Probing Structural Features of Alzheimer’s Amyloid-β Pores in Bilayers Using Site-Specific Amino Acid Substitutions

Department of Bioengineering, Department of Mechanical and Aerospace Engineering, and Material Science Program, University of California, San Diego, La Jolla, California 92093, United States.
Biochemistry (Impact Factor: 3.02). 01/2012; 51(3):776-85. DOI: 10.1021/bi2017427
Source: PubMed


A current hypothesis for the pathology of Alzheimer's disease (AD) proposes that amyloid-β (Aβ) peptides induce uncontrolled, neurotoxic ion flux across cellular membranes. The mechanism of ion flux is not fully understood because no experiment-based Aβ channel structures at atomic resolution are currently available (only a few polymorphic states have been predicted by computational models). Structural models and experimental evidence lend support to the view that the Aβ channel is an assembly of loosely associated mobile β-sheet subunits. Here, using planar lipid bilayers and molecular dynamics (MD) simulations, we show that amino acid substitutions can be used to infer which residues are essential for channel structure. We created two Aβ(1-42) peptides with point mutations: F19P and F20C. The substitution of Phe19 with Pro inhibited channel conductance. MD simulation suggests a collapsed pore of F19P channels at the lower bilayer leaflet. The kinks at the Pro residues in the pore-lining β-strands induce blockage of the solvated pore by the N-termini of the chains. The cysteine mutant is capable of forming channels, and the conductance behavior of F20C channels is similar to that of the wild type. Overall, the mutational analysis of the channel activity performed in this work tests the proposition that the channels consist of a β-sheet rich organization, with the charged/polar central strand containing the mutation sites lining the pore, and the C-terminal strands facing the hydrophobic lipid tails. A detailed understanding of channel formation and its structure should aid studies of drug design aiming to control unregulated Aβ-dependent ion fluxes.

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    • "The mechanism of AD-induced LTP suppression remains unknown. However, it has been postulated that cellular ionic dysregulation may contribute to AD pathology by embedding amyloid oligomers into the membrane to form amyloid channels [48] [56] [57], which in turn directly or indirectly alter membrane ion channel expression and activity [58-62]. Regular exercise is known to produce a positive effect on cognition and synaptic plasticity. "
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    • "Reconstituting Ab(1–42) with a planar lipid bilayer resulted in the formation of multimeric channel-like structures with symmetries suggesting tetramer or hexamer pore-like structures of Ab(Lin et al., 2001; Quist et al., 2005). The formation of a variety of similar aggregate structures in lipid membranes have also been demonstrated computationally (Capone et al., 2012; Tofoleanu and Buchete, 2012). Similar impacts on membranes due to exposure to Ab have been detected in cellular models. "
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