159. ALZHEIMER'S DISEASE AND TOXIC AMYLOID CHANNELS: UNRAVELING THERAPEUTIC TARGETS BY ATOMIC FORCE MICROSCOPY, ELECTROPHYSIOLOGY, MD SIMULATION, AND PROTEIN ENGINEERING

Department: Mechanical & Aerospace Engineering
Research Institute Affiliation: Graduate Program in Materials Science and Engineering
Faculty Advisor(s): Ratneshwar Lal | Sungho Jin

Primary Student
Name: Laura S Connelly
Email: lconnell@ucsd.edu
Phone: 858-822-1321
Grad Year: 2013

Abstract
Alzheimer's disease (AD) is a misfolded protein disease characterized by the accumulation of β-amyloid (Aβ) peptide as senile plaques, progressive neurodegeneration, and memory loss. AD pathology is linked to the destabilization of cellular ionic homeostasis mediated by toxic pores made of Aβ peptides. Understanding the exact nature by which these pores conduct electrical and molecular signals could aid in identifying potential therapeutic targets for the prevention/treatment of AD. We examined the electrical activity of Aβ1-42 pores by conductance measurements in planar lipid bilayer (PLB) and 3D structure by atomic force microscope (AFM). We then compared the imaged structures with molecular dynamic simulation (MDS) models to predict its conformation as a function of amino acid sequence. Site-specific amino acid (AA) substitutions in the wildtype Aβ1-42 peptide yield information regarding the location and significance of individual AA residues to its characteristic structure-activity relationship. As a first step, we selected two AAs that our MD simulation predicted to inhibit or permit pore conductance. We report that Phe19 substitution with Pro eliminates conductance in PLB system. MD simulations predict a collapsed pore, which is supported by pore-like structures seen in AFM 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 amyloid-β from inducing ionic destabilization toxicity. The substitution of Phe20 with Cys shows similar conductance to the wildtype as well as structurally similar pore structures. MD simulations predict site 20 to face the nonpolar bilayer outside the pore and supports the previously predicted the beta-sheet structure. AFM studies show that F20C Aβ forms pore-like structures indistinguishable from the wildtype.

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