Toxic fibrillar oligomers of amyloid-β have cross-β structure

Abstract

Although amyloid fibers are found in neurodegenerative diseases, evidence points to soluble oligomers of amyloid-forming proteins as the cytotoxic species. Here, we establish that our preparation of toxic amyloid-β 1-42 (Abeta42) fibrillar oligomers (TABFOs) shares with mature amyloid fibrils the cross-β structure, in which adjacent β-sheets adhere by interpenetration of protein side chains. We study the structure and properties of TABFOs by powder X-ray diffraction, EM, circular dichroism, FTIR spectroscopy, chromatography, conformational antibodies, and celluar toxicity. In TABFOs, Abeta42 molecules stack into short protofilaments consisting of pairs of helical β-sheets that wrap around each other to form a superhelix. Wrapping results in a hole along the superhelix axis, providing insight into how Abeta may form pathogenic amyloid pores. Our model is consistent with numerous properties of Abeta42 fibrillar oligomers, including heterogenous size, ability to seed new populations of fibrillar oligomers, and fiber-like morphology.Abeta oligomers | toxic oligomers | Alzheimer's disease | domain swapping | protein aggregation S everal neurodegenerative diseases are correlated with amyloid fibrillar deposits (1). For a number of these diseases, it has been postulated that amyloid fibers may not play the primary causative role (2). Rather, soluble aggregates of the amyloidogenic proteins are likely the relevant etiological agents (2, 3). The most prevalent of these neurodegenerative diseases, Alzheimer's disease (4), is strongly linked to the presence of soluble aggregates of amyloid-β (Abeta) (5). Abeta aggregates have been shown to impair neurite function (6), synaptic morphology (7), cognitive function (8), and cell viability (9). In the prion conditions, also classed as amyloid diseases (10), small oligomers have also been identified as the toxic species (11). Recently, the availability of structure-specific antibodies has provided a means to group oligomers into two broad antigenic categories known as prefibrillar and fibrillar oligomers (12). Fibrillar oligomers are recognized by the OC antibody isolated from rabbits immunized with Abeta fibers (13), suggesting that Abeta fibrillar oligomers share surface features with Abeta fibers. In addition to fiber-like morphology, fibrillar oligomers are similar to fibers in that fibrillar oligomers can seed new populations of fibrillar oligomers (14). The ability to seed suggests that, like fibers, fibrillar oligomers are organized into a repeating array or lattice of monomers, wherein the monomers have identical structures. Fibrillar oligomers likely have a distinct lattice from fibers, because Abeta fibrillar oligomers do not seed Abeta fiber formation (14). Here, we characterize a particular preparation of fibrillar oligomers that we term toxic Abeta 1-42 (Abeta42) fibrillar oligomers (TABFOs).The structure of amyloid fibers may provide insight into the structure of fibrillar oligomers. Fiber diffraction studies of chemically pure amyloid display a cross-β diffraction...

On the lack of polymorphism in Aβ‐peptide aggregates derived from patient brains

“…17 The possibility that oligomers of Ab could be formed outside the membrane, bind to the cell surface and then span the membrane for the formation of active channels has been proposed by Shafrir et al 31 Further computational studies of Ab aggregation with three-fold symmetry in the presence of lipid membranes may help to identify which of the amyloid peptide models are stable and remain sufficiently open for ion diffusion. Note that a similar pore with side chains of M 35 lining the inner surface was also observed by Stroud et al 15 in the toxic Ab42 fibrillar oligomer model.…”

Pulsed hydrogen–deuterium exchange mass spectrometry probes conformational changes in amyloid beta (Aβ) peptide aggregation

“…By using this method, we successfully decoupled the aggregation from the HDX process. Importantly, we extracted kinetic information on the Aβ 42 aggregation at 25°C, indicating that the middle region of the Aβ 42 peptide (i.e., [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] was the "seeding" region in aggregation, followed by the C-terminus hydrophobic region (i.e., [36][37][38][39][40][41][42] and then the N-terminus hydrophilic region (i.e., [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Finally, we showed that this approach allowed us to examine directly the factors that affect the oligomerization of Aβ 42 .…”

“…Studies of amyloid fibrils invoke X-ray crystallography (22)(23)(24), EM (19,25,26), and thioflavin T fluorescence (19,27), revealing the polypeptide's global behavior, whereas NMR studies provide residue-level information for the fibrils (28)(29)(30). Nevertheless, we know little about soluble Aβ aggregates owing to their intrinsically high heterogeneity.…”

Mechanisms and rates of nucleation of amyloid fibrils

“…84 . In this scenario, it is clear that the collision between monomers and the critical nuclei is the non-spherical case, and in fact, no theoretical formula of the collision rate is available for such a complicated shape.…”