scholarly journals Prediction of Transmembrane Regions, Cholesterol, and Ganglioside Binding Sites in Amyloid-Forming Proteins Indicate Potential for Amyloid Pore Formation

2021 ◽  
Vol 14 ◽  
Author(s):  
Katja Venko ◽  
Marjana Novič ◽  
Veronika Stoka ◽  
Eva Žerovnik
Keyword(s):  
Pore Formation ◽  
Amyloid Fibrils ◽  
Common Source ◽  
Binding Motifs ◽  
Amyloid Toxicity ◽  
Transmembrane Channels ◽  
Open Issue ◽  
Ion Conducting ◽  
Functional Amyloids ◽  
Key Events

Besides amyloid fibrils, amyloid pores (APs) represent another mechanism of amyloid induced toxicity. Since hypothesis put forward by Arispe and collegues in 1993 that amyloid-beta makes ion-conducting channels and that Alzheimer's disease may be due to the toxic effect of these channels, many studies have confirmed that APs are formed by prefibrillar oligomers of amyloidogenic proteins and are a common source of cytotoxicity. The mechanism of pore formation is still not well-understood and the structure and imaging of APs in living cells remains an open issue. To get closer to understand AP formation we used predictive methods to assess the propensity of a set of 30 amyloid-forming proteins (AFPs) to form transmembrane channels. A range of amino-acid sequence tools were applied to predict AP domains of AFPs, and provided context on future experiments that are needed in order to contribute toward a deeper understanding of amyloid toxicity. In a set of 30 AFPs we predicted their amyloidogenic propensity, presence of transmembrane (TM) regions, and cholesterol (CBM) and ganglioside binding motifs (GBM), to which the oligomers likely bind. Noteworthy, all pathological AFPs share the presence of TM, CBM, and GBM regions, whereas the functional amyloids seem to show just one of these regions. For comparative purposes, we also analyzed a few examples of amyloid proteins that behave as biologically non-relevant AFPs. Based on the known experimental data on the β-amyloid and α-synuclein pore formation, we suggest that many AFPs have the potential for pore formation. Oligomerization and α-TM helix to β-TM strands transition on lipid rafts seem to be the common key events.

scholarly journals Current Understanding of the Structure, Stability and Dynamic Properties of Amyloid Fibrils

2021 ◽  
Vol 22 (9) ◽  
pp. 4349
Author(s):  
Eri Chatani ◽  
Keisuke Yuzu ◽  
Yumiko Ohhashi ◽  
Yuji Goto
Keyword(s):  
Amyloid Fibrils ◽  
Polypeptide Chain ◽  
Dynamic Properties ◽  
Protein Molecule ◽  
Side Chain ◽  
Structure Stability ◽  
Side Chains ◽  
Precise Control ◽  
Functional Amyloids ◽  
Structural Architecture

Amyloid fibrils are supramolecular protein assemblies represented by a cross-β structure and fibrous morphology, whose structural architecture has been previously investigated. While amyloid fibrils are basically a main-chain-dominated structure consisting of a backbone of hydrogen bonds, side-chain interactions also play an important role in determining their detailed structures and physicochemical properties. In amyloid fibrils comprising short peptide segments, a steric zipper where a pair of β-sheets with side chains interdigitate tightly is found as a fundamental motif. In amyloid fibrils comprising longer polypeptides, each polypeptide chain folds into a planar structure composed of several β-strands linked by turns or loops, and the steric zippers are formed locally to stabilize the structure. Multiple segments capable of forming steric zippers are contained within a single protein molecule in many cases, and polymorphism appears as a result of the diverse regions and counterparts of the steric zippers. Furthermore, the β-solenoid structure, where the polypeptide chain folds in a solenoid shape with side chains packed inside, is recognized as another important amyloid motif. While side-chain interactions are primarily achieved by non-polar residues in disease-related amyloid fibrils, the participation of hydrophilic and charged residues is prominent in functional amyloids, which often leads to spatiotemporally controlled fibrillation, high reversibility, and the formation of labile amyloids with kinked backbone topology. Achieving precise control of the side-chain interactions within amyloid structures will open up a new horizon for designing useful amyloid-based nanomaterials.

scholarly journals Protein Co-Aggregation Related to Amyloids: Methods of Investigation, Diversity, and Classification

2018 ◽  
Vol 19 (8) ◽  
pp. 2292 ◽  
Author(s):  
Stanislav Bondarev ◽  
Kirill Antonets ◽  
Andrey Kajava ◽  
Anton Nizhnikov ◽  
Galina Zhouravleva
Keyword(s):  
Binding Site ◽  
Molecular Mechanisms ◽  
Amyloid Fibrils ◽  
Specific Binding ◽  
Protein S ◽  
Functional Protein ◽  
Functional Roles ◽  
Protein Fibrils ◽  
Protein Functions ◽  
Functional Amyloids

Amyloids are unbranched protein fibrils with a characteristic spatial structure. Although the amyloids were first described as protein deposits that are associated with the diseases, today it is becoming clear that these protein fibrils play multiple biological roles that are essential for different organisms, from archaea and bacteria to humans. The appearance of amyloid, first of all, causes changes in the intracellular quantity of the corresponding soluble protein(s), and at the same time the aggregate can include other proteins due to different molecular mechanisms. The co-aggregation may have different consequences even though usually this process leads to the depletion of a functional protein that may be associated with different diseases. The protein co-aggregation that is related to functional amyloids may mediate important biological processes and change of protein functions. In this review, we survey the known examples of the amyloid-related co-aggregation of proteins, discuss their pathogenic and functional roles, and analyze methods of their studies from bacteria and yeast to mammals. Such analysis allow for us to propose the following co-aggregation classes: (i) titration: deposition of soluble proteins on the amyloids formed by their functional partners, with such interactions mediated by a specific binding site; (ii) sequestration: interaction of amyloids with certain proteins lacking a specific binding site; (iii) axial co-aggregation of different proteins within the same amyloid fibril; and, (iv) lateral co-aggregation of amyloid fibrils, each formed by different proteins.

scholarly journals Modulating functional amyloid formation via alternative splicing of the premelanosomal protein PMEL17

2020 ◽  
Vol 295 (21) ◽  
pp. 7544-7553 ◽  
Author(s):  
Dexter N. Dean ◽  
Jennifer C. Lee
Keyword(s):  
Alternative Splicing ◽  
Amyloid Fibrils ◽  
Limited Proteolysis ◽  
Amyloid Formation ◽  
Functional Amyloid ◽  
Melanin Biosynthesis ◽  
Functional Amyloids ◽  
Fibril Morphology ◽  
Amyloid Assembly ◽  
Β Sheet

The premelanosomal protein (PMEL17) forms functional amyloid fibrils involved in melanin biosynthesis. Multiple PMEL17 isoforms are produced, two of which arise from excision of a cryptic intron within the amyloid-forming repeat (RPT) domain, leading to long (lRPT) and short (sRPT) isoforms with 10 and 7 imperfect repeats, respectively. Both lRPT and sRPT isoforms undergo similar pH-dependent mechanisms of amyloid formation and fibril dissolution. Here, using human PMEL17, we tested the hypothesis that the minor, but more aggregation-prone, sRPT facilitates amyloid formation of lRPT. We observed that cross-seeding by sRPT fibrils accelerates the rate of lRPT aggregation, resulting in propagation of an sRPT-like twisted fibril morphology, unlike the rodlike structure that lRPT normally adopts. This templating was specific, as the reversed reaction inhibited sRPT fibril formation. Despite displaying ultrastructural differences, self- and cross-seeded lRPT fibrils had a similar β-sheet structured core, revealed by Raman spectroscopy, limited-proteolysis, and fibril disaggregation experiments, suggesting the fibril twist is modulated by N-terminal residues outside the amyloid core. Interestingly, bioinformatics analysis of PMEL17 homologs from other mammals uncovered that long and short RPT isoforms are conserved among members of this phylogenetic group. Collectively, our results indicate that the short isoform of RPT serves as a “nucleator” of PMEL17 functional amyloid formation, mirroring how bacterial functional amyloids assemble during biofilm formation. Whereas bacteria regulate amyloid assembly by using individual genes within the same operon, we propose that the modulation of functional amyloid formation in higher organisms can be accomplished through alternative splicing.

scholarly journals pH-induced molecular shedding drives the formation of amyloid fibril-derived oligomers

2015 ◽  
Vol 112 (18) ◽  
pp. 5691-5696 ◽  
Author(s):  
Kevin W. Tipping ◽  
Theodoros K. Karamanos ◽  
Toral Jakhria ◽  
Matthew G. Iadanza ◽  
Sophia C. Goodchild ◽  
...  
Keyword(s):  
Amyloid Fibrils ◽  
Correlation Spectroscopy ◽  
Synthetic Membranes ◽  
Fluorescence Correlation ◽  
Amyloid Toxicity ◽  
Tht Fluorescence ◽  
Amyloid Aggregates ◽  
Key Factor ◽  
Cellular Dysfunction ◽  
Acidic Compartments

Amyloid disorders cause debilitating illnesses through the formation of toxic protein aggregates. The mechanisms of amyloid toxicity and the nature of species responsible for mediating cellular dysfunction remain unclear. Here, using β2-microglobulin (β2m) as a model system, we show that the disruption of membranes by amyloid fibrils is caused by the molecular shedding of membrane-active oligomers in a process that is dependent on pH. Using thioflavin T (ThT) fluorescence, NMR, EM and fluorescence correlation spectroscopy (FCS), we show that fibril disassembly at pH 6.4 results in the formation of nonnative spherical oligomers that disrupt synthetic membranes. By contrast, fibril dissociation at pH 7.4 results in the formation of nontoxic, native monomers. Chemical cross-linking or interaction with hsp70 increases the kinetic stability of fibrils and decreases their capacity to cause membrane disruption and cellular dysfunction. The results demonstrate how pH can modulate the deleterious effects of preformed amyloid aggregates and suggest why endocytic trafficking through acidic compartments may be a key factor in amyloid disease.

scholarly journals Amyloid conformers of the FXR1 protein prevent mRNA degradation in cortical neurons

2019 ◽  
Author(s):  
J.V. Sopova ◽  
E. I Koshel ◽  
T.A. Belashova ◽  
S.P. Zadorsky ◽  
A.V. Sergeeva ◽  
...  
Keyword(s):  
Cortical Neurons ◽  
Large Scale ◽  
Amyloid Fibrils ◽  
Mammalian Species ◽  
Rnase A ◽  
Mammalian Brain ◽  
Polarization Microscopy ◽  
Proteomic Approach ◽  
Functional Amyloids

AbstractFunctional amyloids regulate vital processes in a variety of organisms from bacteria to higher eukaryotes. The development of methods enabling large-scale screening for amyloids opens up opportunity for systemic analysis of the prevalence of amyloids in nature. Using an original proteomic approach, we identified several proteins forming amyloid-like detergent-resistant aggregates in the rat brain. One of them is the FXR1 protein, which is known to regulate memory and emotions (1, 2). We demonstrated that in brain FXR1 forms amyloid oligomers and insoluble detergent-resistant aggregates that strongly colocalize with amyloid-specific dye Thioflavin S and bind mRNA molecules. Moreover, we demonstrated that mRNAs colocalized with FXR1 amyloid particles are completely resistant to treatment with RNAse A. Taking into consideration that the members of ribonuclease A superfamily function in neurons (3) we can conclude that amyloid conformers of FXR1 control RNA stability in brain. Thus, in contrast to pathological amyloids that cause neurodegeneration, FXR1 is the functional amyloid in forebrain. We showed that amyloid properties of FXR1 depend on its N-terminal part from 1 to 379 amino acids. This fragment forms amyloid fibrils in vitro that bind Congo red and manifest apple-green birefringence when assayed by polarization microscopy. The amyloid-forming region of FXR1 is highly conserved in mammals. These data suggest that the ability of amyloid conformers of FXR1 to protect mRNAs is characteristic of different mammalian species, including humans.Significance StatementAmyloids are highly ordered cross-β sheet protein fibrils associated with many neurodegenerative diseases including Alzheimer’s disease. However, some amyloid proteins regulate vital processes. We identified a set of proteins that form amyloid-like aggregates in the brain of healthy rats. One of them - the FXR1 protein is known to regulate memory and emotions. FXR1 forms amyloid fibrils that bind RNA molecules and prevent their degradation in brain cortex neurons. Amyloid-forming sequence of FXR1 is highly conserved across mammals including human. Discovery of functional amyloids in mammalian brain shows that strategy aimed at the development of universal anti-amyloid drugs is unpromising. Such potential drugs should prevent or suppress formation of pathological aggregates of a certain protein, but not affect functional amyloids.

Amyloid toxicity in Alzheimer’s disease

2018 ◽  
Vol 29 (6) ◽  
pp. 613-627 ◽  
Author(s):  
Allison B. Reiss ◽  
Hirra A. Arain ◽  
Mark M. Stecker ◽  
Nicolle M. Siegart ◽  
Lora J. Kasselman
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Pore Formation ◽  
Amyloid Β ◽  
Precursor Protein ◽  
Calcium Balance ◽  
Aβ Oligomers ◽  
Synaptic Loss ◽  
Amyloid Toxicity ◽  
Aβ Production

Abstract A major feature of Alzheimer’s disease (AD) pathology is the plaque composed of aggregated amyloid-β (Aβ) peptide. Although these plaques may have harmful properties, there is much evidence to implicate soluble oligomeric Aβ as the primary noxious form. Aβ oligomers can be generated both extracellularly and intracellularly. Aβ is toxic to neurons in a myriad of ways. It can cause pore formation resulting in the leakage of ions, disruption of cellular calcium balance, and loss of membrane potential. It can promote apoptosis, cause synaptic loss, and disrupt the cytoskeleton. Current treatments for AD are limited and palliative. Much research and effort is being devoted to reducing Aβ production as an approach to slowing or preventing the development of AD. Aβ formation results from the amyloidogenic cleavage of human amyloid precursor protein (APP). Reconfiguring this process to disfavor amyloid generation might be possible through the reduction of APP or inhibition of enzymes that convert the precursor protein to amyloid.

scholarly journals The AWSEM-Amylometer: predicting amyloid propensity and fibril topology using an optimized folding landscape model

2017 ◽  
Author(s):  
Mingchen Chen ◽  
Nicholas P Schafer ◽  
Weihua Zheng ◽  
Peter G Wolynes
Keyword(s):  
Amyloid Fibrils ◽  
Protein Sequences ◽  
Landscape Model ◽  
Fiber Structure ◽  
Multiple Datasets ◽  
Folding Simulation ◽  
Relative Arrangement ◽  
Free Energy Landscapes ◽  
Amyloidogenic Peptides ◽  
Functional Amyloids

AbstractAmyloids are fibrillar protein aggregates with simple repeated structural motifs in their cores, usually β-strands but sometimes α-helices. Identifying the amyloid-prone regions within protein sequences is important both for understanding the mechanisms of amyloid-associated diseases and for understanding functional amyloids. Based on the crystal structures of seven cross-β amyloidogenic peptides with different topologies and one recently solved cross-α fiber structure, we have developed a computational approach for identifying amyloidogenic segments in protein sequences using the Associative memory, Water mediated, Structure and Energy Model. The AWSEM-Amylometer performs favorably in comparison with other predictors in predicting aggregation-prone sequences in multiple datasets. The method also predicts the specific topologies (the relative arrangement of β-strands in the core) of the amyloid fibrils well. An important advantage of the AWSEM-Amylometer over other existing methods is its direct connection with an efficient, optimized protein folding simulation model, AWSEM. This connection allows one to combine efficient and accurate search of protein sequences for amyloidogenic segments with the detailed study of the thermodynamic and kinetic roles that these segments play in folding and aggregation in the context of the entire protein sequence. We present new simulation results that highlight the free energy landscapes of peptides that can take on multiple fibril topologies. We also demonstrate how the Amylometer methodology can be straightforwardly extended to the study of functional amyloids that have the recently discovered cross-α fibril architecture.

Direct proof of the amyloid nature of yeast prions [PSI+] and [PIN+] by the method of immunoprecipitation of native fibrils

2021 ◽  
Vol 21 (6) ◽  
Author(s):  
Aleksandra V Sergeeva ◽  
Tatyana A Belashova ◽  
Stanislav A Bondarev ◽  
Marya E Velizhanina ◽  
Yury A Barbitoff ◽  
...  
Keyword(s):  
Congo Red ◽  
Amyloid Fibrils ◽  
Specific Binding ◽  
Polarized Light ◽  
Direct Proof ◽  
Indirect Evidence ◽  
Structural Features ◽  
Functional Amyloids ◽  
Red Dye

ABSTRACT Prions are proteins that can exist in several structurally and functionally distinct states, one or more of which is transmissible. Yeast proteins Sup35 and Rnq1 in prion state ([PSI+] and [PIN+], respectively) form oligomers and aggregates, which are transmitted from parents to offspring in a series of generations. Several pieces of indirect evidence indicate that these aggregates also possess amyloid properties, but their binding to amyloid-specific dyes has not been shown in vivo. Meanwhile, it is the specific binding to the Congo Red dye and birefringence in polarized light after such staining that is considered the gold standard for proving the amyloid properties of a protein. Here, we used immunoprecipitation to extract native fibrils of the Sup35 and Rnq1 proteins from yeast strains with different prion status. These fibrils are detected by electron microscopy, stained with Congo Red and exhibit yellow-green birefringence after such staining. All these data show that the Sup35 and Rnq1 proteins in prion state form amyloid fibrils in vivo. The technology of fibrils extraction in combination with standard cytological methods can be used to identify new pathological and functional amyloids in any organism and to analyze the structural features of native amyloid fibrils.

scholarly journals Looking Beyond the Core: The Role of Flanking Regions in the Aggregation of Amyloidogenic Peptides and Proteins

2020 ◽  
Vol 14 ◽  
Author(s):  
Sabine M. Ulamec ◽  
David J. Brockwell ◽  
Sheena E. Radford
Keyword(s):  
Amyloid Fibrils ◽  
Amyloid Β ◽  
Alpha Synuclein ◽  
Early Observation ◽  
Modulate Function ◽  
Target Disease ◽  
Chaperone Binding ◽  
Functional Amyloids ◽  
Flanking Regions

Amyloid proteins are involved in many neurodegenerative disorders such as Alzheimer’s disease [Tau, Amyloid β (Aβ)], Parkinson’s disease [alpha-synuclein (αSyn)], and amyotrophic lateral sclerosis (TDP-43). Driven by the early observation of the presence of ordered structure within amyloid fibrils and the potential to develop inhibitors of their formation, a major goal of the amyloid field has been to elucidate the structure of the amyloid fold at atomic resolution. This has now been achieved for a wide variety of sequences using solid-state NMR, microcrystallography, X-ray fiber diffraction and cryo-electron microscopy. These studies, together with in silico methods able to predict aggregation-prone regions (APRs) in protein sequences, have provided a wealth of information about the ordered fibril cores that comprise the amyloid fold. Structural and kinetic analyses have also shown that amyloidogenic proteins often contain less well-ordered sequences outside of the amyloid core (termed here as flanking regions) that modulate function, toxicity and/or aggregation rates. These flanking regions, which often form a dynamically disordered “fuzzy coat” around the fibril core, have been shown to play key parts in the physiological roles of functional amyloids, including the binding of RNA and in phase separation. They are also the mediators of chaperone binding and membrane binding/disruption in toxic amyloid assemblies. Here, we review the role of flanking regions in different proteins spanning both functional amyloid and amyloid in disease, in the context of their role in aggregation, toxicity and cellular (dys)function. Understanding the properties of these regions could provide new opportunities to target disease-related aggregation without disturbing critical biological functions.

AMYLOID: A NATURAL NANOMATERIAL

2011 ◽  
Vol 10 (04n05) ◽  
pp. 909-917 ◽  
Author(s):  
SAMIR K. MAJI
Keyword(s):  
Amyloid Fibrils ◽  
Prion Diseases ◽  
Skin Pigmentation ◽  
Pituitary Hormones ◽  
Secretory Cells ◽  
Temperature Changes ◽  
Amyloid A ◽  
Degradation Temperature ◽  
Enzyme Degradation ◽  
Functional Amyloids

Amyloids are stable, β-sheet-rich protein/peptides aggregates with 2–15 nm diameter and few micrometers long. It is originally associated with many human diseases such as Alzheimer's, Parkinson's and prion diseases. Amyloids are resistant to enzyme degradation, temperature changes and wide ranges of pH. Although, amyloids are hard and their stiffness is comparable to steel, a constant recycling of monomer occur inside the amyloid fibrils. It grows in a nucleation dependent polymerization manner by recruiting native soluble protein and by converting them to amyloid. These extraordinary physical properties make amyloids attractive for nanotechnological applications. Some amyloid fibrils have also evolved to perform native biological functions (functional amyloid) of the host organism. Functional amyloids are present in mammals such as amyloids of pMel17 and pituitary hormones, where they help in skin pigmentation and hormone storage, respectively. Here, the progress of utilizing amyloid fibrils for nanobiotechnological applications with particular emphasis on the recent studies that amyloid could be utilized for the formulation of peptide/protein drugs depot and how secretory cells uses amyloid for hormone storage will be reviewed.

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