Effects of Point Substitutions on the Structure of Toxic Alzheimer's beta-Amyloid Channels: Atomic Force Microscopy and Molecular Dynamics Simulations

Alzheimer's disease (AD) is a misfolded protein disease characterized by the accumulation of beta-amyloid (A beta) peptide as senile plaques, progressive neurodegeneration, and memory loss. Recent evidence suggests that AD pathology is linked to the destabilization of cellular ionic homeostasis mediated by toxic pores made of A beta peptides. Understanding the exact nature by which these pores conduct electrical and molecular signals could aid in identifying potential therapeutic targets for the prevention and treatment of AD. Here using atomic force microscopy (AFM) and molecular dynamics (MD) simulations, we compared the imaged pore structures with models to predict channel conformations as a function of amino acid sequence. Site-specific amino acid (AA) substitutions in the wild-type A beta(1-42) peptide yield information regarding the location and significance of individual AA residues to its characteristic structure activity relationship. We selected two AAs that our MD simulation predicted to inhibit or permit pore conductance. The substitution of Phe19 with Pro has previously been shown to eliminate conductance in the planar lipid bilayer system. Our MD simulations predict a channel-like shape with a collapsed pore, which is supported by the AFM channel images. We suggest that proline, a known beta-sheet breaker, creates a kink in the center of the pore and prevents conductance via blockage. This residue may be a viable target for drug development studies aiming to inhibit A beta from inducing ionic destabilization toxicity. The substitution of Phe20 with Cys exhibits pore structures indistinguishable from the wild type in AFM images. MD simulations predict site 20 to face the solvated pore. Overall, the mutations support the previously predicted beta-sheet-based channel structure.

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