Aβ Amyloid Formation Research Articles

The Amyloid Cascade Hypothesis in Alzheimer's Disease: Should We Change Our Thinking?

Old age increases the risk of Alzheimer's disease (AD), the most common neurodegenerative disease, a devastating disorder of the human mind and the leading cause of dementia. Worldwide, 50 million people have the disease, and it is estimated that there will be 150 million by 2050. Today, healthcare for AD patients consumes 1% of the global economy. According to the amyloid cascade hypothesis, AD begins in the brain by accumulating and aggregating Aβ peptides and forming β-amyloid fibrils (Aβ42). However, in clinical trials, reducing Aβ peptide production and amyloid formation in the brain did not slow cognitive decline or improve daily life in AD patients. Prevention studies in cognitively unimpaired people at high risk or genetically destined to develop AD also have not slowed cognitive decline. These observations argue against the amyloid hypothesis of AD etiology, its development, and disease mechanisms. Here, we look at other avenues in the research of AD, such as the presenilin hypothesis, synaptic glutamate signaling, and the role of astrocytes and the glutamate transporter EAAT2 in the development of AD.

α-Enolase reduces cerebrovascular Aβ deposits by protecting Aβ amyloid formation.

Cerebral amyloid angiopathy (CAA) is characterized by cerebrovascular amyloid β (Aβ) deposits and causes dementia and cerebral hemorrhage. Although α-enolase (ENO1) was shown to possess multifunctional roles, its exact functions in CAA pathogenesis have not been determined. In this study, we focused on ENO1, a well-known glycolytic enzyme, which was previously identified via a proteomic approach as an upregulated protein in brain samples from patients with Alzheimer's disease (AD). We utilized the thioflavin T fluorescence assay and transmission electron microscopy to monitor the effects of ENO1 on amyloid formation by Aβ peptides. We also cultured murine primary cerebrovascular smooth muscle cells to determine the effects of ENO1 on Aβ cytotoxicity. To investigate the effects of ENO1 in vivo, we infused ENO1 or a vehicle control into the brains of APP23 mice, atransgenicmodelofAD/CAA, using a continuous infusion system, followed by a cognitive test and pathological and biochemical analyses. We found that novel functions of ENO1 included interacting with Aβ and inhibiting its fibril formation, disrupting Aβ fibrils, and weakening the cytotoxic effects of these fibrils via proteolytic degradation of Aβ peptide. We also demonstrated that infusion of ENO1 into APP23 mouse brains reduced cerebrovascular Aβ deposits and improved cognitive impairment. In addition, we found that enzymatically inactivated ENO1 failed to inhibit Aβ fibril formation and fibril disruption. The proteolytic activity of ENO1 may thus underlie the enzyme's cytoprotective effect and clearance of Aβ from the brain, and ENO1 may be a therapeutic target in CAA.

The amyloid-inhibiting NCAM-PrP peptide targets Aβ peptide aggregation in membrane-mimetic environments

SummarySubstantial research efforts have gone into elucidating the role of protein misfolding and self-assembly in the onset and progression of Alzheimer’s disease (AD). Aggregation of the Amyloid-β (Aβ) peptide into insoluble fibrils is closely associated with AD. Here, we use biophysical techniques to study a peptide-based approach to target Aβ amyloid aggregation. A peptide construct, NCAM-PrP, consists of a largely hydrophobic signal sequence linked to a positively charged hexapeptide. The NCAM-PrP peptide inhibits Aβ amyloid formation by forming aggregates which are unavailable for further amyloid aggregation. In a membrane-mimetic environment, Aβ and NCAM-PrP form specific heterooligomeric complexes, which are of lower aggregation states compared to Aβ homooligomers. The Aβ:NCAM-PrP interaction appears to take place on different aggregation states depending on the absence or presence of a membrane-mimicking environment. These insights can be useful for the development of potential future therapeutic strategies targeting Aβ at several aggregation states.

Cold Atmospheric Plasma Modification of Amyloid β.

Cold atmospheric plasma (CAP) has attracted much attention in the fields of biotechnology and medicine owing to its potential utility in clinical applications. Recently accumulating evidence has demonstrated that CAP influences protein structures. However, there remain open questions regarding the molecular mechanisms behind the CAP-induced structural perturbations of biomacromolecules. Here, we investigated the potential effects of CAP irradiation of amyloid β (Aβ), an amyloidogenic protein associated with Alzheimer’s disease. Using nuclear magnetic resonance spectroscopy, we observed gradual spectral changes in Aβ after a 10 s CAP pretreatment, which also suppressed its fibril formation, as revealed by thioflavin T assay. As per mass spectrometric analyses, these effects were attributed to selective oxidation of the methionine residue (Met) at position 35. Interestingly, this modification occurred when Aβ was dissolved into a pre-irradiated buffer, indicating that some reactive species oxidize the Met residue. Our results strongly suggest that the H2O2 generated in the solution by CAP irradiation is responsible for Met oxidation, which inhibits Aβ amyloid formation. The findings of the present study provide fundamental insights into plasma biology, giving clues for developing novel applications of CAP.

Modeling the spatial propagation of Aβ oligomers in Alzheimer’s Disease

Recent advances in the study of Alzheimer’s Disease and the role of Aβ amyloid formation have caused the focus of biologists to progressively shift towards the smaller protein assemblies, the oligomers. These appear very early on in the disease progression and they seem to be the most infectious species for the neurons. We suggest a model of spatial propagation of Aβ oligomers in the vicinity of a few neurons, without considering the formation of large fibrils or plaques. We also include a simple representation of the oligomers neurotoxic effect. A numerical study reveals that the oligomers spatial dynamics are very sensitive to the balance between their diffusion and their replication, and that the outcome in terms of the progression of AD strongly depends on it.

Apolipoprotein E impairs amyloid-β fibril elongation and maturation.

Alzheimer's disease (AD) is strongly linked to amyloid depositions of the Aβ peptide (Aβ). The lipid-binding protein apolipoprotein E (ApoE) has been found to interfere with Aβ amyloid formation and to exert a strong clinical impact to the pathology of AD. The APOE gene exists in three allelic isoforms represented by APOE ε2, APOE ε3, and APOE ε4. Carriers of the APOE ε4 variant display a gene dose-dependent increased risk of developing the disease. Aβ amyloids are formed via a nucleation-dependent mechanism where free monomers are added onto a nucleus in a template-dependent manner. Using a combination of surface plasmon resonance and thioflavin-T assays, we here show that ApoE can target the process of fibril elongation and that its interference effectively prevents amyloid maturation. We expose a complex equilibrium where the concentration of ApoE, Aβ monomers, and the amount of already formed Aβ fibrils will affect the relative proportion and formation rate of mature amyloids versus alternative assemblies. The result illustrates a mechanism which may affect both the clearance rate of Aβ assemblies invivo and the population of cytotoxic Aβ assemblies.

The triphenylmethane dye brilliant blue G is only moderately effective at inhibiting amyloid formation by human amylin or at disaggregating amylin amyloid fibrils, but interferes with amyloid assays; Implications for inhibitor design.

The development of inhibitors of islet amyloid formation is important as pancreatic amyloid deposition contributes to type-2 diabetes and islet transplant failure. The Alzheimer’s Aβ peptide and human amylin (h-amylin), the polypeptide responsible for amyloid formation in type-2 diabetes, share common physio-chemical features and some inhibitors of Aβ also inhibit amyloid formation by h-amylin and vice versa. Thus, a popular and potentially useful strategy to find lead compounds for anti-amylin amyloid agents is to examine compounds that have effects on Aβ amyloid formation. The triphenylmethane dye, brilliant blue G (BBG, Sodium;3-[[4-[(E)-[4-(4-ethoxyanilino)phenyl]-[4-[ethyl-[(3-sulfonatophenyl)methyl]azaniumylidene]-2-methylcyclohexa-2,5-dien-1-ylidene]methyl]-N-ethyl-3-methylanilino]methyl]benzenesulfonate) has been shown to modulate Aβ amyloid formation and inhibit Aβ induced toxicity. However, the effects of BBG on h-amylin have not been examined, although other triphenylmethane derivatives inhibit h-amylin amyloid formation. The compound has only a modest impact on h-amylin amyloid formation unless it is added in significant excess. BBG also remodels preformed h-amylin amyloid fibrils if added in excess, however BBG has no significant effect on h-amylin induced toxicity towards cultured β-cells or cultured CHO-T cells except at high concentrations. BBG is shown to interfere with standard thioflavin-T assays of h-amylin amyloid formation and disaggregation, highlighting the difficulty of interpreting such experiments in the absence of other measurements. BBG also interferes with ANS based assays of h-amylin amyloid formation. The work highlights the differences between inhibition of Aβ and h-amylin amyloid formation, illustrates the limitation of using Aβ inhibitors as leads for h-amylin amyloid inhibitors, and reinforces the difficulties in interpreting dye binding assays of amyloid formation.

Molecular insights into the surface-catalyzed secondary nucleation of amyloid-β40 (Aβ40) by the peptide fragment Aβ16-22.

Understanding the structural mechanism by which proteins and peptides aggregate is crucial, given the role of fibrillar aggregates in debilitating amyloid diseases and bioinspired materials. Yet, this is a major challenge as the assembly involves multiple heterogeneous and transient intermediates. Here, we analyze the co-aggregation of Aβ40 and Aβ16-22, two widely studied peptide fragments of Aβ42 implicated in Alzheimer's disease. We demonstrate that Aβ16-22 increases the aggregation rate of Aβ40 through a surface-catalyzed secondary nucleation mechanism. Discontinuous molecular dynamics simulations allowed aggregation to be tracked from the initial random coil monomer to the catalysis of nucleation on the fibril surface. Together, the results provide insight into how dynamic interactions between Aβ40 monomers/oligomers on the surface of preformed Aβ16-22 fibrils nucleate Aβ40 amyloid assembly. This new understanding may facilitate development of surfaces designed to enhance or suppress secondary nucleation and hence to control the rates and products of fibril assembly.

Transthyretin Interferes with Aβ Amyloid Formation by Redirecting Oligomeric Nuclei into Non-Amyloid Aggregates

The pathological Aβ aggregates associated with Alzheimer's disease follow a nucleation-dependent path of formation. A nucleus represents an oligomeric assembly of Aβ peptides that acts as a template for subsequent incorporation of monomers to form a fibrillar structure. Nuclei can form de novo or via surface-catalyzed secondary nucleation, and the combined rates of elongation and nucleation control the overall rate of fibril formation. Transthyretin (TTR) obstructs Aβ fibril formation in favor of alternative non-fibrillar assemblies, but the mechanism behind this activity is not fully understood. This study shows that TTR does not significantly disturb fibril elongation; rather, it effectively interferes with the formation of oligomeric nuclei. We demonstrate that this interference can be modulated by altering the relative contribution of elongation and nucleation, and we show how TTR's effects can range from being essentially ineffective to almost complete inhibition of fibril formation without changing the concentration of TTR or monomeric Aβ.

Foldamer-Mediated Structural Rearrangement Attenuates Aβ Oligomerization and Cytotoxicity.

The conversion of the native random coil amyloid beta (Aβ) into amyloid fibers is thought to be a key event in the progression of Alzheimer's disease (AD). A significant body of evidence suggests that the highly dynamic Aβ oligomers are the main causal agent associated with the onset of AD. Among many potential therapeutic approaches, one is the modulation of Aβ conformation into off-pathway structures to avoid the formation of the putative neurotoxic Aβ oligomers. A library of oligoquinolines was screened to identify antagonists of Aβ oligomerization, amyloid formation, and cytotoxicity. A dianionic tetraquinoline, denoted as 5, was one of the most potent antagonists of Aβ fibrillation. Biophysical assays including amyloid kinetics, dot blot, ELISA, and TEM show that 5 effectively inhibits both Aβ oligomerization and fibrillation. The antagonist activity of 5 toward Aβ aggregation diminishes with sequence and positional changes in the surface functionalities. 5 binds to the central discordant α-helical region and induces a unique α-helical conformation in Aβ. Interestingly, 5 adjusts its conformation to optimize the antagonist activity against Aβ. 5 effectively rescues neuroblastoma cells from Aβ-mediated cytotoxicity and antagonizes fibrillation and cytotoxicity pathways of secondary nucleation induced by seeding. 5 is also equally effective in inhibiting preformed oligomer-mediated processes. Collectively, 5 induces strong secondary structure in Aβ and inhibits its functions including oligomerization, fibrillation, and cytotoxicity.

Gold Nanoparticles as a Probe for Amyloid-β Oligomer and Amyloid Formation.

The process of amyloid-β (Aβ) amyloid formation is pathologically linked to Alzheimer's disease (AD). The identification of Aβ amyloids and intermediates that are crucial players in the pathology of AD is critical for exploring the underlying mechanism of Aβ aggregation and the diagnosis of the disease. Herein, we performed a gold nanoparticle (AuNP)-based study to detect the formation of Aβ amyloid fibrils and oligomers. Our results demonstrate that the intensity of the surface plasmon resonance (SPR) absorption band of the AuNPs is sensitive to the quantity of Aβ40 amyloids. This allows the SPR assay to be used for detection and semi-quantification of Aβ40 amyloids, and characterization of the kinetics of Aβ amyloid formation. Furthermore, our study demonstrates that the SPR band intensity of the AuNPs is sensitive to the presence of oligomers of both Aβ40 and an Aβ40 mutant, which forms more stable oligomers. The kinetics of the stable oligomer formation of the Aβ40 mutant can also be monitored following the SPR band intensity change of AuNPs. Our results indicate that this nanoparticle based method can be used for mechanistic studies of early protein self-assembly and fibrillogenesis.

Designed Cell-Penetrating Peptides for Inhibition of Amyloid-Beta (Aβ) Amyloid Formation and Cytotoxicity

Several neurodegenerative diseases are characterized by self-assembly of proteins or peptides into aggregates termed amyloid, which share various physicochemical features: a fibrillar morphology, a predominantly β-sheet secondary structure, insolubility in common solvents and detergents, and protease resistance. These so-called amyloid diseases include Alzheimer's disease (AD), Huntington's disease, Parkinson's disease and prion diseases. Despite intense research efforts over several decades, the pathophysiology and interlinkage of these diseases remains unresolved. This is mainly due to the transient nature of the different aggregation states along the amyloid formation pathway, which impedes identification of the cytotoxic species. Recently, a peptide derived from the unprocessed N-terminus of cellular prion protein (PrPC) was shown to function as a cell-penetrating peptide (CPP) and to significantly reduce levels of the disease-associated scrapie isoform (PrPSc) in prion-infected cells. This peptide comprises two segments: a hydrophobic signal sequence, to which the CPP property is attributed, followed by a polycationic nuclear localization signal (NLS)-like sequence that interacts with PrPSc. Interestingly, the anti-prion efficiency of the peptide could be enhanced by substitution of the PrPC signal sequence with a more flexible signal sequence from the neural cell adhesion molecule-1 (NCAM-1). Here, we extended the study towards amyloid-beta (Aβ) aggregation, which is associated with AD. We investigated the amyloid formation and cytotoxicity of the Aβ-inhibitor complexes using thioflavin T fluorescence assays, AFM, NMR, cell proliferation assays and fluorescence imaging methods. We report that the NCAM-1-based inhibitor stabilizes Aβ in a non-amyloid state and protects neuronal cells against Aβ-induced neurotoxicity. Moreover, we show that the replacement of the PrPC NLS-like sequence with a NLS-like segment from Aβ results in similar CPP-functionality and anti-Aβ effects. Our findings reveal a general underlying principle for the inhibition of pathogenic protein aggregation that will allow for the design of a ‘universal’ peptide-based inhibitor.

One of the possible mechanisms of amyloid fibrils formation based on the sizes of primary and secondary folding nuclei of Aβ40 and Aβ42.

In the presented paper, theoretical as well as electron microscopy and X-ray diffraction experimental approaches were employed for studding the process of Aβ amyloid formation. Using quantitative estimates of a number of monomers which form the nuclei of amyloid fibrils the sizes of folding nuclei of amyloid fibrils for Aβ40 and 42 have been determined for the first time. We have shown that the size of the primary nucleus of Aβ42 peptide fibrils corresponds to 3 monomers, the size of the secondary nucleus for this peptide is 2 monomers. Applying the same analysis to Aβ40 we conclude that the size of the primary nucleus is 2 monomers, and the size of the secondary nucleus is one monomer. Summation of our theoretical and experimental results has allowed us to propose a new model of the structural organization of amyloid fibrils. Our model suggests that the generation of fibrils takes place along the following simplified pathway: a monomer→a ring oligomer→a mature fibril consisting of ring oligomers. These data shed more light upon our understanding of what sizes of the oligomers could represent main targets for future therapies (tetramers for Aβ42 and trimers for Aβ40), and aid in the development of inhibitors of Aβ40 and 42 oligomer formation.

(R)‐α‐trifluoromethylalanine containing short peptide in the inhibition of amyloid peptide fibrillation

The extracellular deposition of insoluble amyloid fibrils resulting from the aggregation of the amyloid-β (Aβ) is a pathological feature of neuronal loss in Alzheimer's disease (AD). Numerous small molecules have been reported to interfere with the process of Aβ aggregation. Compounds containing aromatic structures, hydrophobic amino acids and/or the α-aminoisobutyric acid (Aib) as β-sheet breaker elements have been reported to be effective inhibitors of Aβ aggregation. We synthesized two peptides, one containing the Aib amino acid and the other including its trifluoromethylated analog (R)-α-Trifluoromethylalanine ((R)-Tfm-Alanine) and we evaluated the impact of these peptides on Aβ amyloid formation. The compounds were tested by standard methods such as thioflavin-T fluorescence spectroscopy and transmission electron microscopy but also by circular dichroism, liquid state nuclear magnetic resonance (NMR) and NMR saturation transfer difference (STD) experiments to further characterize the effect of the two molecules on Aβ structure and on the kinetics of depletion of monomeric, soluble Aβ. Our results demonstrate that the peptide containing Aib reduces the quantity of aggregates containing β-sheet structure but slightly inhibits Aβ fibril formation, while the molecule including the trifluoromethyl (Tfm) group slows down the kinetics of Aβ fibril formation, delays the random coil to β-sheet structure transition and induces a change in the oligomerization pathway. These results suggest that the hydrophobic Tfm group has a better affinity with Aβ than the methyl groups of the Aib and that this Tfm group is effective and important in preventing the Aβ aggregation.

Anthocyanin suppresses the toxicity of Aβ deposits through diversion of molecular forms in in vitro and in vivo models of Alzheimer's disease

Objectives: The pathogenesis of Alzheimer's disease (AD) is strongly correlated with the aggregation and deposition of the amyloid beta (Aβ1–42) peptide in fibrillar form, and many studies have shown that plant-derived polyphenols are capable of attenuating AD progression in various disease models. In this study, we set out to correlate the effects of anthocyanoside extracts (Vaccinium myrtillus anthocyanoside (VMA)) obtained from bilberry on the in vitro progression of Aβ fibril formation with the in vivo effects of this compound on AD pathogenesis.Methods: Thioflavin T fluorescence assays and atomic force microscopy were used to monitor Aβ amyloid formation in in vitro assays. Effects of Aβ amyloids on cellular viability were assayed using cultured Neuro2a cells. Cognitive effects were probed using mice that simultaneously expressed mutant human Aβ precursor and mutant presenilin-2.Results: Addition of VMA inhibited the in vitro formation of Aβ peptide fibrils and also reduced the toxicity of these aggregates toward Neuro2a cells. A diet containing 1% VMA prevented the cognitive degeneration in AD mice. Curiously, this diet-derived retention of cognitive ability was not accompanied by a reduction in aggregate deposition in brains; rather, an increase in insoluble deposits was observed compared with mice raised on a control diet.Discussion: The paradoxical increase in insoluble deposits caused by VMA suggests that these polyphenols divert Aβ aggregation to an alternate, non-toxic form. This finding underscores the complex effects that polyphenol compounds may exert on amyloid deposition in vivo.

A human monoclonal IgG that binds aβ assemblies and diverse amyloids exhibits anti-amyloid activities in vitro and in vivo.

Alzheimer's disease (AD) and familial Danish dementia (FDD) are degenerative neurological diseases characterized by amyloid pathology. Normal human sera contain IgG antibodies that specifically bind diverse preamyloid and amyloid proteins and have shown therapeutic potential in vitro and in vivo. We cloned one of these antibodies, 3H3, from memory B cells of a healthy individual using a hybridoma method. 3H3 is an affinity-matured IgG that binds a pan-amyloid epitope, recognizing both Aβ and λ Ig light chain (LC) amyloids, which are associated with AD and primary amyloidosis, respectively. The pan-amyloid-binding properties of 3H3 were demonstrated using ELISA, immunohistochemical studies, and competition binding assays. Functional studies showed that 3H3 inhibits both Aβ and LC amyloid formation in vitro and abrogates disruption of hippocampal synaptic plasticity by AD-patient-derived soluble Aβ in vivo. A 3H3 single-chain variable fragment (scFv) retained the binding specificity of the 3H3 IgG and, when expressed in the brains of transgenic mice using an adeno-associated virus (AAV) vector, decreased parenchymal Aβ amyloid deposition in TgCRND8 mice and ADan (Danish Amyloid) cerebral amyloid angiopathy in the mouse model of FDD. These data indicate that naturally occurring human IgGs can recognize a conformational, amyloid-specific epitope and have potent anti-amyloid activities, providing a rationale to test their potential as antibody therapeutics for diverse neurological and other amyloid diseases.

General amyloid inhibitors? A critical examination of the inhibition of IAPP amyloid formation by inositol stereoisomers.

Islet amyloid polypeptide (IAPP or amylin) forms amyloid deposits in the islets of Langerhans; a process that is believed to contribute to the progression of type 2 diabetes and to the failure of islet transplants. An emerging theme in amyloid research is the hypothesis that the toxic species produced during amyloid formation by different polypeptides share common features and exert their effects by common mechanisms. If correct, this suggests that inhibitors of amyloid formation by one polypeptide might be effective against other amyloidogenic sequences. IAPP and Aβ, the peptide responsible for amyloid formation in Alzheimer's disease, are particularly interesting in this regard as they are both natively unfolded in their monomeric states and share some common characteristics. Comparatively little effort has been expended on the design of IAPP amyloid inhibitors, thus it is natural to inquire if Aβ inhibitors are effective against IAPP, especially since no IAPP inhibitors have been clinically approved. A range of compounds inhibit Aβ amyloid formation, including various stereoisomers of inositol. Myo-, scyllo-, and epi-inositol have been shown to induce conformational changes in Aβ and prevent Aβ amyloid fibril formation by stabilizing non-fibrillar β-sheet structures. We investigate the ability of inositol stereoisomers to inhibit amyloid formation by IAPP. The compounds do not induce a conformational change in IAPP and are ineffective inhibitors of IAPP amyloid formation, although some do lead to modest apparent changes in IAPP amyloid fibril morphology. Thus not all classes of Aβ inhibitors are effective against IAPP. This work provides a basis of comparison to work on polyphenol based inhibitors of IAPP amyloid formation and helps provide clues as to the features which render them effective. The study also helps provide information for further efforts in rational inhibitor design.

Improved chemical synthesis of hydrophobic Aβ peptides using addition of C‐terminal lysines later removed by carboxypeptidase B

Many amyloidogenic peptides are highly hydrophobic, introducing significant challenges to obtaining high quality peptides by chemical synthesis. For example, while good yield and purity can be obtained in the solid-phase synthesis of the Alzheimer's plaque peptide Aβ40, addition of a C-terminal Ile-Ala sequence to generate the more toxic Aβ42 molecule creates a much more difficult synthesis resulting in low yields and purities. We describe here a new method that significantly improves the Fmoc solid-phase synthesis of Aβ peptides. In our method, Lys residues are linked to the desired peptide's C-terminus through standard peptide bonds during the synthesis. These Lys residues are then removed post-purification using immobilized carboxypeptidase B (CPB). With this method we obtained both Aβ42 and Aβ46 of superior quality that, for Aβ42, rivals that obtained by recombinant expression. Intriguingly, the method appears to provide independent beneficial effects on both the total synthetic yield and on purification yield and final purity. Reversible Lys addition with CPB removal should be a generally useful method for making hydrophobic peptides that is applicable to any sequence not ending in Arg or Lys. As expected from the additional hydrophobicity of Aβ46, which is extended from the sequence Aβ42 by a C-terminal Thr-Val-Ile-Val sequence, this peptide makes typical amyloid at rates significantly faster than for Aβ42 or Aβ40. The enhanced amyloidogenicity of Aβ46 suggests that, even though it is present in relatively low amounts in the human brain, it could play a significant role in helping to initiate Aβ amyloid formation.

Inhibiting and Reversing Amyloid‐β Peptide (1–40) Fibril Formation with Gramicidin S and Engineered Analogues

In Alzheimer's disease, amyloid-β (Aβ) peptides aggregate into extracellular fibrillar deposits. Although these deposits may not be the prime cause of the neurodegeneration that characterizes this disease, inhibition or dissolution of amyloid fibril formation by Aβ peptides is likely to affect its development. ThT fluorescence measurements and AFM images showed that the natural antibiotic gramicidin S significantly inhibited Aβ amyloid formation in vitro and could dissolve amyloids that had formed in the absence of the antibiotic. In silico docking suggested that gramicidin S, a cyclic decapeptide that adopts a β-sheet conformation, binds to the Aβ peptide hairpin-stacked fibril through β-sheet interactions. This may explain why gramicidin S reduces fibril formation. Analogues of gramicidin S were also tested. An analogue with a potency that was four-times higher than that of the natural product was identified.

NMR characterization of the interaction of GroEL with amyloid β as a model ligand

Here we report an NMR study on the substrate interaction modes of GroEL using amyloid β (Aβ) as a model ligand. We found that GroEL could suppress Aβ(1–40) amyloid formation by interacting with its two hydrophobic segments Leu17-Ala21 and Ala30-Val36, which involve key residues in fibril formation. The binding site of Aβ(1–40) was mapped on a pair of α-helices located in the GroEL apical domain. These results provide insights into chaperonin recognition of amyloidogenic proteins of pathological interest.