Amyloid-β forms fibrils by nucleated conformational conversion of oligomers

Lee, Jiyong; Culyba, Elizabeth K.; Powers, Evan T.; Kelly, Jeffery W.

doi:10.1038/nchembio.624

Cited by 355 publications

(448 citation statements)

References 51 publications

(76 reference statements)

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“…Schematic showing the overall reaction pathway and the corresponding rate constants identified in this paper. The approximate rates of the elongation-related processes have been identified in previous work (33,35,36).…”

Section: Methodsmentioning

confidence: 99%

“…The analysis of the kinetic data indicates that a major and continuous source of new fibrils under quiescent conditions is a secondary nucleation mechanism that involves both the monomeric peptide and mature amyloid fibrils. Because a large number of peptides are required to form ordered fibrillar forms that are detected in ThT measurements, aggregates generated through the secondary pathway must initially be in prefibrillar, oligomeric states that can escape detection by this method (24,35). To observe directly these ThT-invisible oligomer populations, which can ultimately convert to fibrils, and pinpoint their molecular origin, we studied a pair of samples with the same concentration of 35 Sradiolabeled peptide, but one containing in addition to the soluble radioactive peptide a small concentration of unlabeled preformed fibrils.…”

Section: Confirming the Source Of Oligomer Populations With Radioactivementioning

confidence: 99%

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Proliferation of amyloid-β42 aggregates occurs through a secondary nucleation mechanism

Cohen

Linse

Luheshi

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

1,214

128

1,843

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The generation of toxic oligomers during the aggregation of the amyloid-β (Aβ) peptide Aβ42 into amyloid fibrils and plaques has emerged as a central feature of the onset and progression of Alzheimer's disease, but the molecular pathways that control pathological aggregation have proved challenging to identify. Here, we use a combination of kinetic studies, selective radiolabeling experiments, and cell viability assays to detect directly the rates of formation of both fibrils and oligomers and the resulting cytotoxic effects. Our results show that once a small but critical concentration of amyloid fibrils has accumulated, the toxic oligomeric species are predominantly formed from monomeric peptide molecules through a fibril-catalyzed secondary nucleation reaction, rather than through a classical mechanism of homogeneous primary nucleation. This catalytic mechanism couples together the growth of insoluble amyloid fibrils and the generation of diffusible oligomeric aggregates that are implicated as neurotoxic agents in Alzheimer's disease. These results reveal that the aggregation of Aβ42 is promoted by a positive feedback loop that originates from the interactions between the monomeric and fibrillar forms of this peptide. Our findings bring together the main molecular species implicated in the Aβ aggregation cascade and suggest that perturbation of the secondary nucleation pathway identified in this study could be an effective strategy to control the proliferation of neurotoxic Aβ42 oligomers.

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Section: Methodsmentioning

confidence: 99%

Section: Confirming the Source Of Oligomer Populations With Radioactivementioning

confidence: 99%

Proliferation of amyloid-β42 aggregates occurs through a secondary nucleation mechanism

Cohen

Linse

Luheshi

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

1,214

128

1,843

View full text Add to dashboard Cite

show abstract

“…The model assumes a slow conversion of oligomers into fibrillar species, providing c o > c s . A finite concentration of suitably large oligomers is required to support a nucleated conformational conversion to generate a template for fibril elongation (24,25). In the model, the size of the smallest fibril-competent oligomer is denoted as i min .…”

Section: Comparative Kinetics Of Aggregation For Different Constructsmentioning

confidence: 99%

“…Even in the presence of flanking sequences the ratio c s c c remains greater than 1. As a result, in supersaturated solutions, the mechanisms are likely to always involve heterogeneities such as nonfibrillar oligomers (23,25) that form before or concomitantly with fibrils. It is possible that de novo sequence design can be used to generate sequence variants of Aβ for which c c < c s , as is the case with polyglutaminecontaining systems.…”

Section: N -K2 N -K2 and Ex1mentioning

confidence: 99%

Unmasking the roles of N- and C-terminal flanking sequences from exon 1 of huntingtin as modulators of polyglutamine aggregation

Crick

Ruff

Garai

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

203

274

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Huntington disease is caused by mutational expansion of the CAG trinucleotide within exon 1 of the huntingtin (Htt) gene. Exon 1 spanning N-terminal fragments (NTFs) of the Htt protein result from aberrant splicing of transcripts of mutant Htt. NTFs typically encompass a polyglutamine tract flanked by an N-terminal 17-residue amphipathic stretch (N17) and a C-terminal 38-residue proline-rich stretch (C38). We present results from in vitro biophysical studies that quantify the driving forces for and mechanisms of polyglutamine aggregation as modulated by N17 and C38. Although N17 is highly soluble by itself, it lowers the saturation concentration of soluble NTFs and increases the driving force, vis-à-vis homopolymeric polyglutamine, for forming insoluble aggregates. Kinetically, N17 accelerates fibril formation and destabilizes nonfibrillar intermediates. C38 is also highly soluble by itself, and it lends its high intrinsic solubility to lower the driving force for forming insoluble aggregates by increasing the saturation concentration of soluble NTFs. In NTFs with both modules, N17 and C38 act synergistically to destabilize nonfibrillar intermediates (N17 effect) and lower the driving force for forming insoluble aggregates (C38 effect). Morphological studies show that N17 and C38 promote the formation of ordered fibrils by NTFs. Homopolymeric polyglutamine forms a mixture of amorphous aggregates and fibrils, and its aggregation mechanisms involve early formation of heterogeneous distributions of nonfibrillar species. We propose that N17 and C38 act as gatekeepers that control the intrinsic heterogeneities of polyglutamine aggregation. This provides a biophysical explanation for the modulation of in vivo NTF toxicities by N17 and C38. (2). The Htt gene with expanded CAG tracts can undergo erroneous splicing, and the resultant aberrant messenger RNA is translated into a mutant exon 1 version of Htt that is similar to toxic NTFs found in neuronal intranuclear inclusions (3). Exon 1 spanning NTFs typically include a polyglutamine tract that is flanked on its N terminus by an amphipathic 17-residue stretch (MATLEKLMKAFESLKSF) denoted as N17 and by a 38-residue proline-rich stretch on its C terminus (P 11 -QLPQPPPQAQPLLPQPQ-P 10 ) denoted as C38. The N17 sequence is conserved among higher mammals (SI Appendix, Fig. S1), and mutations within N17 impact the properties of NTFs (4, 5). N17 enhances the overall rate of aggregation, as measured by the rate of forming large insoluble species both in vitro (6) and in yeast (7). The C-terminal proline-rich region of exon 1 modulates polyglutamine aggregation and reduces the cellular toxicity of Htt exon 1 even when the polyglutamine tract is significantly expanded (8, 9).A molecular-level understanding of the synergy between the length of polyglutamine tracts and its flanking sequences is essential for inferring the roles of N17 and C38 in vivo. This requires a quantitative understanding of the driving forces, mechanisms, and morphologies for homopolymeric polyglutamine and t...

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“…In recent single-molecule experiments [31][32][33][34] , an alternative two-step nucleation mechanism has been suggested: micellation of α-mers (monomers in the native soluble state) followed by a gradual conversion into β-mers within the dense micelle (Fig. 2).…”

Section: Introductionmentioning

confidence: 99%

Mechanisms and rates of nucleation of amyloid fibrils

Lee

Terentjev

2017

The Journal of Chemical Physics

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The classical nucleation theory finds the rate of nucleation proportional to the monomer concentration raised to the power, which is the 'critical nucleaus size', n c . The implicit assumption, that amyloids nucleate in the same way, has been recently challenged by an alternative two-step mechanism, when the soluble monomers first form a metastable aggregate (micelle), and then undergo conversion into the conformation rich in β-strands that are able to form a stable growing nucleus for the protofilament. Here we put together the elements of extensive knowledge about aggregation and nucleation kinetics, using a specific case of Aβ 1−42 amyloidogenic peptide for illustration, to find theoretical expressions for the effective rate of amyloid nucleation. We find that at low monomer concentration in solution, and also at low interaction energy between two peptide conformations in the micelle, the nucleation occurs via the classical route. At higher monomer concentration, and a range of other interaction parameters between peptides, the two-step 'aggregation-conversion' mechanism of nucleation takes over. In this regime, the effective rate of the process can be interpreted as a power of monomer concentration in a certain range of parameters, however, the exponent is determined by a complicated interplay of interaction parameters and is not related to the minimum size of the growing nucleus (which we find to be ∼ 7-8 for Aβ 1−42 ).

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Amyloid-β forms fibrils by nucleated conformational conversion of oligomers

Cited by 355 publications

References 51 publications

Proliferation of amyloid-β42 aggregates occurs through a secondary nucleation mechanism

Proliferation of amyloid-β42 aggregates occurs through a secondary nucleation mechanism

Unmasking the roles of N- and C-terminal flanking sequences from exon 1 of huntingtin as modulators of polyglutamine aggregation

Mechanisms and rates of nucleation of amyloid fibrils

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