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

Abstract

A lzheimer's disease (AD) is the most prevalent neurodegenerative disorder with the amyloid-β-peptide (Aβ) playing a central role in its pathogenesis. 1 Aβ is generated as a 38À43 residue peptide from the amyloid precursor protein (APP) by the proteolytic activity of β-and γ-secretases. 2,3 Aβ assembles into oligomers of various sizes and Aβ plaques, a neuropathological hallmark of AD. 1 Unlike Aβ fibrils or plaques, only the presence of Aβ oligomers correlates with the cognitive status of AD. 4,5 Aβ oligomers cause synaptic pathology 1,6 in line with findings that loss of dendritic spines correlates to early morphological changes in AD patients. 7 Many different oligomeric Aβ species have been identified, 8À10 and neurotoxicity has been attributed to Aβ dimers, 6 Aβ dodecamers, 10,11 or others. A recent study from Shankar et al. 6 has provided solid evidence that natively secreted Aβ dimers purified from post-mortem brains of patients with clinical AD are the predominant species sufficient to cause synaptic pathology. To gain insight into structureÀfunction relationships of Aβ dimers, it is of paramount importance to generate or purify highly homogeneous, distinct species of Aβ oligomers. So far, detailed structural investigations of native Aβ oligomers have been hampered by their low abundance in available transgenic mouse models of AD or AD patient brains, and laborious purification procedures.Synthetic Aβ has been a convenient tool for studying Aβ protein biochemistry, since it can be generated to relatively high purity in large amounts and is therefore readily available for biophysical and structural studies of some aspects of Aβ. However, evidence has accumulated suggesting that synthetic Aβ oligomers are only insufficiently modeling naturally secreted Aβ oligomer functions, even if refolded and purified by laborious procedures. Several studies clearly indicate that the bioactivity of naturally secreted Aβ oligomers from transfected cells is similar to that of AD brain-derived Aβ oligomers, but more than hundred times stronger than that of synthetic Aβ oligomers, when long-term potentiation (LTP) effects are taken as readout. 12 The major difference between natively secreted and synthetic Aβ is that natively secreted Aβ is the result of a highly controlled and quality-checked, cofactor-assisted proteolytic process at low local concentrations, while bulk refolding of synthetic Aβ occurs without regulating cofactors at high local concentrations. Bulk refolding leads to conformational heterogenetiy of refolded Aβ oligomers correlating with different neurotoxicities. 13 Received: February 20, 2011 Accepted: March 11, 2011 ABSTRACT: Aβ oligomers play a key role in the pathophysiology of Alzheimer's disease. Research into structureÀfunction relationships of Aβ oligomers has been hampered by the lack of large amounts of homogeneous and stable material. Using computational chemistry, we designed conservative cysteine substitutions in Aβ aiming at accelerating and stabilizing assembly of Aβ dimers by an intermolecu...

Role of the N-terminus for the stability of an amyloid-β fibril with three-fold symmetry

“…the English (His6Arg) and the Tottori (Asp7His) mutant, which show accelerated fibril formation [13, 14]. Phosphorylation of Ser8 significantly changes the fibril topology [15], whereas a Ser8Cys mutation favors the formation of soluble dimers by oxidative crosslinking [16, 17]. Metal ions like Zn 2+ bind to N-terminal residues and accelerate amyloid formation [18–20].…”

An Account of Amyloid Oligomers: Facts and Figures Obtained from Experiments and Simulations

“…Dimers can be detected ex vivo in cerebrospinal fluid (CSF) as well as in neural cells . Experimental models of the Aβ dimer mostly rely on two monomers covalently linked by a disulfide bridge—Aβ(1–40)Cys26 dimers, AβSer8Cys, AβMet35Cys, or Aβ(1–40)Cys2, for example—or a dimer linked by a C‐terminal (Gly) 3 Cys addition . Systematic proline substitution at positions 15–32 served to identify β‐strand and β‐turn regions that are essential both for aggregation and for neurotoxicity.…”

Coarse‐grained and All‐atom Simulations towards the Early and Late Steps of Amyloid Fibril Formation

“…Aβ 1–42 WT sequence, DAEFRHDSGYEVHHQKLVFFAEDVGSNKGAIIGLMVGGVVIA, has two hydrophobic patches, L17‐A21 (CHC) and A30‐A42 (C‐terminus), and two hydrophilic patches, E22‐G29 (loop region) and D1‐K16 (N‐terminus) . The challenge also comes from the lack of high‐resolution structures and formation/dissociation rates of the low molecular weight Aβ 1–40/1–42 oligomers, including dimers, which are believed to be the most critical players in the pathology;, and for these oligomers, we have at hand low‐resolution structural data . Finally, the experimental sigmoidal kinetics of amyloid formation is the result of a linear combination of microscopic reactions involving primary classical and secondary (fragmentation and surface‐dependent lateral) nucleation processes, and we know little on the topology and size of the primary nucleus .…”