scholarly journals Modulation of amyloid assembly by glycosaminoglycans: from mechanism to biological significance

2017 ◽  
Vol 95 (3) ◽  
pp. 329-337 ◽  
Author(s):  
Noé Quittot ◽  
Mathew Sebastiao ◽  
Steve Bourgault
Keyword(s):  
Self Assembly ◽  
Protein Misfolding ◽  
Amyloid Fibrils ◽  
Biological Significance ◽  
Active Research ◽  
Living Organisms ◽  
Functional Amyloids ◽  
Almost All ◽  
Misfolding Diseases ◽  
Amyloid Assembly

Glycosaminoglycans (GAGs) are long and unbranched polysaccharides that are abundant in the extracellular matrix and basement membrane of multicellular organisms. These linear polyanionic macromolecules are involved in many physiological functions from cell adhesion to cellular signaling. Interestingly, amyloid fibrils extracted from patients afflicted with protein misfolding diseases are virtually always associated with GAGs. Amyloid fibrils are highly organized nanostructures that have been historically associated with pathological states, such as Alzheimer’s disease and systemic amyloidoses. However, recent studies have identified functional amyloids that accomplish crucial physiological roles in almost all living organisms, from bacteria to insects and mammals. Over the last 2 decades, numerous reports have revealed that sulfated GAGs accelerate and (or) promote the self-assembly of a large diversity of proteins, both inherently amyloidogenic and non-aggregation prone. Despite the fact that many studies have investigated the molecular mechanism(s) by which GAGs induce amyloid assembly, the mechanistic elucidation of GAG-mediated amyloidogenesis still remains the subject of active research. In this review, we expose the contribution of GAGs in amyloid assembly, and we discuss the pathophysiological and functional significance of GAG-mediated fibrillization. Finally, we propose mechanistic models of the unique and potent ability of sulfated GAGs to hasten amyloid fibril formation.

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 Nanoimaging for Protein Misfolding Diseases. Critical Role of Misfolded Dimers in the Amyloid Self-Assembly

2011 ◽  
Vol 17 (S2) ◽  
pp. 170-171
Author(s):  
A Krasnoslobodtsev ◽  
B-H Kim ◽  
Y Lyubchenko
Keyword(s):  
Self Assembly ◽  
Protein Misfolding ◽  
Critical Role ◽  
Misfolding Diseases

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

scholarly journals The RHIM within the M45 protein from murine cytomegalovirus forms heteromeric amyloid fibrils with RIPK1 and RIPK3

2018 ◽  
Author(s):  
Chi L. L. Pham ◽  
Merryn Strange ◽  
Ailis O’ Carroll ◽  
Nirukshan Shanmugam ◽  
Emma Sierecki ◽  
...  
Keyword(s):  
Cell Death ◽  
Biological Activity ◽  
Self Assembly ◽  
Amyloid Fibrils ◽  
Human Cells ◽  
Terminal Region ◽  
Murine Cytomegalovirus ◽  
Homotypic Interaction ◽  
Amyloid Assembly

AbstractThe M45 protein from murine cytomegalovirus protects infected murine cells from death by necroptosis and can protect human cells from necroptosis induced by TNFR activation, when heterologously expressed. We show that the N-terminal 90 residues of the M45 protein, which contain a RIP Homotypic Interaction Motif (RHIM), are sufficient to confer protection against TNFR-induced necroptosis. This N-terminal region of M45 drives rapid self-assembly into homo-oligomeric amyloid fibrils and interacts with the RHIMs of human RIPK1 and RIPK3 kinases to form heteromeric amyloid fibrils in vitro. An intact RHIM core tetrad is required for the inhibition of cell death by M45 and we show that mutation of those key tetrad residues abolishes homo- and hetero-amyloid assembly by M45 in vitro, suggesting that the amyloidogenic nature of the M45 RHIM underlies its biological activity. Our results indicate that M45 mimics the interactions made by RIPK1 with RIPK3 in forming heteromeric amyloid structures.

scholarly journals Modulation of Amyloidogenic Protein Self-Assembly Using Tethered Small Molecules

2020 ◽  
Author(s):  
Emma Cawood ◽  
Nicolas Guthertz ◽  
Jessica Ebo ◽  
Theodoros Karamanos ◽  
Sheena E. Radford FRS ◽  
...  
Keyword(s):  
Protein Interactions ◽  
Structural Characterization ◽  
Self Assembly ◽  
Molecular Mechanisms ◽  
Amyloid Fibrils ◽  
Fibril Formation ◽  
X Ray Crystallography ◽  
Starting Point ◽  
Amyloid Assembly

<p></p><p>Protein-protein interactions (PPIs) are involved in many of life’s essential biological functions yet are also an underlying cause of several human diseases, including amyloidosis. The modulation of PPIs presents opportunities to gain mechanistic insights into amyloid assembly, particularly through the use of methods which can trap specific intermediates for detailed study. Such information can also provide a starting point for drug discovery. Here, we demonstrate that covalently tethered small molecule fragments can be used to stabilize specific oligomers during amyloid fibril formation, facilitating the structural characterization of these assembly intermediates. We exemplify the power of covalent tethering using the naturally occurring truncated variant (ΔN6) of the human protein β2-microglobulin (β2m), which assembles into amyloid fibrils associated with dialysis-related amyloidosis. Using this approach, we have trapped tetramers formed by ΔN6 under conditions which would normally lead to fibril formation and found that the degree of tetramer stabilization depends on the site of the covalent tether and the nature of the protein-fragment interaction. The covalent protein-ligand linkage enabled structural characterization of these trapped oligomeric species using X-ray crystallography and NMR, providing insight into why tetramer stabilization inhibits amyloid assembly. Our findings highlight the power of “post-translational chemical modification" as a tool to study biological molecular mechanisms. </p><br><p></p>

scholarly journals Microcin Amyloid Fibrils A Are Reservoir of Toxic Oligomeric Species

2012 ◽  
Vol 287 (15) ◽  
pp. 11665-11676 ◽  
Author(s):  
Mohammad Shahnawaz ◽  
Claudio Soto
Keyword(s):  
Environmental Conditions ◽  
Protein Misfolding ◽  
Amyloid Fibrils ◽  
Target Cells ◽  
Low Molecular Weight ◽  
Toxic Species ◽  
Soluble Species ◽  
Misfolding Diseases

Microcin E492 (Mcc), a low molecular weight bacteriocin produced by Klebsiella pneumoniae RYC492, has been shown to exist in two forms: soluble forms that are believed to be toxic to the bacterial cell by forming pores and non-toxic fibrillar forms that share similar biochemical and biophysical properties with amyloids associated with several human diseases. Here we report that fibrils polymerized in vitro from soluble forms sequester toxic species that can be released upon changing environmental conditions such as pH, ionic strength, and upon dilution. Our results indicate that basic pH (≥8.5), low NaCl concentrations (≤50 mm), and dilution (>10-fold) destabilize Mcc fibrils into more soluble species that are found to be toxic to the target cells. Additionally, we also found a similar conversion of non-toxic fibrils into highly toxic oligomers using Mcc aggregates produced in vivo. Moreover, the soluble protein released from fibrils is able to rapidly polymerize into amyloid fibrils under fibril-forming conditions and to efficiently seed aggregation of monomeric Mcc. Our findings indicate that fibrillar forms of Mcc constitute a reservoir of toxic oligomeric species that is released into the medium upon changing the environmental conditions. These findings may have substantial implications to understand the dynamic process of interconversion between toxic and non-toxic aggregated species implicated in protein misfolding diseases.

scholarly journals Exploring the sequence–structure relationship for amyloid peptides

2013 ◽  
Vol 450 (2) ◽  
pp. 275-283 ◽  
Author(s):  
Kyle L. Morris ◽  
Alison Rodger ◽  
Matthew R. Hicks ◽  
Maya Debulpaep ◽  
Joost Schymkowitz ◽  
...  
Keyword(s):  
Self Assembly ◽  
Amyloid Fibrils ◽  
Linear Dichroism ◽  
Model Systems ◽  
Molecular Architecture ◽  
Amyloid Peptides ◽  
Amyloid Fibril Formation ◽  
Structure Relationship ◽  
Fibre Diffraction ◽  
Misfolding Diseases

Amyloid fibril formation is associated with misfolding diseases, as well as fulfilling a functional role. The cross-β molecular architecture has been reported in increasing numbers of amyloid-like fibrillar systems. The Waltz algorithm is able to predict ordered self-assembly of amyloidogenic peptides by taking into account the residue type and position. This algorithm has expanded the amyloid sequence space, and in the present study we characterize the structures of amyloid-like fibrils formed by three peptides identified by Waltz that form fibrils but not crystals. The structural challenge is met by combining electron microscopy, linear dichroism, CD and X-ray fibre diffraction. We propose structures that reveal a cross-β conformation with ‘steric-zipper’ features, giving insights into the role for side chains in peptide packing and stability within fibrils. The amenity of these peptides to structural characterization makes them compelling model systems to use for understanding the relationship between sequence, self-assembly, stability and structure of amyloid fibrils.

Exploiting amyloid: how and why bacteria use cross-β fibrils

2012 ◽  
Vol 40 (4) ◽  
pp. 728-734 ◽  
Author(s):  
Elizabeth B. Sawyer ◽  
Dennis Claessen ◽  
Sally L. Gras ◽  
Sarah Perrett
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Protein Misfolding ◽  
Amyloid Fibrils ◽  
Streptomyces Coelicolor ◽  
Present Review ◽  
Protein Fibrils ◽  
Recent Developments ◽  
Misfolding Diseases

Many bacteria produce protein fibrils that are structurally analogous to those associated with protein misfolding diseases such as Alzheimer's disease. However, unlike fibrils associated with disease, bacterial amyloids have beneficial functions including conferring stability to biofilms, regulating development or imparting virulence. In the present review, we consider what makes amyloid fibrils so suitable for these roles and discuss recent developments in the study of bacterial amyloids, in particular the chaplins from Streptomyces coelicolor. We also consider the broader impact of the study of bacterial amyloids on our understanding of infection and disease and on developments in nanotechnology.

scholarly journals Dynamics of oligomer populations formed during the aggregation of Alzheimer’s Aβ42 peptide

2020 ◽  
Author(s):  
Thomas C. T. Michaels ◽  
Andela Šarić ◽  
Samo Curk ◽  
Katja Bernfur ◽  
Paolo Arosio ◽  
...  
Keyword(s):  
Protein Misfolding ◽  
Amyloid Fibrils ◽  
Amyloid Fibril ◽  
Fibril Formation ◽  
Therapeutic Interventions ◽  
Molecular Pathways ◽  
Amyloid Fibril Formation ◽  
Aβ42 Peptide ◽  
Heterogeneous Ensemble ◽  
Misfolding Diseases

AbstractOligomeric aggregates populated during the aggregation of the Aβ42 peptide have been identified as potent cytotoxins linked to Alzheimer’s disease, but the fundamental molecular pathways that control their dynamics have yet to be elucidated. By developing a general approach combining theory, experiment, and simulation, we reveal in molecular detail the mechanisms of Aβ42 oligomer dynamics during amyloid fibril formation. Even though all mature amyloid fibrils must originate as oligomers, we find that most Aβ42 oligomers dissociate to their monomeric precursors without forming new fibrils. Only a minority of oligomers converts into fibrillar species. Moreover, the heterogeneous ensemble of oligomeric species interconverts on timescales comparable to aggregation. Our results identify fundamentally new steps that could be targeted by therapeutic interventions designed to combat protein misfolding diseases.

scholarly journals Amyloid particles facilitate surface-catalyzed cross-seeding by acting as promiscuous nanoparticles

2020 ◽  
Author(s):  
Nadejda Koloteva-Levine ◽  
Ricardo Marchante ◽  
Tracey J. Purton ◽  
Jennifer R. Hiscock ◽  
Mick F. Tuite ◽  
...  
Keyword(s):  
Protein Misfolding ◽  
Full Range ◽  
Amyloid Formation ◽  
Surface Activities ◽  
Wide Range ◽  
Quantitative Characterisation ◽  
The Cross ◽  
Aβ42 Peptide ◽  
Misfolding Diseases ◽  
Amyloid Assembly

ABSTRACTAmyloid seeds are nanometre-sized protein particles that accelerate amyloid assembly, as well as propagate and transmit the amyloid protein conformation associated with a wide range of protein misfolding diseases. However, seeded amyloid growth through templated elongation at fibril ends cannot explain the full range of molecular behaviours observed during cross-seeded formation of amyloid by heterologous seeds. Here, we demonstrate that amyloid seeds can accelerate amyloid formation via a surface catalysis mechanism without propagating the specific amyloid conformation associated with the seeds. This type of seeding mechanism is demonstrated through quantitative characterisation of the cross-seeded assembly reactions involving two non-homologous and unrelated proteins: the human Aβ42 peptide and the yeast prion-forming protein Sup35NM. Our results suggest experimental approaches to differentiate seeding by templated elongation from non-templated amyloid seeding, and rationalise the molecular mechanism of the cross-seeding phenomenon as a manifestation of the aberrant surface activities presented by amyloid seeds as nanoparticles.

scholarly journals Physical Determinants of Amyloid Assembly in Biofilm Formation

mBio ◽  
2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Maria Andreasen ◽  
Georg Meisl ◽  
Jonathan D. Taylor ◽  
Thomas C. T. Michaels ◽  
Aviad Levin ◽  
...  
Keyword(s):  
Extracellular Matrix ◽  
Self Assembly ◽  
Biofilm Formation ◽  
Amyloid Fibrils ◽  
Environmental Stresses ◽  
Fibril Formation ◽  
Functional Amyloid ◽  
Content Type ◽  
Wide Range ◽  
Amyloid Assembly

ABSTRACTA wide range of bacterial pathogens have been shown to form biofilms, which significantly increase their resistance to environmental stresses, such as antibiotics, and are thus of central importance in the context of bacterial diseases. One of the major structural components of these bacterial biofilms are amyloid fibrils, yet the mechanism of fibril assembly and its importance for biofilm formation are currently not fully understood. By studying fibril formationin vitro, in a model system of two common but unrelated biofilm-forming proteins, FapC fromPseudomonas fluorescensand CsgA fromEscherichia coli, we found that the two proteins have a common aggregation mechanism. In both systems, fibril formation proceeds via nucleated growth of linear fibrils exhibiting similar measured rates of elongation, with negligible fibril self-replication. These similarities between two unrelated systems suggest that convergent evolution plays a key role in tuning the assembly kinetics of functional amyloid fibrils and indicates that only a narrow window of mechanisms and assembly rates allows for successful biofilm formation. Thus, the amyloid assembly reaction is likely to represent a means for controlling biofilm formation, both by the organism and by possible inhibitory drugs.IMPORTANCEBiofilms are generated by bacteria, embedded in the formed extracellular matrix. The biofilm's function is to improve the survival of a bacterial colony through, for example, increased resistance to antibiotics or other environmental stresses. Proteins secreted by the bacteria act as a major structural component of this extracellular matrix, as they self-assemble into highly stable amyloid fibrils, making the biofilm very difficult to degrade by physical and chemical means once formed. By studying the self-assembly mechanism of the fibrils from their monomeric precursors in two unrelated bacteria, our experimental and theoretical approaches shed light on the mechanism of functional amyloid assembly in the context of biofilm formation. Our results suggest that fibril formation may be a rate-limiting step in biofilm formation, which in turn has implications on the protein self-assembly reaction as a target for potential antibiotic drugs.

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