Visualizing Super-Diffusion, Oligomerization, and Fibrillation of Amyloid-β Peptide Chains along Tubular Membranes

HSAFM-MIREBA - Methodology for Inferring REsolution in biological applications

Due to a lack of requirement for any direct labelling of the target molecule, high speed atomic force microscopy (HS-AFM) is a potentially powerful procedure for the assessment of biological processes involving macromolecules. When the sample is static the AFM device can be purposefully setup to recover high-resolution information about the feature in question. However, when the feature to be studied moves an appreciable amount during the course of the measurement, the obtained image will be blurred. Encountering such blurred observations prompts the experimenter to sacrifice higher resolution images for higher scanning speeds by tuning available experimental parameters (such as the scanned image area, the image pixel size, the resonance frequency of the cantilever and/or the diameter of the AFM tip). The present work describes a software tool, HSAFM-MIREBA (High Speed Atomic Force Microscopy - Methodology for Inferring REsolution in Biological Applications) that allows for pre-experimental optimization of such parameters through iterative rounds of simulation of both the dynamic surface process and the HS-AFM measurement (based on the particular set of governing parameters). A representative set of five dynamic biological processes that describe a range of diffusive and directed motions (which can themselves be tuned by altering characteristic governing parameter sets) are provided.

Physical Mechanism of Amyloid-β Peptide Chain Aggregation on Fluidic Lipid Nanotubules

The question of how peptide chain aggregation is influenced by lipid membranes with varying shapes and structures is crucial for a detailed understanding of the neurotoxicity effect of the peptide chains. Not like the more usual spherical liposomes and planar lipid membranes, herein, we use lipid nanotubules as a model of important neuron synapse nanowire structures and devote particular attention to the effect of nanotubule fluidity on amyloid-β peptide (Aβ) chain aggregation. We apply single-molecule tracking (SMT) to elucidate how Aβ chains diffuse and aggregate on lipid nanotubules with different fluidities. The physical mechanism implies that fluidic lipid nanotubules facilitate the super-diffusion of two-dimensional (2D)-mobile precursor Aβ chains and promote their aggregation. This aggregation mechanism is retarded on less fluidic lipid nanotubules where the super-diffusion of 2D-mobile precursor Aβ chains is restricted by "frozen" lipids with less mobility. This work provides a mechanistic explanation for Aβ chain aggregation on fluidic lipid nanotubules.

Effect of Surface-Chelated Cu2+ on Amyloid-β Peptide Fibrillation

Abnormal interactions of copper (Cu) ions with amyloid-β (Aβ) peptides are believed to play an important role in the pathogenesis of Alzheimer's disease (AD). However, there is still debate as to the exact role of Cu ions in Aβ amyloidosis despite extensive studies on Aβ-Cu interactions. Unlike previously reported works, we herein study the effect of surface-chelated Cu²⁺, rather than the more usual solution-phase dissolved Cu²⁺, on Aβ aggregation. Through the combination of single molecule fluorescent tracking, atomic force microscopy imaging experiments, and all-atom molecular dynamic simulations, we show that the surface-chelated Cu²⁺ dynamically interacts with Aβ chains, restricts their 2D-diffusivity on the surface, and retards their fibrillation, while the designated surfaces without Cu²⁺ facilitate the 2D-diffusivity of Aβ chains for better interpeptide interaction and promote Aβ fibrillation. We offer a microscopic molecular insight into the retardation mechanism of surface-chelated Cu²⁺ on Aβ fibrillation, suggesting that the surface-bound pools of metal ions are critical in AD progression and drug design.