Force Spectroscopy Setup.

<p>A schematic of experimental setup of force spectroscopy experiment showing Aβ bound to substrate and tip via the PEG linker.</p

Proposed structures of Aβ dimers with and without copper assembled from stable Aβ(1–42) monomer structures.

<p>Each monomer has an internal antiparallel β-sheet between residues 18–21 and 30–33. The dimers are assembled by juxtaposition of the self-recognition site residues 18–21 in antiparallel (A, C) and parallel (B, D) orientation. Both orientations bring His6, His13 and His14 of each monomer into close proximity, requiring little reorientation to bind Cu²⁺ ions (filled green circles). Structures are courtesy of D. F. Raffa and A. Rauk, Molecular Dynamics Study of the Beta Amyloid Peptide of Alzheimer's Disease and its Divalent Copper Complexes <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0059005#pone.0059005-Raffa1" target="_blank">[53]</a>, created using Raswin software.</p

Effect of Copper on Aβ rupture force.

<p>Histograms show the distribution of forces required to rupture the Aβ-Aβ complex without copper (A) and with copper (B). Fits to the data are Gaussian distributions, the peaks of which represent the most probable rupture force.</p

Schematic diagram of Aβ dimers with and without copper.

<p>Without copper, the most favorable conformation of the Aβ dimer involves an anti-parallel conformation (A). With the addition of copper, Aβ adopts a parallel dimer conformation (B) stabilized by the occupied copper binding sites (C).</p

Statistical Data of Force Spectroscopy Experiments.

<p>Statistical Data of Force Spectroscopy Experiments.</p

AFM images of amyloid-metal aggregates.

<p>AFM images of Aβ incubated without copper for periods of 1 hr (A) 6 hr (B) and 24 hr (C), and with copper at a 10∶1 molar ratio for 1 hr (D), 6 hr (E), and 24 hr (F). The lateral scale bar is 1 µm.</p

Representative force curves.

<p>Force curves showing rupture forces of an Aβ dimer without (A) and with (B) copper added at a retraction rate of 400 nm/s. Curves are shown as force vs. piezo z-displacement.</p

Schematic of Aβ interacting with a model membrane (not to scale).

<p>Arrangement of lipids present model bilayer system and phase separation leads to membrane nonhomogeneity, i.e., the presence of nanodomains, both topographical (Δh) and electrostatic (ΔV).</p

Force vs loading rate plots for Aβ42 dimer dissociation in aqueous, Cu²⁺ [20nM], and Zn²⁺ [20nM] environments.

<p>The force plots have been fit with the Friddle-De Yoreo reversible binding model [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0147488#pone.0147488.ref034" target="_blank">34</a>]. Adjusted R² values of fits are 0.979, 0.897, and 0.808 for aqueous, copper, and zinc data, respectively.</p

Mechanically induced Aβ binding and dissociation.

<p>(A) is a representative experimental force plot: the tip approaches the sample (red line) and when it touches the surface—the cantilever bends (steep linear region). The two surface-bound monomers are allowed to bind (red to blue transition at top of linear region. The cantilever retracts (blue steep linear region). As the cantilever returns to its neutral position, the force plot passes through the base line. At this point the system is in its minimum free energy state (B). The cantilever is not deflected and the system resembles a stable dimeric state (B). As the cantilever retracts, a mechanical force is applied along the reaction coordinate and the free energy of the system increases (E). The system reaches its maximum free energy just prior to rupture at x = x_β (E) at which point the cantilever is at its maximum deflection (C). At dissociation, the cantilever returns to its neutral position (D) and all free energy of the system is lost [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0147488#pone.0147488.ref040" target="_blank">40</a>].</p