Amyloid-β protein oligomerization and the importance of tetramers and dodecamers in the aetiology of Alzheimer's disease

Abstract

In recent years, small protein oligomers have been implicated in the aetiology of a number of important amyloid diseases, such as type 2 diabetes, Parkinson's disease and Alzheimer's disease. As a consequence, research efforts are being directed away from traditional targets, such as amyloid plaques, and towards characterization of early oligomer states. Here we present a new analysis method, ion mobility coupled with mass spectrometry, for this challenging problem, which allows determination of in vitro oligomer distributions and the qualitative structure of each of the aggregates. We applied these methods to a number of the amyloid-β protein isoforms of Aβ40 and Aβ42 and showed that their oligomer-size distributions are very different. Our results are consistent with previous observations that Aβ40 and Aβ42 self-assemble via different pathways and provide a candidate in the Aβ42 dodecamer for the primary toxic species in Alzheimer's disease.Many diseases share the common trait of peptide-protein misfolding that leads to oligomerization and, eventually, formation of plaques of β-sheet structure. Prominent among these are type 2 diabetes 1 , Parkinson's disease 2 and Alzheimer's disease 3,4 . Of these, Alzheimer's disease is the leading cause of late-life dementia and is the focus of this paper. An increasing body of evidence links oligomerization of a ubiquitous peptide, the amyloid-β [3][4][5][6] . For this reason, elucidation of pathways of oligomer formation may be critical for the identification of therapeutic targets.Many types of oligomeric amyloid-β assemblies have been described (for a review, see Lazo et al. 7 ). Recently, Bitan et al. [8][9][10] used photoinduced cross-linking of unmodified proteins (PICUP) to reveal that the 42-residue form of amyloid-β, Aβ42, formed (Aβ42) 5 and (Aβ42) 6 oligomers ('paranuclei') that could oligomerize to form structures of higher order. Aβ40 did not form paranuclei, but instead existed as a mixture of monomers, dimers, trimers and tetramers. Chen and Glabe 11 , in contrast, used fluorescence and gel electrophoresis to determine oligomer states of amyloid-β refolded from denaturing solutions. They observed only Aβ42 monomer and trimer bands, and no oligomers of Aβ40. Differences such as these may exist because of the diverse experimental systems used to monitor amyloid-β selfassociation. Also, it has been argued that, in addition to the intrinsic potential of amyloid-β to traverse different assembly pathways, flaws in experimental design may have misled researchers in their quest to elucidate fully the amyloid-β oligomerization process 12 . Hence there is significant uncertainty about amyloid-β oligomer states and their position and relevance to amyloid-β aggregation. Results and discussionWe used a different, more direct, method to probe the amyloid-β oligomerization process: ion mobility coupled with mass spectrometry [13][14][15] . Details are given in the Methods section.Here the results for Aβ40 are given as an example. The mass spectrum of Aβ40 is s...

Distinct higher-order α-synuclein oligomers induce intracellular aggregation

“…Similar oligomeric conformations have been documented in the case of Aβ 42 (where Aβ is amyloid β-peptide) oligomers, with dimers, tetramers, hexamers and dodecamers being observed and correlated with toxicity, but no odd number oligomers were detected. The higher-order oligomers obtained a ring-like structure very similar to that observed in our study [40,53] and ring assemblies have been observed by other methods such as AFM [54]. The structural collapse and assembly of α-syn seen on aggregation also has precedents.…”

“…A 4 or 8 Å overlap between different subunits was allowed, giving a centre-to-centre distance of 36 or 32 Å which is comparable to the most compact forms of the dimer measured here. This modelling approach is similar to that used for the oligomers involved in Alzheimer's disease [40]. A range of conformations including linear structures, closed ring and open ring forms have been constructed to model the experimentally acquired with centre-to-centre distance of 36 or 32 Å.…”

Synaptic Amyloid-β Oligomers Precede p-Tau and Differentiate High Pathology Control Cases

“…This result is consistent with previous work showing that the Ab42 tetramer structure is likely to be stable and long-lived and serves as a module for formation of larger Ab assemblies. 49 A prominent set of bands at approximately 55 kDa seems likely to include Ab*56. 50 …”

Gas-Phase Hydrogen-Deuterium Exchange Labeling of Select Peptide Ion Conformer Types: a Per-Residue Kinetics Analysis

“…Biomolecular ion structure analysis utilizing IMS has an extensive history [19,20,[30][31][32]. The development of IMS instrumentation [20,[33][34][35][36][37][38][39][40], theory [41][42][43][44][45], and applications [46][47][48][49][50] is described in the literature.…”