Fibril Structure Research Articles

Roles of soybean β-conglycinin subunit fractions in fibril formation and the effects of glycinin on them

This research is aimed at exploring the fibrillation of soybean β-conglycinin (7S) subunits (αα′ and β) at 90 °C and pH 2.0, as well as the effects of glycinin (11S) on them. Fibril formation kinetics was monitored by measuring changes in thioflavin T (Th T) fluorescence intensity of the proteins. This analysis showed that αα′ subunits had a higher fibrillation capacity but slower fibril formation rate than the β subunit. Glycinin accelerated the rate of fibrillation of the αα′ and β subunits but weakened the fibril structure. The size of the fibrils first decreased and then increased with increasing heating time. Circular dichroism and intrinsic fluorescence spectroscopy analysis indicated that the β-sheet structure and hydrophobic interactions were important for the generation of ordered fibrils. Shear viscosity and transmission electron microscopy analysis suggested that the αα′ subunits formed relatively rigid fibrils that led to a high solution viscosity. In contrast, β subunit fibrils became unstable after prolonged heating, forming shorter fibrils (fragments) that tended to aggregate, which led to a lower solution viscosity. This research also suggested that the extension region of αα′ subunits played an important role in fibrillation, and the presence of the highly hydrophobic basic polypeptides of glycinin might be the main reason for the inhibition of soy protein fibrillation. Our analysis of soy protein fibrillization at the subunit level provides insights that might enhance the future application of soy protein fibrils as functional ingredients in foods.

Cryo-EM structures of lipidic fibrils of amyloid-β (1-40)

Alzheimer’s disease (AD) is a progressive and incurable neurodegenerative disease characterized by the extracellular deposition of amyloid plaques. Investigation into the composition of these plaques revealed a high amount of amyloid-β (Aβ) fibrils and a high concentration of lipids, suggesting that fibril-lipid interactions may also be relevant for the pathogenesis of AD. Therefore, we grew Aβ40 fibrils in the presence of lipid vesicles and determined their structure by cryo-electron microscopy (cryo-EM) to high resolution. The fold of the major polymorph is similar to the structure of brain-seeded fibrils reported previously. The majority of the lipids are bound to the fibrils, as we show by cryo-EM and NMR spectroscopy. This apparent lipid extraction from vesicles observed here in vitro provides structural insights into potentially disease-relevant fibril-lipid interactions.

O-GlcNAc forces an α-synuclein amyloid strain with notably diminished seeding and pathology.

Amyloid-forming proteins such α-synuclein and tau, which are implicated in Alzheimer's and Parkinson's disease, can form different fibril structures or strains with distinct toxic properties, seeding activities and pathology. Understanding the determinants contributing to the formation of different amyloid features could open new avenues for developing disease-specific diagnostics and therapies. Here we report that O-GlcNAc modification of α-synuclein monomers results in the formation of amyloid fibril with distinct core structure, as revealed by cryogenic electron microscopy, and diminished seeding activity in seeding-based neuronal and rodent models of Parkinson's disease. Although the mechanisms underpinning the seeding neutralization activity of the O-GlcNAc-modified fibrils remain unclear, our in vitro mechanistic studies indicate that heat shock proteins interactions with O-GlcNAc fibril inhibit their seeding activity, suggesting that the O-GlcNAc modification may alter the interactome of the α-synuclein fibrils in ways that lead to reduce seeding activity in vivo. Our results show that posttranslational modifications, such as O-GlcNAc modification, of α-synuclein are key determinants of α-synuclein amyloid strains and pathogenicity.

Copper(II) Can Kinetically Trap Arctic and Italian Amyloid-β40 as Toxic Oligomers, Mimicking Cu(II) Binding to Wild-Type Amyloid-β42: Implications for Familial Alzheimer's Disease.

The self-association of amyloid-β (Aβ) peptide into neurotoxic oligomers is believed to be central to Alzheimer's disease (AD). Copper is known to impact Aβ assembly, while disrupted copper homeostasis impacts phenotype in Alzheimer's models. Here we show the presence of substoichiometric Cu(II) has very different impacts on the assembly of Aβ40 and Aβ42 isoforms. Globally fitting microscopic rate constants for fibril assembly indicates copper will accelerate fibril formation of Aβ40 by increasing primary nucleation, while seeding experiments confirm that elongation and secondary nucleation rates are unaffected by Cu(II). In marked contrast, Cu(II) traps Aβ42 as prefibrillar oligomers and curvilinear protofibrils. Remarkably, the Cu(II) addition to preformed Aβ42 fibrils causes the disassembly of fibrils back to protofibrils and oligomers. The very different behaviors of the two Aβ isoforms are centered around differences in their fibril structures, as highlighted by studies of C-terminally amidated Aβ42. Arctic and Italian familiar mutations also support a key role for fibril structure in the interplay of Cu(II) with Aβ40/42 isoforms. The Cu(II) dependent switch in behavior between nonpathogenic Aβ40 wild-type and Aβ40 Arctic or Italian mutants suggests heightened neurotoxicity may be linked to the impact of physiological Cu(II), which traps these familial mutants as oligomers and curvilinear protofibrils, which cause membrane permeability and Ca(II) cellular influx.

Local structural preferences in shaping tau amyloid polymorphism

Tauopathies encompass a group of neurodegenerative disorders characterised by diverse tau amyloid fibril structures. The persistence of polymorphism across tauopathies suggests that distinct pathological conditions dictate the adopted polymorph for each disease. However, the extent to which intrinsic structural tendencies of tau amyloid cores contribute to fibril polymorphism remains uncertain. Using a combination of experimental approaches, we here identify a new amyloidogenic motif, PAM4 (Polymorphic Amyloid Motif of Repeat 4), as a significant contributor to tau polymorphism. Calculation of per-residue contributions to the stability of the fibril cores of different pathologic tau structures suggests that PAM4 plays a central role in preserving structural integrity across amyloid polymorphs. Consistent with this, cryo-EM structural analysis of fibrils formed from a synthetic PAM4 peptide shows that the sequence adopts alternative structures that closely correspond to distinct disease-associated tau strains. Furthermore, in-cell experiments revealed that PAM4 deletion hampers the cellular seeding efficiency of tau aggregates extracted from Alzheimer’s disease, corticobasal degeneration, and progressive supranuclear palsy patients, underscoring PAM4’s pivotal role in these tauopathies. Together, our results highlight the importance of the intrinsic structural propensity of amyloid core segments to determine the structure of tau in cells, and in propagating amyloid structures in disease.

How Chromophore Labels Shape the Structure and Dynamics of a Peptide Hydrogel.

Biocompatible and functionalizable hydrogels have a wide range of (potential) medicinal applications. The hydrogelation process, particularly for systems with very low polymer weight percentages (<1 wt %), remains poorly understood, making it challenging to predict the self-assembly of a given molecular building block into a hydrogel. This severely hinders the rational design of self-assembled hydrogels. In this study, we demonstrate the impact of an N-terminal group on the self-assembly and rheology of the peptide hydrogel hFF03 (hydrogelating, fibril forming peptide 03) using molecular dynamics simulations, oscillatory shear rheology, and circular dichroism spectroscopy. We find that the chromophore and even its specific regioisomers have a significant influence on the microscopic structure and dynamics of the self-assembled fibril, and on the macroscopic mechanical properties. This is because the chromophore influences the possible salt bridges, which form and stabilize the fibril formation. Furthermore, we find that the solvation shell fibrils by itself cannot explain the viscoelasticity of hFF03 hydrogels. Our atomistic model of the hFF03 fibril formation enables a more rational design of these hydrogels. In particular, altering the N-terminal chromophore emerges as a design strategy to tune the mechanic properties of these self-assembled peptide hydrogels.

Amyloid-α Peptide Formed through Alternative Processing of the Amyloid Precursor Protein Attenuates Alzheimer's Amyloid-β Toxicity via Cross-Chaperoning.

Amyloid aggregation is a key feature of Alzheimer's disease (AD) and a primary target for past and present therapeutic efforts. Recent research is making it increasingly clear that the heterogeneity of amyloid deposits, extending past the commonly targeted amyloid-β (Aβ), must be considered for successful therapy. We recently demonstrated that amyloid-α (Aα or p3), a C-terminal peptidic fragment of Aβ, aggregates rapidly to form amyloids and can expedite the aggregation of Aβ through seeding. Here, we advance the understanding of Aα biophysics and biology in several important ways. We report the first cryogenic electron microscopy (cryo-EM) structure of an Aα amyloid fibril, proving unambiguously that the peptide is fibrillogenic. We demonstrate that Aα induces Aβ to form amyloid aggregates that are less toxic than pure Aβ aggregates and use nuclear magnetic resonance spectroscopy (NMR) to provide insights into specific interactions between Aα and Aβ in solution. This is the first evidence that Aα can coassemble with Aβ and alter its biological effects at relatively low concentrations. Based on the above, we urge researchers in the field to re-examine the significance of Aα in AD.

Structural polymorphism of amyloid fibrils in ATTR amyloidosis revealed by cryo-electron microscopy

ATTR amyloidosis is caused by the deposition of transthyretin in the form of amyloid fibrils in virtually every organ of the body, including the heart. This systemic deposition leads to a phenotypic variability that has not been molecularly explained yet. In brain amyloid conditions, previous studies suggest an association between clinical phenotype and the molecular structures of their amyloid fibrils. Here we investigate whether there is such an association in ATTRv amyloidosis patients carrying the mutation I84S. Using cryo-electron microscopy, we determined the structures of cardiac fibrils extracted from three ATTR amyloidosis patients carrying the ATTRv-I84S mutation, associated with a consistent clinical phenotype. We found that in each ATTRv-I84S patient, the cardiac fibrils exhibited different local conformations, and these variations can co-exist within the same fibril. Our finding suggests that one amyloid disease may associate with multiple fibril structures in systemic amyloidoses, calling for further studies.

Variant of uncertain significance Arg866Cys enhances disorderedness of h-BRCA1 (759-1064) region

High structural flexibility has been reported in the central region of BRCA1, which hinders the structural and functional evaluations of mutations identified in the domain. Additionally, the need to categorize variants of unknown significance (VUS) has increased due to the growth in the number of variants reported in clinical settings. Therefore, unraveling the disease-causing mechanism of VUS identified in different functional domains of BRCA1 is still challenging. The current study uses a multidisciplinary approach to assess the structural impact of BRCA1 Arg866Cys mutation discovered in the central domain of BRCA1. The structural alterations have been characterized using Circular-Dichroism spectroscopy, nano-DSF, and molecular-dynamics simulations. BRCA1 Arg866Cys mutant demonstrated more flexibility and lesser affinity to DNA than the wild-type protein. The BRCA1(759–1064) wild-type protein was shown to be a βII-rich protein with an induced D-O transition in the presence of DNA and 2,2,2-Trifluoroethanol (TFE). The protein's alpha-helical composition did not significantly change in the presence of TFE, besides an increase in β-turns and loops. Under Transmission Electron Microscopes (TEM), amyloid-like fibrils structure was detected for Arg866Cys mutant whereas the wild-type protein showed amorphous aggregates. An increased ThT fluorescence indicated β-rich composition and aggregation-prone behaviour for BRCA1 wild-type protein, while the fluorescence intensity was significantly quenched in the Arg866Cys mutant. Furthermore, increased conformational flexibility in the Arg866Cys variant was observed by principal component analysis. This work aims to comprehend the inherently disordered region of BRCA1 as well as the impact of missense mutations on folding patterns and binding to DNA for functional aspects.

Photocontrol of the β-Hairpin Polypeptide Structure through an Optimized Azobenzene-Based Amino Acid Analogue.

A family of neurodegenerative diseases, including Huntington's disease (HD) and spinocerebellar ataxias, are associated with an abnormal polyglutamine (polyQ) expansion in mutant proteins that become prone to form amyloid-like aggregates. Prior studies have suggested a key role for β-hairpin formation as a driver of nucleation and aggregation, but direct experimental studies have been challenging. Toward such research, we set out to enable spatiotemporal control over β-hairpin formation by the introduction of a photosensitive β-turn mimic in the polypeptide backbone, consisting of a newly designed azobenzene derivative. The reported derivative overcomes the limitations of prior approaches associated with poor photochemical properties and imperfect structural compatibility with the desired β-turn structure. A new azobenzene-based β-turn mimic was designed, synthesized, and found to display improved photochemical properties, both prior and after incorporation into the backbone of a polyQ polypeptide. The two isomers of the azobenzene-polyQ peptide showed different aggregate structures of the polyQ peptide fibrils, as demonstrated by electron microscopy and solid-state NMR (ssNMR). Notably, only peptides in which the β-turn structure was stabilized (azobenzene in the cis configuration) closely reproduced the spectral fingerprints of toxic, β-hairpin-containing fibrils formed by mutant huntingtin protein fragments implicated in HD. These approaches and findings will enable better deciphering of the roles of β-hairpin structures in protein aggregation processes in HD and other amyloid-related neurodegenerative diseases.

Cryo-EM observation of the amyloid key structure of polymorphic TDP-43 amyloid fibrils

The transactive response DNA-binding protein-43 (TDP-43) is a multi-facet protein involved in phase separation, RNA-binding, and alternative splicing. In the context of neurodegenerative diseases, abnormal aggregation of TDP-43 has been linked to amyotrophic lateral sclerosis and frontotemporal lobar degeneration through the aggregation of its C-terminal domain. Here, we report a cryo-electron microscopy (cryo-EM)-based structural characterization of TDP-43 fibrils obtained from the full-length protein. We find that the fibrils are polymorphic and contain three different amyloid structures. The structures differ in the number and relative orientation of the protofilaments, although they share a similar fold containing an amyloid key motif. The observed fibril structures differ from previously described conformations of TDP-43 fibrils and help to better understand the structural landscape of the amyloid fibril structures derived from this protein.

Insights into role of synergistic interplay among collagen type I, collagen type II, and water on the structure and nanomechanics of collagen fibrils in annulus fibrosus: a molecular dynamics study

ABSTRACT Annulus Fibrosus’s (AF) multi-directional load-bearing ability manifests from Nature’s design wherein type I collagen (COL-I) dominates outer AF and type II collagen (COL-II) dominates inner AF with increase in proteoglycan and water concentration. This indicates a synergistic chemo-mechanical interplay among constituents, contributing towards AF’s load-bearing nature. Present work investigates the interplay among COL-I, COL-II and water, and their role in AF collagen fibril nanomechanics using molecular dynamics simulations. Consequently, atomistic models of collagen microfibrils are constructed for four lamellar regions from outer to inner AF, by increasing COL-II and water concentration from 0% to 75%, and 65% to 75%. Results show an increase in local hydration around COL-II component and increase in intermolecular separation (21 Å to 23 Å), with increase in COL-II and water concentration towards inner AF. A combined increase in local hydration and intermolecular separation enhances intermolecular sliding – contributing to a reduction in tensile modulus from 2.1 to 1.6 GPa. Reduction in microfibril tensile modulus towards inner AF contributes to reduction in tensile modulus of AF lamellae towards inner AF, as reported in literature. Furthermore, increase in COL-II and water concentration shifts compressive behaviour from buckling to non-buckling dominant – enhancing collagen fibrils’ mechanical stability towards inner AF.

Insights into the Structural Basis of Amyloid Resistance Provided by Cryo-EM Structures of AApoAII Amyloid Fibrils

Amyloid resistance is the inability or the reduced susceptibility of an organism to develop amyloidosis. In this study we have analysed the molecular basis of the resistance to systemic AApoAII amyloidosis, which arises from the formation of amyloid fibrils from apolipoprotein A-II (ApoA-II). The disease affects humans and animals, including SAMR1C mice that express the C allele of ApoA-II protein, whereas other mouse strains are resistant to development of amyloidosis due to the expression of other ApoA-II alleles, such as ApoA-IIF. Using cryo-electron microscopy, molecular dynamics simulations and other methods, we have determined the structures of pathogenic AApoAII amyloid fibrils from SAMR1C mice and analysed the structural effects of ApoA-IIF-specific mutational changes. Our data show that these changes render ApoA-IIF incompatible with the specific fibril morphologies, with which ApoA-II protein can become pathogenic in vivo.

Phospholipids and Cholesterol Determine Molecular Mechanisms of Cytotoxicity of α-Synuclein Oligomers and Fibrils.

Progressive loss of dopaminergic (DA) neurons in the substantia nigra pars compacta, hypothalamus, and thalamus is a hallmark of Parkinson's disease. Neuronal death is linked to the abrupt aggregation of α-synuclein (α-Syn), a small membrane protein that regulates cell vesicle trafficking. α-Syn aggregation rate, as well as the secondary structure and toxicity of α-Syn fibrils, could be uniquely altered by lipids. However, molecular mechanisms that determine such a remarkable difference in the toxicity of α-Syn fibrils formed in the presence of lipids remain unclear. In this study, we used a set of molecular assays to determine the molecular mechanism by which α-Syn fibrils formed in the presence of phosphatidylcholine (PC), cardiolipin (CL), and cholesterol (Cho) exert cell toxicity. We found that rat dopaminergic cells exposed to α-Syn fibrils formed in the presence of different lipids exert drastically different magnitudes and dynamics of unfolded protein response (UPR) in the endoplasmic reticulum (ER) and mitochondria (MT). Specifically, α-Syn:CL were found to cause the strongest, whereas α-Syn fibrils formed in the absence of lipids had the lowest magnitude of the UPR cell response. We also found the opposite dynamics of the ER- and MT-UPR responses in rat dopaminergic cells exposed to protein aggregates. These results could suggest that facing severe ER stress, dopaminergic cells suppress MT-UPR response, enabling the maximal ATP production to restore their normal physiological function. These findings help to better understand complex mechanisms of cell toxicity of amyloid aggregates and ultimately find neuroprotective drug candidates that will be able to suppress the spread of Parkinson's disease.

A pilot study for decellularizing human and porcine cornea for future use in corneal regeneration

Purpose: To effectively decellularize human and porcine corneas for future use in corneal regeneration by using an already established decellularization technique being efficient in decellularizing blood vessels.Methods: One human and 4 porcine corneas were decellularized by using various washing steps with 3‐[(3‐cholamidopropyl) dimethylammonio]‐1‐propanesulfonate (CHAPS) detergent, Benzonase, Ethylenediaminetetraacetic acid (EDTA), 5% Dextran or 5% D‐Mannitol. The quality of the decellularization process was assessed by quantitative and qualitative measurement of DNA content, glycosaminoglycans (GAGs), immunofluorescent staining for Collagen I, V and keratocan, and Transmission Electron Microscopy (TEM) to observe the structure of the collagen fibrils was used.Results: The decellularization process showed 99,94% and 99,52% DNA content reduction in the human and porcine corneas when using Dextran, respectively, while more DNA remained in the porcine corneas when D‐Mannitol was used. Similar pattern was observed in the preservation of GAGs, with the highest amount being found in the human cornea, and less in the porcine corneas. H&amp;E and Immunofluorescent staining showed no presence of cell nuclei when compared to the control native corneas, while Alcian blue staining qualitatively confirmed the presence of GAGs. Collagen I, V and keratocan were still present in the decellularized corneas when compared to the native ones, while TEM microscopy further confirmed the similar patterns of the collagen fibrils in the decellularized‐, compared to the native‐ corneas.Conclusions: This pilot study showed that our decellularization method is effective in decellularizing human and porcine corneas, with very high amount of DNA being removed from the corneas, while the GAGs were preserved to an acceptable extent, and the structure and pattern of the collagen fibrils maintained.

Molecular basis for non-invasive diagnostics of cardiac amyloids using bone tracers.

Amyloid diseases including Alzheimer's, Parkinson's and over 30 others are incurable life-threatening disorders caused by abnormal protein deposition as fibrils in various organs. Cardiac amyloidosis is particularly challenging to diagnose and treat. Identification of the fibril-forming protein, which in the heart is usually amyloid transthyretin (ATTR) or amyloid immunoglobulin light chain (AL), is paramount to treatment. A transformative non-invasive diagnostic modality is imaging using technetium-labeled pyrophosphate or diphosphonate bone tracers, 99mTc-PYP/DPD/HMDP. For unknown reasons, these tracers show preferential uptake by ATTR deposits. The tracer-binding moiety is unknown and potentially involves amyloid fibrils and/or amyloid-associated calcific deposits. We propose that, like in the bone, the tracers chelate to surface-bound Ca2+ in amyloid. In high-affinity protein sites, Ca2+ is coordinated by pairs of acidic residues. To identify such residues on amyloids, we harnessed atomic structures of patient-derived cardiac amyloids determined using cryogenic electron microscopy since 2019. These structures help explain why most but not all ATTR deposits uptake 99mTc-PYP/DPD/HMDP radiotracers, while in AL the opposite is true. Moreover, fibril structures help explain greater microcalcification observed in ATTR vs. AL deposits. These findings may aid the diagnostics and therapeutic targeting of cardiac amyloidosis and are relevant to other amyloids.

Amyloid fibril cytotoxicity and associated disorders.

Misfolded proteins assemble into fibril structures that are called amyloids. Unlike usually folded proteins, misfolded fibrils are insoluble and deposit extracellularly or intracellularly. Misfolded proteins interrupt the function and structure of cells and cause amyloid disease. There is increasing evidence that the most pernicious species are oligomers. Misfolded proteins disrupt cell function and cause cytotoxicity by calcium imbalance, mitochondrial dysfunction, and intracellular reactive oxygen species. Despite profound impacts on health, social, and economic factors, amyloid diseases remain untreatable. To develop new therapeutics and to understand the pathological manifestations of amyloidosis, research into the origin and pathology of amyloidosis is urgently needed. This chapter describes the basic concept of amyloid disease and the function of atypical amyloid deposits in them.

A β-barrel-like tetramer formed by a β-hairpin derived from Aβ.

β-Hairpins formed by the β-amyloid peptide Aβ are building blocks of Aβ oligomers. Three different alignments of β-hairpins have been observed in the structures of Aβ oligomers or fibrils. Differences in β-hairpin alignment likely contribute to the heterogeneity of Aβ oligomers and thus impede their study at high-resolution. Here, we designed, synthesized, and studied a series of β-hairpin peptides derived from Aβ12-40 in one of these three alignments and investigated their solution-phase assembly and folding. These assays reveal the formation of tetramers and octamers that are stabilized by intermolecular hydrogen bonding interactions between Aβ residues 12-14 and 38-40 as part of an extended β-hairpin conformation. X-ray crystallographic studies of one peptide from this series reveal the formation of β-barrel-like tetramers and octamers that are stabilized by edge-to-edge hydrogen bonding and hydrophobic packing. Dye-leakage and caspase 3/7 activation assays using tetramer and octamer forming peptides from this series reveal membrane-damaging and apoptotic properties. A molecular dynamics simulation of the β-barrel-like tetramer embedded in a lipid bilayer shows membrane disruption and water permeation. The tetramers and octamers described herein provide additional models of how Aβ may assemble into oligomers and supports the hypothesis that β-hairpin alignment and topology may contribute directly to oligomer heterogeneity.

Copper binding alters the core structure of amyloid fibrils formed by Y145Stop human prion protein.

Transmissible spongiform encephalopathies (or prion diseases) such as Creutzfeldt-Jacob disease, mad cow disease, and scrapie are characterized by accumulation in the brain of misfolded prion protein aggregates (PrPSc) that have properties of amyloid fibrils. Given that transition metal ions, such as copper and zinc, appear to be important for physiological functions of cellular PrP (PrPC) as well as for prion disease pathogenesis, exploring their role in the protein aggregation process is of considerable interest. Copper(II) in particular is well-known to bind to the four tandem octapeptide repeats (PHGGGWGQ) located in the N-terminal region of PrP (human PrP amino acids 60-91), as well as to additional histidine binding sites outside the octarepeat region with distinct binding modes depending on Cu2+ concentration. Here, using the Y145Stop human prion protein variant (huPrP23-144) as a model and a combination of multidimensional solution and solid-state NMR spectroscopy, atomic force microscopy and thioflavin T fluorescence assays we probed the binding of Cu2+ to monomeric huPrP23-144 and the impact of this binding on fibril assembly kinetics and their structural properties. Remarkably, we found that fibrils formed by huPrP23-144 containing one molar equivalent of bound Cu2+ adopt a core structure that is distinct from that found for huPrP23-144 in the absence of Cu2+ but, instead, corresponds to a conformational strain formed by huPrP23-144 containing the A117V mutation. A similar huPrP23-144 A117V-like amyloid core structure was adopted by a Cu2+-bound Δ51-91 huPrP23-144 deletion variant lacking the entire octarepeat region, suggesting that Cu2+ binding to His residues 96, 111 and 140 located near the C-terminus of huPrP23-144 is primarily responsible for the observed change in fibril conformation, potentially due to partial structuring of the intrinsically disordered huPrP23-144 by the bound Cu2+ during the fibril assembly process. We also found that fibrils formed by Cu2+-bound huPrP23-144 adopt the native huPrP23-144-like rather than A117V-like structure when the fibrillization reaction is seeded with pre-formed huPrP23-144 amyloid.

Morphological features and types of aggregated structures.

In vivo, protein aggregation arises due to incorrect folding or misfolding. The aggregation of proteins into amyloid fibrils is the characteristic feature of various misfolding diseases known as amyloidosis, such as Alzheimer's and Parkinson's disease. The heterogeneous nature of these fibrils restricts the extent to which their structure may be characterized. Advancements in techniques, such as X-ray diffraction, cryo-electron microscopy, and solid-state NMR have yielded intricate insights into structures of different amyloid fibrils. These studies have unveiled a diverse range of polymorphic structures that typically conform to the cross-β amyloid pattern. This chapter provides a concise overview of the information acquired in the field of protein aggregation, with particular focus on amyloids.