Antiparallel β-Sheet Structure within the C-Terminal Region of 42-Residue Alzheimer's Amyloid-β Peptides When They Form 150-kDa Oligomers

Abstract

Understanding the molecular structures of amyloid-β (Aβ) oligomers and underlying assembly pathways will advance our understanding of Alzheimer’s disease (AD) at the molecular level. This understanding could contribute to disease prevention, diagnosis, and treatment strategies, as oligomers play a central role in AD pathology. We have recently presented a procedure for production of 150 kDa oligomeric samples of Aβ(1–42) (the 42-residue variant of the Aβ peptide) that are compatible with solid state NMR analysis, and we have shown that these oligomers and amyloid fibrils differ in intermolecular arrangement of β-strands. Here we report new solid state NMR constraints that indicate antiparallel intermolecular alignment of β-strands within the oligomers. Specifically, 150 kDa Aβ(1–42) oligomers with uniform 13C and 15N isotopic labels at I32, M35, G37 and V40 exhibit β-strand secondary chemical shifts in 2D fpRFDR NMR spectra, spatial proximities between I32 and V40 as well as between M35 and G37 in 2D DARR spectra, and close proximity between M35 Hα and G37 Hα in 2D CHHC spectra. Furthermore, 2D DARR analysis of an oligomer sample prepared with 30% labeled peptide indicates that the I32-V40 and M35-G37 contacts are between residues on different molecules. We employ molecular modeling to compare the newly derived experimental constraints with previously proposed geometries for arrangement of Aβ molecules into oligomers.

Structural, morphological, and functional diversity of amyloid oligomers

“…Subsequent NMR analysis determined that in this oligomer population, C-terminal b-sheet (residues 22-39) was included into the secondary structure formation, whereas the N-terminal half of the peptide was unstructured due to the EGCG binding [32]. In Ab 42 oligomers formed in the presence of SDS, residues 25-40 were found to form b-strands that were arranged in the antiparallel fashion, whereas the structure of the N-terminal half of the peptide was unclear [14,18]. An EPR investigation of oligomers prepared under the similar conditions indicated gradual increase in the structural order towards the C-terminus of the peptide and antiparallel arrangement of b-strands [18].…”

Molecular Structure of Aggregated Amyloid-β: Insights from Solid-State Nuclear Magnetic Resonance

“…A variety of oligomeric and protofibrillar states have been partially characterized by ssNMR (Ahmed et al 2010; Scheidt et al 2011; Lopez del Amo et al 2012; Scheidt et al 2012; Tay et al 2013; Lendel et al 2014; Sarkar et al 2014; Huang et al 2015; Parthasarathy et al 2015; Potapov et al 2015). The main finding, originally reported by Ishii and coworkers (Chimon and Ishii 2005; Chimon et al 2007), is that the Aβ conformation in nonfibrillar intermediates is remarkably similar to the conformation in fibrils.…”

“…A detailed model a metastable Aβ protofibril has also been developed from ssNMR data (Qiang et al 2012). Complete models for oligomeric Aβ assemblies have not yet been developed, but a substantial body of experimental data has been obtained for samples with a variety of morphologies, prepared under a variety of in vitro conditions (Chimon and Ishii 2005; Chimon et al 2007; Ahmed et al 2010; Scheidt et al 2011; Lopez del Amo et al 2012; Scheidt et al 2012; Tay et al 2013; Lendel et al 2014; Sarkar et al 2014; Huang et al 2015; Parthasarathy et al 2015; Potapov et al 2015). …”

Role of dietary antioxidant (−)-epicatechin in the development of β-lactoglobulin fibrils

“…Irrespective of the native protein structure, amyloid fibrils show common features with protein β-strands arranged perpendicular to the elongation axis. However, recent studies suggested that their toxicity may be related to certain differences in the fibril structural and biochemical properties [2,3]. Unfortunately, a precise relation between fibril polymorphism, resulting from aggregation of monomers and oligomers with different conformational properties, and toxicity is difficult to assess [4].…”