β-Amyloid peptide interactions with biomimetic membranes: A multiparametric characterization

Environmental sensitivity of amyloidogenic motifs in fungal NOD-like receptor-mediated immunity: Molecular and structural insights into amyloid assembly

This study investigates the aggregation behavior of amyloidogenic motifs associated with fungal NOD-like receptor (NLR) proteins, focusing on their sensitivity to various environmental conditions. We aimed to develop a minimal model that explains amyloid aggregation, aligning with in vivo observations and the expected role of these motifs in amyloid-based signaling. The purpose was to understand how changes in physicochemical conditions influence amyloid formation, which is crucial for fungal immune responses and has potential applications in controlling fungal infections. To achieve this, two amyloidogenic motifs, PUASM_N and PUASM_C, derived from the fungus Colletotrichum gloeosporioides, were synthesized and subjected to different conditions that simulate their natural environment. These conditions included varying pH levels, peptide concentrations, and surface adsorption properties. The aggregation kinetics, morphology, and secondary structures of the peptides were analyzed using Thioflavin T (ThT) fluorescence assay, transmission electron microscopy (TEM), and Fourier transform infrared micro-spectroscopy (micro-FTIR). The results showed that PUASM_N aggregates rapidly without a lag phase, forming long, structured fibers. In contrast, PUASM_C aggregates more slowly, with a significant lag phase, forming shorter, irregular fibers. The aggregation of PUASM_C was highly sensitive to environmental factors, such as alkaline pH and surface hydrophobicity, which accelerated its aggregation. PUASM_N, however, displayed consistent aggregation behavior under different conditions. Our findings suggest that minor environmental changes can modulate the functional roles of PUASM peptides, potentially aiding Colletotrichum gloeosporioides in regulating its antipathogenic activity in response to environmental challenges.

Disruption of PHF6 Peptide Aggregation from Tau Protein: Mechanisms of Palmatine Chloride in Preventing Early PHF6 Aggregation

The formation of neurofibrillary tangles (NFTs), composed of tau protein aggregates, is a hallmark of neurodegenerative diseases known as tauopathies, including Alzheimer's disease (AD). NFTs consist of paired helical filaments (PHFs) of tau protein with a dominant β-sheet secondary structure. Within these PHFs, the PHF6 hexapeptide (Val306-Gln-Ile-Val-Tyr-Lys311) has been commonly highlighted as a key site for tau protein nucleation. Palmatine chloride (PC) has been identified as an inhibitor of PHF6 aggregation, capable of reducing aggregation propensity at submicromolar concentrations. In pursuit of novel anti-AD drugs targeting early tau aggregation stages, we conducted an in silico study to elucidate PC's mechanism of action during PHF6 aggregation. Our observations suggest that while PHF6 can still initiate self-aggregation in the presence of PC, PC molecules subtly influence PHF6 aggregation dynamics, favoring smaller aggregates over larger complexes. The study underlined the key roles of aromatic rings in PC binding to different PHF6 aggregates by interacting through π-π stacking with the PHF6 Tyr310 side chain. The presence of aromatic rings in compounds to be able to inhibit the earlier complexation phase seems to be essential. These in silico findings lay a foundation for the design of compounds that could intervene in resolving the neurotoxicity of protein aggregates in AD.

The structure of tyrosine-10 favors ionic conductance of Alzheimer's disease-associated full-length amyloid-β channels

Amyloid β (Aβ) ion channels destabilize cellular ionic homeostasis, which contributes to neurotoxicity in Alzheimer's disease. The relative roles of various Aβ isoforms are poorly understood. We use bilayer electrophysiology, AFM imaging, circular dichroism, FTIR and fluorescence spectroscopy to characterize channel activities of four most prevalent Aβ peptides, Aβ1-42, Aβ1-40, and their pyroglutamylated forms (AβpE3-42, AβpE3-40) and correlate them with the peptides' structural features. Solvent-induced fluorescence splitting of tyrosine-10 is discovered and used to assess the sequestration from the solvent and membrane insertion. Aβ1-42 effectively embeds in lipid membranes, contains large fraction of β-sheet in a β-barrel-like structure, forms multi-subunit pores in membranes, and displays well-defined ion channel features. In contrast, the other peptides are partially solvent-exposed, contain minimal β-sheet structure, form less-ordered assemblies, and produce irregular ionic currents. These findings illuminate the structural basis of Aβ neurotoxicity through membrane permeabilization and may help develop therapies that target Aβ-membrane interactions.

A Biomimetic Multiparametric Assay to Characterise Anti-Amyloid Drugs

Alzheimer's disease (AD) is the most widespread form of senile dementia worldwide and represents a leading socioeconomic problem in healthcare. Although it is widely debated, the aggregation of the amyloid β peptide (Aβ) is linked to the onset and progression of this neurodegenerative disease. Molecules capable of interfering with specific steps in the fibrillation process remain of pharmacological interest. To identify such compounds, we have set up a small molecule screening process combining multiple experimental methods (UV and florescence spectrometry, ITC, and ATR-FTIR) to identify and characterise potential modulators of Aβ1-42 fibrillation through the description of the biochemical interactions (molecule-membrane Aβ peptide). Three known modulators, namely bexarotene, Chicago sky blue and indomethacin, have been evaluated through this process, and their modulation mechanism in the presence of a biomembrane has been described. Such a well-adapted physico-chemical approach to drug discovery proves to be an undeniable asset for the rapid characterisation of compounds of therapeutic interest for Alzheimer's disease. This strategy could be adapted and transposed to search for modulators of other amyloids such as tau protein.

Molecular Insights for Alzheimer's Disease: An Unexplored Storyline on the Nanoscale Impact of Nascent Aβ1-42 toward the Lipid Membrane

Deciphering the mechanism of Alzheimer's disease is a key element for designing an efficient therapeutic strategy. Molecular dynamics (MD) calculations, atomic force microscopy, and infrared spectroscopy were combined to investigate β-amyloid (Aβ_1-42) peptide interactions with supported lipid bilayers (SLBs). The MD simulations showed that nascent Aβ_1-42 monomers remain anchored within a model phospholipid bilayer's hydrophobic core, which suggests their stability in their native environment. We tested this prediction experimentally by studying the behavior of Aβ_1-42 monomers and oligomers when interacting with SLBs. When Aβ_1-42 monomers and oligomers were self-assembled with a lipid bilayer and deposited as an SLB, they remain within the bilayers. Their presence in the bilayers induces destabilization of the model membranes. No specific interactions between Aβ_1-42 and the SLBs were detected when SLBs free of Aβ_1-42 were exposed to Aβ_1-42. This study suggests that Aβ can remain in the membrane after cleavage by γ-secretase and cause severe damage to the membrane.

Cholesterol as a key player in amyloid β-mediated toxicity in Alzheimer’s disease

Alzheimer’s disease (AD) is a neurodegenerative disorder that is one of the most devastating and widespread diseases worldwide, mainly affecting the aging population. One of the key factors contributing to AD-related neurotoxicity is the production and aggregation of amyloid β (Aβ). Many studies have shown the ability of Aβ to bind to the cell membrane and disrupt its structure, leading to cell death. Because amyloid damage affects different parts of the brain differently, it seems likely that not only Aβ but also the nature of the membrane interface with which the amyloid interacts, helps determine the final neurotoxic effect. Because cholesterol is the dominant component of the plasma membrane, it plays an important role in Aβ-induced toxicity. Elevated cholesterol levels and their regulation by statins have been shown to be important factors influencing the progression of neurodegeneration. However, data from many studies have shown that cholesterol has both neuroprotective and aggravating effects in relation to the development of AD. In this review, we attempt to summarize recent findings on the role of cholesterol in Aβ toxicity mediated by membrane binding in the pathogenesis of AD and to consider it in the broader context of the lipid composition of cell membranes.