1. Distinct dimerization for various alloforms of the amyloid-beta protein: Aβ(1-40), Aβ(1-42), and Aβ(1-40)(D23N)
Sébastien Côté, Rozita Laghaei, Philippe Derreumaux, Normand Mousseau J Phys Chem B. 2012 Apr 5;116(13):4043-55. doi: 10.1021/jp2126366. Epub 2012 Mar 26.
The Amyloid-beta protein is related to Alzheimer's disease, and various experiments have shown that oligomers as small as the dimer are cytotoxic. Two alloforms are mainly produced: Aβ(1-40) and Aβ(1-42). They have very different oligomer distributions, and it was recently suggested, from experimental studies, that this variation may originate from structural differences in their dimer structures. Little structural information is available on the Aβ dimer, however, and to complement experimental observations, we simulated the folding of the wild-type Aβ(1-40) and Aβ(1-42) dimers as well as the mutated Aβ(1-40)(D23N) dimer using an accurate coarse-grained force field coupled to Hamiltonian-temperature replica exchange molecular dynamics. The D23N variant impedes the salt-bridge formation between D23 and K28 seen in the wild-type Aβ, leading to very different fibrillation properties and final amyloid fibrils. Our results show that the Aβ(1-42) dimer has a higher propensity than the Aβ(1-40) dimer to form β-strands at the central hydrophobic core (residues 17-21) and at the C-terminal (residues 30-42), which are two segments crucial to the oligomerization of Aβ. The free energy landscape of the Aβ(1-42) dimer is also broader and more complex than that of the Aβ(1-40) dimer. Interestingly, D23N also impacts the free energy landscape by increasing the population of configurations with higher β-strand propensities when compared against Aβ(40). In addition, while Aβ(1-40)(D23N) displays a higher β-strand propensity at the C-terminal, its solvent accessibility does not change with respect to the wild-type sequence. Overall, our results show the strong impact of the two amino acids Ile41-Ala42 and the salt-bridge D23-K28 on the folding of the Aβ dimer.
2. Correlative memory deficits, Abeta elevation, and amyloid plaques in transgenic mice
K Hsiao, P Chapman, S Nilsen, C Eckman, Y Harigaya, S Younkin, F Yang, G Cole Science. 1996 Oct 4;274(5284):99-102. doi: 10.1126/science.274.5284.99.
Transgenic mice overexpressing the 695-amino acid isoform of human Alzheimer beta-amyloid (Abeta) precursor protein containing a Lys670 --> Asn, Met671 --> Leu mutation had normal learning and memory in spatial reference and alternation tasks at 3 months of age but showed impairment by 9 to 10 months of age. A fivefold increase in Abeta(1-40) and a 14-fold increase in Abeta(1-42/43) accompanied the appearance of these behavioral deficits. Numerous Abeta plaques that stained with Congo red dye were present in cortical and limbic structures of mice with elevated amounts of Abeta. The correlative appearance of behavioral, biochemical, and pathological abnormalities reminiscent of Alzheimer's disease in these transgenic mice suggests new opportunities for exploring the pathophysiology and neurobiology of this disease.
3. Mixing Aβ(1-40) and Aβ(1-42) peptides generates unique amyloid fibrils
Linda Cerofolini, et al. Chem Commun (Camb). 2020 Aug 11;56(62):8830-8833. doi: 10.1039/d0cc02463e. Epub 2020 Jul 6.
Recent structural studies show distinct morphologies for the fibrils of Aβ(1-42) and Aβ(1-40), which are believed not to co-fibrillize. We describe here a novel, structurally-uniform 1 : 1 mixed fibrillar species, which differs from both pure fibrils. It forms preferentially even when Aβ(1-42) : Aβ(1-40) peptides are mixed in a non-stoichiometric ratio.
