.

Analysis of the enzymatic degradation of lysozyme fibrils using a combination method of non-denaturing gel electrophoresis and double staining with Coomassie Brilliant Blue G-250 and R-250 dyes

The Amyloid fibrils of proteins are involved in various diseases, such as Alzheimer's disease. To suppress such amyloid fibrils, it is essential to develop methods to elucidate their enzymatic degradation process. Lysozyme in egg white has been well studied as a model protein of amyloid fibrils. Here, we establish a method for separating and evaluating both lysozyme fibrils and their enzymatic degradation products by combining non-denaturing gel electrophoresis and anionic dye staining with Congo red and two Coomassie brilliant blue (CBB) dyes. By combining non-denaturing gel electrophoresis and amyloid-specific Congo red staining, the separation site of lysozyme fibril was stained explicitly by Congo red and identified on the gel, and the amount of lysozyme fibrils decreased following the enzymatic degradation of lysozyme fibrils. Both lysozyme fibrils and their enzymatic degradation products were separated and examined by combining non-denaturing gel electrophoresis and double staining with CBB G-250 and R-250 dyes. Protein stained with negatively charged colloidal CBB G-250 could migrate to the anode side of electrophoresis. Following gel electrophoresis, noncolloidal CBB R-250 was used to detect lysozyme fibrils and the enzymatic degradation products. This method can be applied to investigate the enzymatic degradation process of amyloid fibrils.

Mechanistic insights into monomer level prevention of amyloid aggregation of lysozyme by glycyrrhizic acid

As the primary bioactive compound of glycyrrhiza rhizome, the triterpene glycoside conjugate Glycyrrhizic acid (GA) has demonstrated neuroprotective effects in vivo. This study evaluates the effectiveness of GA as an inhibitor of GuHCl-induced amyloid aggregation of hen egg white lysozyme (HEWL). Fibril formation as measured by Thioflavin-T fluorescence, 90⁰ light scattering, and 8-Anilinonaphthalene-1-sulfonic acid (ANS) fluorescence illustrated ∼90 % prevention of fibrils at [GA]/[HEWL] ≥2:1. Images of Transmission electron microscopy evidence for the absence of any fibril or amorphous aggregation products. The spectral characteristics of soluble HEWL were in close resemblance to unfolded monomer. Computational and fluorescence investigations performed to analyse GA-HEWL interactions demonstrated slightly higher affinity of GA to unfolded HEWL and aggregation-prone regions. The likely mechanism of monomer level aggregation prevention by GA as dermined by computational, stability, and ANS experiments illustrated that GA modulated the compactness, solvent-accessible surface, and solvent-exposed hydrophobic surfaces of aggregation-prone state of HEWL. Our findings corroborate GA as an effective inhibitor of HEWL amyloid formation. To our knowledge, GA interaction-induced inhibition of aggregation-prone states has not been previously discussed. GA's modulation of aggregation-prone states of disease-related proteins will successfully develop GA as an amyloid inhibitor for clinical trials of amyloidosis and neurodegenerative illnesses.

Roles of Tryptophan and Charged Residues on the Polymorphisms of Amyloids Formed by K-Peptides of Hen Egg White Lysozyme Investigated through Molecular Dynamics Simulations

Atomistic molecular dynamics simulations of amyloid models, consisting of the previously reported STDY-K-peptides and K-peptides from the hen egg white lysozyme (HEWL), were performed to address the effects of charged residues and pH observed in an in vitro study. Simulation results showed that amyloid models with antiparallel configurations possessed greater stability and compactness than those with parallel configurations. Then, peptide chain stretching and ordering were measured through the end-to-end distance and the order parameter, for which the amyloid models consisting of K-peptides and the STDY-K-peptides at pH 2 displayed a higher level of chain stretching and ordering. After that, the molecular mechanics energy decomposition and the radial distribution function (RDF) clearly displayed the importance of Trp62 to the K-peptide and the STDY-K-peptide models at pH 2. Moreover, the results also displayed how the negatively charged Asp52 disrupted the interaction networks and prevented the amyloid formation from STDY-K-peptide at pH 7. Finally, this study provided an insight into the interplay between pH conditions and molecular interactions underlying the formation of amyloid fibrils from short peptides contained within the HEWL. This served as a basis of understanding towards the design of other amyloids for biomaterial applications.

A Diphenylalanine Based Pentapeptide with Fibrillating Self-Assembling Properties

Peptides and their related compounds can self-assemble into diverse nanostructures of different shapes and sizes in response to various stimuli such as pH, temperature or ionic strength. Here we report the synthesis and characterization of a lysozyme derived pentapeptide and its ability to build well-defined fibrillar structures. Lysozyme FESNF peptide fragment was synthesized by solid phase peptide synthesis using the Fmoc/t-Bu strategy, purified by analytical high-performance liquid chromatography (HPLC) and its molecular weight was confirmed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Spectroscopic features of this pentapeptide were investigated by UV-visible spectroscopy and fluorimetry showing the pattern of marginal phenylalanine residues within the peptide sequence. Self-assembling properties were determined using atomic force microscopy (AFM), aggregation index and thioflavin T assay (ThT). FESNF generating fibrillar structures observed by AFM and aggregation propensity were primarily influenced by pH conditions. Moreover, the experimental data were confirmed by molecular dynamics simulation studies. The obtained fibrils will be used next to explore their potential to act as support material for medical and cosmetic application.

Amyloid fibril reduction through covalently modified lysine in HEWL and insulin

Proteins possess a variety of nucleophiles, which can carry out different reactions in the functioning cells. Proteins endogenously and synthetically can be modified through their nucleophilic sites. The roles of these chemical modifications have not been completely revealed. These modifications can alter the protein folding process. Protein folding directly affects the function of proteins. If an error in protein folding occurs, it may cause protein malfunction leading to several neurodegenerative disorders such as Alzheimer's and Parkinson's. In this study, Hen Egg White Lysozyme (HEWL) and bovine insulin, as model proteins for studying the amyloid formation, were covalently attached with 5(6)-thiophenolfluorescein. The amyloid formation of the covalently labeled lysozyme and insulin were compared with the native proteins. Interestingly, the results indicated that the covalent attachment of fluorescein slowed down the amyloid formation of HEWL and insulin significantly. The amyloid formation was examined using Thioflavin T (ThT) fluorescence assay, circular dichroism, FTIR, and gel electrophoresis. Tandem mass spectrometry was employed to identify the sites of covalent modifications in HEWL. It turned out that two surface lysine residues (K97 and K 116) in HEWL were modified. Computational studies, including docking and molecular simulations, revealed that 5(6)-thiophenolfluorescein makes several non-covalent interactions with HEWL residues, including Lys 97, leading to the reduction of the β-sheet in the protein. Additionally, AFM analysis confirmed the amyloid fibril reduction of lysine-modified bovine insulin and HEWL. Altogether, our results expand mechanistic insights into preventing amyloid formation by providing an approach for reducing amyloid formation by modifying specific lysine residues in the proteins.

Stability of hen egg-white lysozyme during embryonic development

It is of interest to determine whether and how egg-white proteins are maintained in fertile eggs. We previously observed that egg-white ovalbumin attained high stability during embryogenesis. Herein, we observed that the total mass of egg white and that of its gross protein content showed a decrease according to the days of incubation. The total bacteriolytic activity also lowered, in accord with previous observations. We purified lysozyme from egg-white samples on several incubation days. These purified lysozyme proteins were observed to have enzymatic and bacteriolytic activities against Micrococcus lysodeikticus as well as growth-inhibition potency against Staphylococcus aureus. As the embryogenesis proceeded, the purified lysozyme showed changes in Km and Vmax, a small decrease in the denaturation temperature, and symptoms of an increase in surface hydrophobicity. These results indicate that the lysozyme protein maintained its enzymatic and antibacterial activities until the late period of incubation while undergoing slight conformational changes.

One- and Two-Photon Excited Autofluorescence of Lysozyme Amyloids

Autofluorescence properties of amyloid fibrils are of much interest but, to date, the attention has been given mostly to one-photon excited fluorescence (1PEF), while the two-photon excited fluorescence (2PEF) properties of amyloids are much less explored. We investigate 1PEF and 2PEF of hen egg-white lysozyme (HEWL) in the form of monomers and fibrils. HEWL monomers feature some autofluorescence, which is enhanced in the case of fibrils. Moreover, by varying NaCl content, we introduce changes to fibrils morphology and show how the increase of the salt concentration is linked with an increase of 1PEF and 2PEF intensities. Interestingly, we observe 2PEF emission red-shifted in comparison to 1PEF. We confirm the presence of different relaxation pathways upon one- or two-photon excitation by different lifetimes of the fluorescence decays. Finally, we correlate the changes in optical properties of HEWL fibrils and monomers with salt-mediated changes in their morphology and the secondary structure.

Molecular dynamics study on the effects of charged amino acid distribution under low pH condition to the unfolding of hen egg white lysozyme and formation of beta strands

Aggregation of unfolded or misfolded proteins into amyloid fibrils can cause various diseases in humans. However, the fibrils synthesized in vitro can be developed toward useful biomaterials under some physicochemical conditions. In this study, atomistic molecular dynamics simulations were performed to address the mechanism of beta-sheet formation of the unfolded hen egg-white lysozyme (HEWL) under a high temperature and low pH. Simulations of the protonated HEWL at pH 2 and the non-protonated HEWL at pH 7 were performed at the highly elevated temperature of 450 K to accelerate the unfolding, followed by the 333 K temperature to emulate some previous in vitro studies. The simulations showed that HEWL unfolded faster, and higher beta-strand contents were observed at pH 2. In addition, one of the simulation replicas at pH 2 showed that the beta-strand forming sequence was consistent with the 'K-peptide', proposed as the core region for amyloidosis in previous experimental studies. Beta-strand formation mechanisms at the earlier stage of amyloidosis were explained in terms of the radial distribution of the amino acids. The separation between groups of positively charged sidechains from the hydrophobic core corresponded to the clustering of the hydrophobic residues and beta-strand formation.

Influence of Urea and Dimethyl Sulfoxide on K-Peptide Fibrillation

Protein fibrillation leads to formation of amyloids-linear aggregates that are hallmarks of many serious diseases, including Alzheimer's and Parkinson's diseases. In this work, we investigate the fibrillation of a short peptide (K-peptide) from the amyloidogenic core of hen egg white lysozyme in the presence of dimethyl sulfoxide or urea. During the studies, a variety of spectroscopic methods were used: fluorescence spectroscopy and the Thioflavin T assay, circular dichroism, Fourier-transform infrared spectroscopy, optical density measurements, dynamic light scattering and intrinsic fluorescence. Additionally, the presence of amyloids was confirmed by atomic force microscopy. The obtained results show that the K-peptide is highly prone to form fibrillar aggregates. The measurements also confirm the weak impact of dimethyl sulfoxide on peptide fibrillation and distinct influence of urea. We believe that the K-peptide has higher amyloidogenic propensity than the whole protein, i.e., hen egg white lysozyme, most likely due to the lack of the first step of amyloidogenesis-partial unfolding of the native structure. Urea influences the second step of K-peptide amyloidogenesis, i.e., folding into amyloids.

DMSO and TMAO-Differences in Interactions in Aqueous Solutions of the K-Peptide

Interactions between a solvent and their co-solute molecules in solutions of peptides are crucial for their stability and structure. The K-peptide is a synthetic fragment of a larger hen egg white lysozyme protein that is believed to be able to aggregate into amyloid structures. In this study, a complex experimental and theoretical approach is applied to study systems comprising the peptide, water, and two co-solutes: trimethylamide N-oxide (TMAO) or dimethyl sulfoxide (DMSO). Information about their interactions in solutions and on the stability of the K-peptide was obtained by FTIR spectroscopy and differential scanning microcalorimetry. The IR spectra of various osmolyte-water-model-peptide complexes were simulated with the DFT method (B3LYP/6-311++G(d,p)). The FTIR results indicate that both solutes are neutral for the K-peptide in solution. Both co-solutes affect the peptide to different degrees, as seen in the shape of its amide I band, and have different influences on its thermal stability. DFT calculations helped simplify the experimental data for easier interpretation.

Imidazolium-based ionic liquids with increasing alkyl chain length of cations decrease the stability and fibrillation propensity of lysozyme

Imidazolium ionic liquids with longer alkyl side chains show a larger destabilization effect on lysozyme. Increased hydrophobicity of the IL increases its binding affinity and inhibits the fibril formation of lysozyme.

The curious cases of nanoparticle induced amyloidosis during protein corona formation and anti-amyloidogenic nanomaterials: Paradox or prejudice?

Protein corona (PC) formation remains a major hurdle in the successful delivery of nanomedicines to the target sites. Interacting proteins have been reported to undergo structural changes on the nanoparticle (NP) surface which invariably impacts their biological activities. Such structural changes are the result of opening of more binding sites of proteins to adsorb on the NP surface. The process of conversion of α-helix proteins to their β-sheet enriched counterpart is termed as amyloidosis and in case of PC formation, NPs apparently play the crucial role of being the nucleation centres where this process takes place. Conversely, increasing numbers of artificial nano-chaperones are being used to treat the protein misfolding disorders. Anti-amyloidogenic nanomaterials (NM) have been gaining utmost importance in inhibiting Aβ42 (hallmark peptide for Alzheimer's disease) and Hen egg white lysozyme (HEWL, model protein for systemic amyloidosis) aggregation. Interestingly, in this process, NPs inhibit protein β-sheet enrichment. These two seemingly opposite roles of NPs, propelling confirmatory change onto the smorgasbord of adsorbed native proteins and the ability of NPs in inhibiting amyloidosis creates a paradox, which has not been discussed earlier. Here, we highlight the key points from both the facets of the NP behaviour with respect to their physicochemical properties and the nature of proteins they adsorb onto them to unravel the mystery. BRIEF: Protein corona formation remains a major hurdle in achieving the desired efficacy of nanomedicine. Proteins when interact with nanoparticle (NP) surface, undergo both structural and biological changes. Again, NPs are known to exhibit anti-amyloidogenic behaviour where these play the crucial role of preventing any change in their native structure. Such seemingly different roles of NPs need sincere inquisition.

UV Resonance Raman explores protein structural modification upon fibrillation and ligand interaction

Amyloids are proteinaceous deposits considered an underlying pathological hallmark of several degenerative diseases. The mechanism of amyloid formation and its inhibition still represent challenging issues, especially when protein structure cannot be investigated by classical biophysical techniques as for the intrinsically disordered proteins (IDPs). In this view, the need to find an alternative way for providing molecular and structural information regarding IDPs prompted us to set a novel, to our knowledge, approach focused on UV Resonance Raman (UVRR) spectroscopy. To test its applicability, we study the fibrillation of hen-egg white lysozyme (HEWL) and insulin as well as their interaction with resveratrol, employing also intrinsic fluorescence spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). The increasing of the β-sheet structure content at the end of protein fibrillation probed by FTIR occurs simultaneously with a major solvent exposure of tryptophan (Trp) and tyrosine (Tyr) residues of HEWL and insulin, respectively, as revealed by UVRR and intrinsic fluorescence spectroscopy. However, because the latter technique is successfully used when proteins naturally contain Trp residues, it shows poor performances in the case of insulin, and the information regarding its tertiary structure is exclusively provided by UVRR spectroscopy. The presence of an increased concentration of resveratrol induces mild changes in the secondary structure of both protein fibrils while remodeling HEWL fibril length and promoting the formation of amorphous aggregates in the case of insulin. Although the intrinsic fluorescence spectra of proteins are hidden by resveratrol signal, UVRR Trp and Tyr bands are resonantly enhanced, showing a good sensitivity to the presence of resveratrol and marking a modification in the noncovalent interactions in which they are involved. Our findings demonstrate that UVRR is successfully employed in the study of aggregation-prone proteins and of their interaction with ligands, especially in the case of Trp-lacking proteins.

Fibril fragments from the amyloid core of lysozyme: An accelerated molecular dynamics study

Protein aggregation and formation of amyloid fibrils are associated with many diseases and present a ubiquitous problem in protein science. Hen egg white lysozyme (HEWL) can form fibrils both from the full length protein and from its fragments. In the present study, we simulated unfolding of the amyloidogenic fragment of HEWL encompassing residues 49-101 to study the conformational aspects of amyloidogenesis. The accelerated molecular dynamics approach was used to speed up the sampling of the fragment conformers under enhanced temperature. Analysis of conformational transformation and intermediate structures was performed. During the unfolding, the novel short-living and long-living β-structures are formed along with the unstructured random coils. Such β-structure enriched monomers can interact with each other and propagate into fibril-like forms. The stability of oligomers assembled from these monomers was evaluated in the course of MD simulations with explicit water. The residues playing a key role in fibril stabilization were determined. The work provides new insights into the processes occurring at the early stages of amyloid fibril assembly.

Enhanced Antibacterial Activity of Hen Egg-White Lysozyme against Staphylococcus aureus and Escherichia coli due to Protein Fibrillation

Antibacterial agents with broad-spectrum antibacterial properties have always been in large demand. Lysozyme, a common and inexpensive protein, is widely used in food safety and biomedical applications for antibacterial purposes. However, many pathogens are lysozyme-resistant or insensitive. In this research, we investigated the antibacterial activities and mechanism of oligomers and amyloid fibrils formed from hen egg-white lysozyme (HEWL) against Staphylococcus aureus and Escherichia coli. The HEWL fibrils showed significantly enhanced antibacterial activity against both lysozyme-resistant S. aureus and lysozyme-insensitive E. coli. The HEWL oligomers, on the other hand, did not show an obvious improvement in antibacterial activity compared to native HEWL. Our results indicated that the fibrillation of HEWL can significantly enhance antibacterial activity against both S. aureus and E. coli. The natural and inexpensive HEWL amyloid fibrils can be potentially applied to antimicrobial food packaging, animal feed, antibiotic replacement, etc.

Inhibition potential evaluation of two synthetic bis-indole compounds on amyloid fibrillation: a molecular simulation study

Protein aggregation is known as the main mechanism of amyloid fibrillation in amyloidosis diseases. Recent studies confirmed that compounds with one or two indole rings have inhibitory potential against amyloid fibrillation. Herein, the interaction of two similar compounds 'bis(indolyl)-2-methyl-phenyl-methene' and 'bis(indolyl)-2-chloro-phenyl-methene' with an amyloid core model was investigated. To this aim, molecular docking and all-atom molecular dynamics (MD) simulations were used. Docking results between aggregation-prone region (APR) of hen egg-white lysozyme (HEWL) and either of ligands showed that they interact with different residues of the APR (amyloid fibril nucleus). According to MD results, bis(indolyl)-2-methyl-phenyl-methene made a distance between the two cores, which was 1.5 times greater than that bis(indolyl)-2-chloro-phenyl-methene made. Analysis of RMSD/RMSF values revealed that bis(indolyl)-2-methyl-phenyl-methene stabilized strands of A and B, while destabilized strands C and D. The hydrophobic 'methyl' functional group in bis(indolyl)-2-methyl-phenyl-methene facilitate its deep penetration between core nuclei, via destabilizing outer strands of C and D. Considering this fact that results of this study are in agreement with experimental findings, details of the discovered mechanism of interaction between ligands and HEWL's APR would be inspiring for further anti-fibrillation drug designs.Communicated by Ramaswamy H. Sarma.

Polyamines and its analogue modulates amyloid fibrillation in lysozyme: A comparative investigation

BACKGROUND

Polyamines can induce protein aggregation that can be related to the physiology of the cellular function. Polyamines have been implicated in protein aggregation which may lead to neuropathic and non neuropathic amyloidosis.

SCOPE OF REVIEW

Change in the level of polyamine concentration has been associated with ageing and neurodegeneration such as Parkinson's disease, Alzheimer's disease. Lysozyme aggregation in the presence of polyamines leads to non neuropathic amyloidosis. Polyamine analogues can suppress or inhibit protein aggregation suggesting their efficacy against amyloidogenic protein aggregates.

MAJOR CONCLUSIONS

In this study we report the comparative interactions of lysozyme with the polyamine analogue, 1-naphthyl acetyl spermine in comparison with the biogenic polyamines through spectroscopy, calorimetry, imaging and docking techniques. The findings revealed that the affinity of binding varied as spermidine > 1-naphthyl acetyl spermine > spermine. The biogenic polyamines accelerated the rate of fibrillation significantly, whereas the analogue inhibited the rate of fibrillation to a considerable extent. The polyamines bind near the catalytic diad residues viz. Glu35 and Asp52, and in close proximity of Trp62 residue. However, the analogue showed dual nature of interaction where its alkyl amine region bind in same way as the biogenic polyamines bind to the catalytic site, while the naphthyl group makes hydrophobic contacts with Trp62 and Trp63, thereby suggesting its direct influence on fibrillation.

GENERAL SIGNIFICANCE

This study, thus, potentiates, the development of a polyamine analogue that can perform as an effective inhibitor targeted towards aggregation of amyloidogenic proteins.

Human islet amyloid polypeptide (hIAPP) aggregation in type 2 diabetes: Correlation between intrinsic physicochemical properties of hIAPP aggregates and their cytotoxicity

A large number of pathological diseases are known now to be associated with the misfolding and the aberrant oligomerization and deposition of peptides and proteins into various aggregates. One of these peptides is islet amyloid polypeptide (IAPP), which is responsible for amyloid formation in type 2 diabetes. The mechanism of IAPP amyloid formation in vivo and in vitro is not well understood and the factors behind the peptide aggregates toxicity are not fully defined. Therefore, the precise nature of toxic agents still remains to be elucidated. In this context, first we used a complementary biophysical approach to undertake a systematic study of the hIAPP aggregation process with focus on the lag phase, followed by the study of their degrees of toxicity when added to the extracellular medium of pancreatic cells. The structural properties of hIAPP aggregates are characterized by evaluating their size with DLS, their surface hydrophobicity with ANS, and the interactions between monomers through the intrinsic fluorescence of aromatic residues or by the quenching of these residues mainly the tyrosine in position 37. Our results indicate that despite the method used to study hIAPP aggregation, the obtained curve is easily well fitted in a sigmoidal curve but with some differences. In fact, the analysis of the kinetic parameters gives different information about the hIAPP aggregation process such as lag time and growth rate. Moreover, a high surface hydrophobicity and small size of the aggregates, mainly for the species formed during the lag time, shows strong correlation with the cytotoxicity. These findings provide new insights into the structural changes during hIAPP aggregation and are consistent with a model in which the exposure of hydrophobic surfaces and the small size of aggregates formed during the early stage of the process are crucial for their cytotoxicity.

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.

Insoluble expression of highly soluble halophilic metal binding protein for metal ion biosorption: Application of aggregation-prone peptide from hen egg white lysozyme

Insoluble expression of intrinsically soluble proteins with native activity is potentially a promising alternative to soluble expression of folded protein or insoluble expression of unfolded protein requiring refolding. Here, we attempted to express highly soluble halophilic His-rich metal binding protein (HP) as insoluble inclusion bodies with native metal-binding activity using insolubilizing nona-peptide (Ins), GILQINSRW, derived from hen egg white lysozyme (His-InsHP). About 80% of expressed His-InsHP was localized in inclusion bodies in Na-phosphate/NaCl buffer, pH 7.4, while His-HP without Ins peptide was exclusively expressed in soluble supernatant. We report expression, purification and characterization of this insoluble His-InsHP, and its possible application for efficient biosorption and recovery of environmental metal ions, for example, by using whole bacterial cells expressing insoluble His-InsHP as a new cost-effective metal ion-adsorbent.

Rational Design of Amyloid-Like Fibrillary Structures for Tailoring Food Protein Techno-Functionality and Their Potential Health Implications

To control and enhance protein functionality is a major challenge for food scientists. In this context, research on food protein fibril formation, especially amyloid fibril formation, holds much promise. We here first provide a concise overview of conditions, which affect amyloid formation in food proteins. Particular attention is directed towards amyloid core regions because these sequences promote ordered aggregation. Better understanding of this process will be key to tailor the fibril formation process. Especially seeding, that is, adding preformed protein fibrils to protein solutions to accelerate fibril formation holds promise to tailor aggregation and fibril techno-functionality. Some studies have already indicated that food protein fibrillation indeed improves their techno-functionality. However, much more research is necessary to establish whether protein fibrils are useful in complex food systems and whether and to what extent they resist food processing unit operations. In this review the effect of amyloid formation on gelation, interfacial properties, foaming, and emulsification is discussed. Despite their prevalent role as functional structures, amyloids also receive a lot of attention due to their association with protein deposition diseases, prompting us to thoroughly investigate the potential health impact of amyloid-like aggregates in food. A literature review on the effect of the different stages of the human digestive process on amyloid toxicity leads us to conclude that food-derived amyloid fibrils (even those with potential pathogenic properties) very likely have minimal impact on human health. Nevertheless, prior to wide-spread application of the technology, it is highly advisable to further verify the lack of toxicity of food-derived amyloid fibrils.

Rutin attenuates negatively charged surfactant (SDS)-induced lysozyme aggregation/amyloid formation and its cytotoxicity

Amyloid fibrils are highly ordered protein assemblies known to contribute to the pathology of a variety of genetic and aging-associated diseases. Here, we have investigated the aggregation propensity of lysozyme in the presence of a negatively charged surfactant (SDS) and evaluated the anti-aggregation activity of rutin. Multiple approaches such as turbidity measurements, dye binding assays, intrinsic fluorescence, circular dichroism (CD), transmission electron microscopy (TEM), MTT and comet assays have been used for this purpose. We inferred that SDS induces aggregation of lysozyme in 0.2-0.6 mM concentration range while at higher concentration range (0.8-1.0 mM), it leads to solubilization/stabilization of protein. Intrinsic/extrinsic fluorescence and CD analysis confirmed significant conformational changes in lysozyme at 0.2 mM SDS. Thioflavin T (ThT), congo red binding and TEM analysis further reaffirmed the formation of lysozyme fibrils. Moreover, MTT assay demonstrated cytotoxicity of these fibrils towards neuroblastoma cell lines (SH-SY5Y) and their attenuation by rutin. Comet assay supported the cytotoxicity mechanism via DNA damage. Molecular docking results also advocate a strong interaction between lysozyme and rutin. The current study indicates a mechanistic approach assuming structural constraints and specific aromatic interactions of rutin with HEWL aggregates.

Preferential binding to zinc oxide nanoparticle interface inhibits lysozyme fibrillation and cytotoxicity

The aim of present investigation is to explore the effect of zinc oxide nanoparticles (ZnONP, 30 nm) interface on conformational dynamics and stability of lysozyme, at pH 7.4 and pH 9.0. Lysozyme adopts partially disordered conformation at pH 9.0, which adopts fibril morphology in presence of sodium dodecyl sulfate (SDS), compared to the conformation adopted at pH 7.4. However, the presence of ZnONP interface renders partially disordered lysozyme relatively regular and non-amyloidogenic conformation, and enhances the functional efficacy of lysozyme at pH 9.0. Additionally, the thermograms reveal a non-cooperative unfolding of the pH 9.0 lysozyme conformation, which accompanied with intermediate conformations that increased with increase in the interface concentration. The binding thermodynamics indicate that at pH 9.0, lysozyme conformation preferentially binds to ZnONP interface than SDS interface. The preferential binding is attributed for the resulting anti-fibrillation propensity of ZnONP interface. The data, altogether, suggest that the presence of ZnONP interface resulted in conformational rearrangements in the partially disordered lysozyme at pH 9.0 causing accumulation of non-amyloidogenic and functionally active intermediates, thus shielding the lysozyme from SDS induced fibrillation and cytotoxicity.

Paclitaxel inhibited lysozyme fibrillation by increasing colloidal stability through formation of "off-pathway" oligomers

Protein fibrillation is a challenging issue in medicine, causing many diseases, and an impediment to pharmaceutics and protein industry. Many chemicals, especially polyphenol compounds and aromatic small molecules, have been widely used as an effective strategy to combat protein fibril formation. Hence, understanding mechanisms of fibrillation inhibition and contributing forces in this process are significant. In this study, the inhibitory effect of paclitaxel on lysozyme fibrillation was investigated with respect to thermal and colloidal stability. Fibrillation was monitored with ThT fluorescence, circular dichroism, and AFM; paclitaxel-lysozyme interaction with isothermal titration calorimetry and docking; thermal and colloidal stability with differential scanning calorimetry and zeta-pulse, respectively. Paclitaxel inhibited lysozyme fibrillation, and interacted with lysozyme through hydrogen bonds and van der Waals' interactions. The viability of PC12 cells retrieved as a result of fibrillation inhibition by paclitaxel. Hydrophobic forces dominantly shielded the aggregation-prone region of lysozyme and suppressed the effective interactions between lysozyme monomers. Although paclitaxel did not affect lysozyme's thermal stability, it increased lysozyme's colloidal stability by either increasing the surface charge density or charge distribution on lysozyme. In conclusion, our results suggest a model for paclitaxel's inhibitory role through two complementary steps driving to "off-pathway" oligomer formation and attenuation of fibril formation.

Amyloid-like aggregation of designer bolaamphiphilic peptides: Effect of hydrophobic section and hydrophilic heads

Amyloid-like aggregation of natural proteins or polypeptides is an important process involved in many human diseases as well as some normal biological functions. Plenty of works have been done on this ubiquitous phenomenon, but the molecular mechanism of amyloid-like aggregation has not been fully understood yet. In this study, we showed that a series of designer bolaamphiphilic peptides could undergo amyloid-like aggregation even though they didn't possess typical β-sheet secondary structure. Through systematic amino acid substitution, we found that for the self-assembling ability, the number and species of amino acid in hydrophobic section could be variable as long as enough hydrophobic interaction is provided, while different polar amino acids as the hydrophilic heads could change the self-assembling nanostructures with their aggregating behaviors affected by pH value change. Based on these results, novel self-assembling models and aggregating mechanisms were proposed, which might provide new insight into the molecular basis of amyloid-like aggregation.

Inhibition of HEWL fibril formation by taxifolin: Mechanism of action

Among therapeutic approaches for amyloid-related diseases, attention has recently turned to the use of natural products as effective anti-aggregation compounds. Although a wealth of in vitro and in vivo evidence indicates some common inhibitory activity of these compounds, they don't generally suggest the same mechanism of action. Here, we show that taxifolin, a ubiquitous bioactive constituent of foods and herbs, inhibits formation of HEWL amyloid fibrils and their related toxicity by causing formation of very large globular, chain-like aggregates. A range of amyloid-specific techniques were employed to characterize this process. We found that taxifolin exerts its effect by binding to HEWL prefibrillar species, rather than by stabilizing the molecule in its native-like state. Furthermore, it's binding results in diverting the amyloid pathway toward formation of very large globular, chain-like aggregates with low β-sheet content and reduced solvent-exposed hydrophobic patches. ThT fluorescence measurements show that the binding capacity of taxifolin is significantly reduced, upon generation of large protofibrillar aggregates at the end of growth phase. We believe these results may help design promising inhibitors of protein aggregation for amyloid-related diseases.

Identification of an aspidospermine derivative from borage extract as an anti-amyloid compound: A possible link between protein aggregation and antimalarial drugs

A number of human diseases, including Alzheimer's and Parkinson's have been linked to amyloid formation. To search for an anti-amyloidogenic product, alkaloid enriched extract from borage leaves was examined for anti-amyloidogenic activity using Hen Egg White Lysozyme (HEWL) as a model protein. After isolation of the plant extract using rHPLC, only one fraction indicated a significant bioactivity. TEM analysis confirmed a remarkable reduction of amyloid fibrils in the presence of the bioactive fraction. To identify the effective substance in the fraction, mass spectrometry, FTIR, and NMR were performed. Our analyses determined that the bioactive compound as 1-acetyl-19,21-epoxy-15,16-dimethoxyaspidospermidine-17-ol, a derivative of aspidospermine. To investigate the mechanism of the inhibition, ANS binding, intrinsic fluorescence, and amide I content were performed in the presence of the bioactive compound. All the results confirmed the role of the compound in assisting the proper folding of the protein. In addition, molecular docking indicated the aspidospermine derivative binds the amyloidogenic region of the protein. Our results show that the alkaloid extracted from borage leaves reduces protein aggregation mediating through structural elements of the protein, promoting the correct folding of lysozyme. Since a number of aspidospermine compounds have been shown to possess potent antimalarial activities, the action of compound identified in the present study suggests a possible link between protein aggregation and aspidospermine drugs.

Molecular dynamics simulations of lysozyme-lipid systems: probing the early steps of protein aggregation

Using the molecular dynamics simulation, the role of lipids in the lysozyme transition into the aggregation-competent conformation has been clarified. Analysis of the changes of lysozyme secondary structure upon its interactions with the model bilayer membranes composed of phosphatidylcholine and its mixtures with phosphatidylglycerol (10, 40, and 80 mol%) within the time interval of 100 ns showed that lipid-bound protein is characterized by the increased content of β-structures. Along with this, the formation of protein-lipid complexes was accompanied by the increase in the gyration radius and the decrease in RMSD of polypeptide chain. The results obtained were interpreted in terms of the partial unfolding of lysozyme molecule on the lipid matrix, with the magnitude of this effect being increased with increasing the fraction of anionic lipids. Based on the results of molecular dynamics simulation, a hypothetical model of the nucleation of lysozyme amyloid fibrils in a membrane environment was suggested.

Polyphenols protect mitochondrial membrane against permeabilization induced by HEWL oligomers: Possible mechanism of action

Increasing body of evidence suggests that polyphenols frequently interacting with amyloid aggregates and/or interfering with aggregate species to bind biomembranes may serve as a therapeutic approach for the treatment of amyloid-related diseases. Hence, in the present study, the possible effects of three naturally occurring polyphenols including Curcumin, Quercetin, and Resveratrol on mitochondrial membrane permeabilization induced by Hen Egg White Lysozyme (HEWL) oligomers were investigated. Our results indicated that pre-incubation of mitochondrial homogenate with polyphenols considerably inhibit membrane permeabilization in a concentration dependent manner. In parallel, HEWL oligomers, which were co-incubated with the polyphenols, showed less effectiveness on membrane permeabilization, suggesting that toxicity of oligomers was hindered. Using a range of techniques including fluorescence quenching, Nile red binding assay, zeta potential and size measurements, CD (far- and near-UV) spectroscopy, and molecular docking, we found that the polyphenols, structure-dependently, interact with and induce conformational changes in HEWL oligomers, thereby inhibit their toxicity. We proposed a mechanism by which selected polyphenols induce their protective effects through binding to mitochondria and interfering with HEWL oligomer-membrane interactions and/or by direct interaction with HEWL oligomers, induction of conformational changes, and generating far less toxic species. However, additional studies are needed to elucidate the detailed mechanisms involved.

Mechanisms for the inhibition of amyloid aggregation by small ligands

This work investigates by biochemical, biophysical and MD techniques the opposite anti-amyloid properties of resveratrol and rosmarinic acid on the aggregation of hen egg white lysozyme (HEWL). Differences in association energy and contact maps were found that explain the different behaviours.

The formation of amyloid aggregates is the hallmark of systemic and neurodegenerative disorders, also known as amyloidoses. Many proteins have been found to aggregate into amyloid-like fibrils and this process is recognized as a general tendency of polypeptides. Lysozyme, an antibacterial protein, is a well-studied model since it is associated in human with systemic amyloidosis and that is widely available from chicken eggs (HEWL, hen egg white lysozyme). In the present study we investigated the mechanism of interaction of aggregating HEWL with rosmarinic acid and resveratrol, that we verified to be effective and ineffective, respectively, in inhibiting aggregate formation. We used a multidisciplinary strategy to characterize such effects, combining biochemical and biophysical methods with molecular dynamics (MD) simulations on the HEWL peptide 49–64 to gain insights into the mechanisms and energy variations associated to amyloid formation and inhibition. MD revealed that neither resveratrol nor rosmarinic acid were able to compete with the initial formation of the β-sheet structure. We then tested the association of two β-sheets, representing the model of an amyloid core structure. MD showed that rosmarinic acid displayed an interaction energy and a contact map comparable to that of sheet pairings. On the contrary, resveratrol association energy was found to be much lower and its contact map largely different than that of sheet pairings. The overall characterization elucidated a possible mechanism explaining why, in this model, resveratrol is inactive in blocking fibril formation, whereas rosmarinic acid is instead a powerful inhibitor.

Combined thioflavin T-Congo red fluorescence assay for amyloid fibril detection

Fluorescence represents one of the most powerful tools for the detection and structural characterization of the pathogenic protein aggregates, amyloid fibrils. The traditional approaches to the identification and quantification of amyloid fibrils are based on monitoring the fluorescence changes of the benzothiazole dye thioflavin T (ThT) and absorbance changes of the azo dye Congo red (CR). In routine screening it is usually sufficient to perform only the ThT and CR assays, but both of them, when used separately, could give false results. Moreover, fibrillization kinetics can be measured only by ThT fluorescence, while the characteristic absorption spectra and birefringence of CR represent more rigid criteria for the presence of amyloid fibrils. Therefore, it seemed reasonable to use both these dyes simultaneously, combining the advantages of each technique. To this end, we undertook a detailed analysis of the fluorescence spectral behavior of these unique amyloid tracers upon their binding to amyloid fibrils from lysozyme, insulin and an N-terminal fragment of apolipoprotein A-I with Iowa mutation. The fluorescence measurements revealed several criteria for distinguishing between fibrillar and monomeric protein states: (i) a common drastic increase in ThT fluorescence intensity; (ii) a sharp decrease in ThT fluorescence upon addition of CR; (iii) an appearance of the maximum at 535-540 nm in the CR excitation spectra; (iv) increase in CR fluorescence intensity at 610 nm. Based on these findings we designed a novel combined ThT-CR fluorescence assay for amyloid identification. Such an approach not only strengthens the reliability of the ThT assay, but also provides new opportunities for structural characterization of amyloid fibrils.