Simultaneous analysis of oligomer and fibril assembly kinetics reveals inhibitory effects of metastable oligomers on amyloid fibril formation.
The mechanisms linking deposits of insoluble amyloid fibrils to the debilitating neuronal cell death characteristic of neurodegenerative diseases remain enigmatic. Recent findings implicate transiently formed intermediates of mature amyloid fibrils as the principal toxic agent. Hence, determining which intermediate aggregates represent on-pathway precursors or off-pathway side branches is critical for understanding amyloid self-assembly, and for devising therapeutic approaches targeting relevant toxic species. We examined amyloid fibril self-assembly in acidic solutions, using the model protein hen egg-white lysozyme. Combining in situ dynamic light scattering with calibrated atomic-force microscopy, we monitored the nucleation and growth kinetics of multiple transient aggregate species, and characterized both their morphologies and physical dimensions. Upon incubation at elevated temperatures, uniformly sized oligomers formed at a constant rate. After a lag period of several hours, protofibrils spontaneously nucleated. The nucleation kinetics of protofibrils and the tight match of their widths and heights with those of oligomers imply that protofibrils both nucleated and grew via oligomer fusion. After reaching several hundred nanometers in length, protofibrils assembled into mature fibrils. Overall, the amyloid fibril assembly of lysozyme followed a strict hierarchical aggregation pathway, with amyloid monomers, oligomers, and protofibrils forming on-pathway intermediates for assembly into successively more complex structures.
Micrometer-scale poly(N-isopropylacrylamide) (poly-NIPAAm) hydrogel monolith patterns were fabricated on solid surfaces using soft lithography. At sufficiently high aspect ratios, the hydrogel monoliths swell and contract laterally with temperature. The spaces between the monoliths form a series of trenches that catch, hold, and release appropriately sized targets. A series of poly-NIPAAm monoliths were fabricated with dry dimensions of 40 microm height, 12 microm diameter, and a spacing of 12 microm between monoliths. Above the lower critical solution temperature (LCST), the monoliths collapse to their dry dimensions and the spacing between monoliths is 12 microm. Below the LCST, the monoliths swell by 70% in the lateral direction, reducing the gap size between monoliths to 3 microm. The potential use of the hydrogel monoliths as size-selective "catch and release" structures was demonstrated with a mixture of 6 and 20 microm polystyrene microspheres, where the 6 microm diameter particles were selectively concentrated and separated from the larger particles.
Amyloid-b peptides (Ab) assemble into both rigid amyloid fibrils and metastable oligomers termed AbO or protofibrils. In Alzheimers disease, Ab fibrils constitute the core of senile plaques, but Ab protofibrils may represent the main toxic species. Ab protofibrils accumulate at the exterior of senile plaques, yet the protofibril-fibril interplay is not well understood. Applying chemical kinetics and atomic force microscopy to the assembly of Ab and lysozyme, protofibrils are observed to bind to the lateral surfaces of amyloid fibrils. When utilizing Ab variants with different critical oligomer concentrations, the interaction inhibits the autocatalytic proliferation of amyloid fibrils by secondary nucleation on the fibril surface. Thus, metastable oligomers antagonize their replacement by amyloid fibrils both by competing for monomers and blocking secondary nucleation sites. The protofibril-fibril interaction governs their temporal evolution and potential to exert specific toxic activities.
Zinc oxide (ZnO) nanostructures have attracted great attention as a promising functional material with unique properties suitable for applications in UV lasers, light emitting diodes, field emission devices, sensors, field effect transistors, and solar cells. In the present work, ZnO nanowires have been synthesized on an n-type Si substrate using a hydrothermal method where surfactant acted as a modifying and protecting agent. The surface morphology, electrochemical properties, and opto-electrochemical properties of ZnO nanowires are investigated by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), cyclic voltammetry, and impedance spectroscopy techniques. The cycling characteristics and rate capability of the ZnO nanowires are explored through electrochemical studies performed under varying electrolytes. The photo response is observed using UV radiation. It is demonstrated that crystallinity, particle size, and morphology all play significant roles in the electrochemical performance of the ZnO electrodes.
A hydrothermal synthesis of densely packed ZnO nanowires was realized in a confined space via forced circulation of the heated growth solution through microfluidic channels formed primarily by a set of high aspect ratio trenches in a Si substrate. A uniform and conformal seeding layer of ZnO was deposited to cover the entire surface of the trenches by means of atomic layer deposition (ALD). Densely packed ZnO nanowires were formed inside the trenches with particularly good coverage over the sidewalls, where they would not grow effectively through a conventional hydrothermal method. The strategy for controlled growth of densely packed ZnO nanowires over such high aspect ratio microstructures is deemed beneficial when these microstructures are employed as electrodes with high specific surface areas for devices such as supercapacitors or any other electrochemical devices.
Amyloid‐β peptides (Aβ) assemble into both rigid amyloid fibrils and metastable oligomers termed AβO or protofibrils. In Alzheimer's disease, Aβ fibrils constitute the core of senile plaques, but Aβ protofibrils may represent the main toxic species. Aβ protofibrils accumulate at the exterior of senile plaques, yet the protofibril–fibril interplay is not well understood. Applying chemical kinetics and atomic force microscopy to the assembly of Aβ and lysozyme, protofibrils are observed to bind to the lateral surfaces of amyloid fibrils. When utilizing Aβ variants with different critical oligomer concentrations, the interaction inhibits the autocatalytic proliferation of amyloid fibrils by secondary nucleation on the fibril surface. Thus, metastable oligomers antagonize their replacement by amyloid fibrils both by competing for monomers and blocking secondary nucleation sites. The protofibril—fibril interaction governs their temporal evolution and potential to exert specific toxic activities.
We report the robust attachment of glycosaminoglycans (GAGs) on silanized glass surfaces. Depositions were performed both by immersion and by application of a pattern by means of microcontact printing. Immunofluorescence assays were performed to verify the deposition and the quality of the patterns. In addition, AFM studies of the coated surfaces were performed in order to study some physical characteristics of the deposited GAGs layers. These results may prove useful for the characterization of the mechanical properties of GAGs in the glycocalyx and its relation with cellular migration.
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