The Solvent Protection of Alzheimer Amyloid-β-(1–42) Fibrils as Determined by Solution NMR Spectroscopy

Abstract

Alzheimer disease is a neurodegenerative disorder that is tightly linked to the self-assembly and amyloid formation of the 39 -43-residue-long amyloid-␤ (A␤) peptide. Considerable evidence suggests a correlation between Alzheimer disease development and the longer variants of the peptide, A␤-(1-42/43). Currently, a molecular understanding for this behavior is lacking. In the present study, we have investigated the hydrogen/deuterium exchange of A␤-(1-42) fibrils under physiological conditions, using solution NMR spectroscopy. Protein assemblies in the form of amyloid fibrils are today linked to a group of ϳ20 different syndromes, of which Alzheimer disease (AD), 2 as well as various forms of prion disorders, are among the most well known. Amyloids, in general, are composed of predominantly ␤-sheet structures, where the ␤-strands are arranged perpendicular to the fibrillar axis into a common so-called cross-␤ pattern (1-4). AD is a neurological disorder presenting itself as progressive dementia. The pathology is tightly linked to the aggregation of a 39 -43-residue-long peptide fragment denoted amyloid-␤ (A␤) derived as a result of proteolytic processing of the considerably larger amyloid precursor protein. Aggregated A␤ peptides are found in AD brains in the form of diffuse and senile plaques as well as in cerebrovascular tissues. Considerable experimental evidence suggests an important role of A␤-(1-42/43) in the progress of AD, because it represents the main constituent of the first deposits found in the course of disease development (5, 6) and if overproduced may result in early onset AD (7, 8) (for a recent review, see Ref.9). The mechanisms by which a cytotoxic effect is exerted in vivo and the reasons why a pathologic self-aggregation is induced in certain individuals are complex and at present not completely understood. Prevention of A␤ assembly therefore constitutes a considerable therapeutic challenge, where an increased understanding regarding the properties of amyloid, and the pathways leading to its formation, is of utmost importance.Because of the generic quaternary structure and the large size of amyloid structures, elucidation of their architecture provides a complicated problem, where traditional methods, such as crystal diffraction and solution NMR, are not readily applicable. However, two recent crystallographic studies on fibrous micro-crystals, grown from peptides with either seven or twelve residues, have revealed many interesting structural details about the cross-␤ spine of fibrils (10, 11). Solid-state NMR performed on dried fibrils provides an alternative to the above mentioned techniques and has been used extensively to investigate the structure of A␤ amyloid. Studies on A␤-(10 -35), A␤-(1-40), and A␤-(1-42) suggest an arrangement where fibrils are formed by extended parallel ␤-strands arranged into two sheets (12-14). The results suggest a fibrillar core involving residues Val 12 -Val 24 and Ala 30 -Ala 42 and a loop spanning between residues Val 24 -Ala 30 (15). The structural restrai...

Interprotofilament interactions between Alzheimer's Aβ 1–42 peptides in amyloid fibrils revealed by cryoEM

“…6). This orientation of A␤ is consistent with recent quenched H/D exchange NMR data showing that the C-terminal residues Lys-28-Ala-42 are well protected from solvent access compared with the N-terminal arm of the hairpin loop (14,25). Moreover, the C-terminal residues were more protected in A␤ 1-42 fibrils compared with A␤ 1-40 fibrils, consistent with differences in the suprastructure of the fibrils.…”

“…Recently, solid-state NMR (ss-NMR) spectroscopy has been used extensively to probe the atomic structures of A␤ and A␤ peptides in the fibrillar state (7)(8)(9)(10)(11), suggesting a hairpinlike arrangement of the peptides stacked within the fibril. More recently, the combination of quenched hydrogen/deuterium (H/D) exchange and solution NMR spectroscopy added yet another dimension to the ss-NMR models by identifying core regions of the fibril and revealing dynamic properties in solution (12)(13)(14)(15). However, these models have been limited to local intermolecular and intramolecular interactions and have therefore been unable to describe the supramolecular architecture of the fibril.…”

Molecular Engineering of a Secreted, Highly Homogeneous, and Neurotoxic Aβ Dimer

“…28 According to previous work, 17 residues 1À16 were added to the model in an extended conformation to account for the secondary structure of Aβ(1À42) in the fibrillar form. 29 Both termini were kept ionic as under physiological conditions. All dimer structures were electrically neutralized by the addition of an appropriate number of sodium counterions, solvated in a TIP3P 30 water box with a minimum distance of 15 Å to the border, and then subjected to a two-step restrained minimization.…”

Modular peptides from the thermoplastic squid sucker ring teeth form amyloid-like cross-β supramolecular networks

“…H/D exchange NMR studies denote strong protection factors for residues in A2 microfibers ( Figure 6B) comparable to amyloid peptides. [53,57] However, residues in A1 microfibers ( Figure 6D) exhibit even higher protection factors. These observations suggest that the presence of Pro allows the cross β-structure packing to relax by extending the hydrogen bond lengths, [84] possibly preventing premature aggregation and in turn ensuring further assembly of the supramolecular network, which could be consistent with the higher amount of β-sheet content predicted by MD simulations for the Pro-containing A2 peptide at equilibrium.…”

“…The exchange rates and protection factors of the fibers are comparable to those of robust Aβ (1-42) and Aβ (25-35) amyloid fibrils. [53,57] While the H/D exchange for all residues generally increased with temperature, we note an abnormal behaviour at 45ºC, where all residues not only exhibited a higher exchange than at 65ºC but also a large fluctuation in peak intensity, which is evidenced by the large error bars. It is important to note that such high standard deviations appear to be especially prominent at 45ºC and not at other temperatures, indicating that it represents an intrinsic feature of the peptide but is not due to experimental uncertainties.…”