Globular Tetramers of β2-Microglobulin Assemble into Elaborate Amyloid Fibrils

Annamalai

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

et al. 2016

Amyloid fibrils are proteinaceous aggregates associated with diseases in humans and animals. The fibrils are defined by intermolecular interactions between the fibril-forming polypeptide chains, but it has so far remained difficult to reveal the assembly of the peptide subunits in a full-scale fibril. Using electron cryomicroscopy (cryo-EM), we present a reconstruction of a fibril formed from the pathogenic core of an amyloidogenic immunoglobulin (Ig) light chain. The fibril density shows a lattice-like assembly of face-to-face packed peptide dimers that corresponds to the structure of steric zippers in peptide crystals. Interpretation of the density map with a molecular model enabled us to identify the intermolecular interactions between the peptides and rationalize the hierarchical structure of the fibril based on simple chemical principles.

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Cryo-EM reveals the steric zipper structure of a light chain-derived amyloid fibril

Annamalai

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

et al. 2016

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

“…Previous studies have shown that these fibrils possess a parallel in register cross-β structure (29,30) assembled into multidomain filaments coiled together, described by cryo-EM (28). These fibrils bind amyloid-specific ligands such as serum amyloid P component with a similar affinity to their ex vivo counterparts (31).…”

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confidence: 92%

“…Here, we use β 2 m amyloid fibrils formed in vitro as a model system to investigate the structural basis of membrane damage by amyloid fibrils (27,28). Previous studies have shown that these fibrils possess a parallel in register cross-β structure (29,30) assembled into multidomain filaments coiled together, described by cryo-EM (28).…”

mentioning

confidence: 99%

Direct three-dimensional visualization of membrane disruption by amyloid fibrils

Milanesi

Sheynis

Xue

et al. 2012

Self Cite

169

177

Protein misfolding and aggregation cause serious degenerative conditions such as Alzheimer's, Parkinson, and prion diseases. Damage to membranes is thought to be one of the mechanisms underlying cellular toxicity of a range of amyloid assemblies. Previous studies have indicated that amyloid fibrils can cause membrane leakage and elicit cellular damage, and these effects are enhanced by fragmentation of the fibrils. Here we report direct 3D visualization of membrane damage by specific interactions of a lipid bilayer with amyloid-like fibrils formed in vitro from β 2 -microglobulin (β 2 m). Using cryoelectron tomography, we demonstrate that fragmented β 2 m amyloid fibrils interact strongly with liposomes and cause distortions to the membranes. The normally spherical liposomes form pointed teardrop-like shapes with the fibril ends seen in proximity to the pointed regions on the membranes. Moreover, the tomograms indicated that the fibrils extract lipid from the membranes at these points of distortion by removal or blebbing of the outer membrane leaflet. Tiny (15-25 nm) vesicles, presumably formed from the extracted lipids, were observed to be decorating the fibrils. The findings highlight a potential role of fibrils, and particularly fibril ends, in amyloid pathology, and report a previously undescribed class of lipid-protein interactions in membrane remodelling.T he failure of molecular chaperones to prevent the accumulation of misfolded proteins results in protein aggregation and amyloid formation, processes associated with severe human degenerative diseases (1, 2). Despite the attention focused on these problems during the century since these disorders were first identified (3-5) and advances in understanding the structure of the cross-β conformation of amyloid fibrils in atomic detail (6, 7), the basic pathological mechanisms of amyloidosis remain poorly understood and therapeutic intervention is lacking. The identity of the toxic species and the mechanisms of cytotoxicity remain major unsolved problems. In some systems, there is evidence suggesting that prefibrillar oligomers, rather than the fully formed fibrils, are the source of toxicity (8, 9). In these cases, cytotoxicity is thought to result from the formation of specific membrane pores (10, 11) although alternative models including membrane destabilization or membrane thinning have also been proposed (12-15). In other cases, toxicity may reside with the amyloid fibrils themselves. Evidence that toxicity correlates with fibrillar assemblies has been reported for yeast and mammalian prion proteins (16, 17), human lysozyme (18), Huntingtin exon 1, α-synuclein (19), and Amyloid-β (Aβ) (20, 21). Furthermore, Aβ plaques have been shown to form rapidly in vivo and to precede neuropathological changes in a mouse model (22). The end surfaces of fibrils (herein termed "fibril ends") are unusually reactive entities: they play a key role in catalyzing recruitment and conformational conversion of amyloid-forming proteins (23, 24) and provide the sites for templated...

J. Am. Soc. Mass Spectrom.

“…Low-resolution details of intact amyloid fibrils, which can be generated by electron microscopy (EM) [17], cryo-EM [18], and atomic force microscopy (AFM) [19,20], have shown that fully assembled amyloid fibrils may contain different numbers of protofilaments, either intertwined into helices or bound side-to-side in a twisted ribbon structure [21,22], in which the ␤-strands are arranged perpendicular to the fibril axis.…”

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confidence: 99%

Mass spectrometry and the amyloid problem—How far can we go in the gas phase?

Ashcroft

2010

A number of proteins are capable of converting from their soluble, monomeric form into highlyordered, insoluble aggregates known as amyloid fibrils. In vivo, these fibrils, which accumulate in organs and tissues, are associated with a wide range of amyloid diseases for which there are currently no therapeutic solutions. The molecular details of the pathway from native monomer through oligomeric intermediates to the final amyloid fibril remain a challenging enigma. Over the past few years, mass spectrometry has been applied to investigate the various stages of amyloid fibril formation, and this report summarizes the key steps achieved to date. (J Am Soc Mass Spectrom 2010, 21, 1087-1096