Search

Prions are lipidated proteins that interact with endogenous lipids and metal ions. They also assemble into multimers and propagate into the infectious scrapie form known as PrP(Sc). The high-resolution structure of the infectious PrP(Sc) state remains unknown, and its analysis largely relies on detergent-based preparations devoid of endogenous ligands. Here we designed polymers that allow isolation of endogenous membrane:protein assemblies in native nanodiscs without exposure to conventional detergents that destabilize protein structures and induce fibrillization. A set of styrene–maleic acid (SMA) polymers including a methylamine derivative facilitated gentle release of the infectious complexes for resolution of multimers, and a thiol-containing version promoted crystallization. Polymer extraction from brain homogenates from Syrian hamsters infected with Hyper prions and WT mice infected with Rocky Mountain Laboratories prions yielded infectious prion nanoparticles including oligomers and microfilaments bound to lipid vesicles. Lipid analysis revealed the brain phospholipids that associate with prion protofilaments, as well as those that are specifically enriched in prion assemblies captured by the methylamine-modified copolymer. A comparison of the infectivity of PrP(Sc) attached to SMA lipid particles in mice and hamsters indicated that these amphipathic polymers offer a valuable tool for high-yield production of intact, detergent-free prions that retain in vivo activity. This native prion isolation method provides an avenue for producing relevant prion:lipid targets and potentially other proteins that form multimeric assemblies and fibrils on membranes.

Bovine spongiform encephalopathy (BSE) is a prion disease of cattle that is caused by the misfolding of the cellular prion protein (PrPC) into an infectious conformation (PrPSc). PrPC is a predominantly α-helical membrane protein that misfolds into a β-sheet rich, infectious state, which has a high propensity to self-assemble into amyloid fibrils. Three strains of BSE prions can cause prion disease in cattle, including classical BSE (C-type) and two atypical strains, named L-type and H-type BSE. To date, there is no detailed information available about the structure of any of the infectious BSE prion strains. In this study, we purified L-type BSE prions from transgenic mouse brains and investigated their biochemical and ultrastructural characteristics using electron microscopy, image processing, and immunogold labeling techniques. By using phosphotungstate anions (PTA) to precipitate PrPSc combined with sucrose gradient centrifugation, a high yield of proteinase K-resistant BSE amyloid fibrils was obtained. A morphological examination using electron microscopy, two-dimensional class averages, and three-dimensional reconstructions revealed two structural classes of L-type BSE amyloid fibrils; fibrils that consisted of two protofilaments with a central gap and an average width of 22.5 nm and one-protofilament fibrils that were 10.6 nm wide. The one-protofilament fibrils were found to be more abundant compared to the thicker two-protofilament fibrils. Both fibrillar assemblies were successfully decorated with monoclonal antibodies against N- and C-terminal epitopes of PrP using immunogold-labeling techniques, confirming the presence of polypeptides that span residues 100–110 to 227–237. The fact that the one-protofilament fibrils contain both N- and C-terminal PrP epitopes constrains molecular models for the structure of the infectious conformer in favour of a compact four-rung β-solenoid fold., Author summary Bovine spongiform encephalopathy (BSE), also called “mad cow disease,” is a deadly neurodegenerative disease in cattle. BSE is caused by PrPSc, which is an aberrantly folded conformer of a normal protein in the host. PrPSc is an infectious protein and also referred to as a prion. BSE prions exist in three variants or strains: C-type BSE prions, which caused the epizootic “mad cow disease” outbreak, and two atypical forms L-type and H-type BSE prions, named according to their migration patterns during gel electrophoresis. For our investigations, we isolated L-type BSE prions from transgenic mouse brains and analyzed these samples using transmission electron microscopy and three-dimensional reconstruction techniques. Our study revealed that L-type BSE prions assemble into one- and two-protofilament containing amyloid fibrils and that the width of the two-protofilament fibrils is approximately twice that of one-protofilament fibrils. In addition, we labeled the L-type BSE fibrils at the ultrastructural level using specific anti-prion protein antibodies that recognize epitopes at both ends of the molecule. Our data agree with the previously proposed four-rung β-solenoid model for the structure of infectious PrPSc.

Hormone replacement medicine such as traditional Chinese medicine has proven to be effective in decreasing the risk of osteoporosis. Mongolian medicine echinops prevents osteoporosis, but its mechanism remains unclear. In this study, we explored the mechanism underlying echinops prevents and treats postmenopausal osteoporosis. Osteoporosis model was established by ovariectomy in rats. Rats were treated to Echinops (16.26, 32.5, or 65 mg/kg/day) by oral gavage for 3 months. Bone mineral density (BMD) was detected by micro-CT detection of left proximal medial metaphyseal tibia. Hematoxylin and eosin (H&E) and toluidine blue O staining were also performed. Serum levels of E2, ALP and testosterone were examined. Bone marrow-derived bone marrow stem cells (BMSCs) were isolated and treated with echinops-containing serum. Estrogen receptors (ER) including ERα and ERβ in bone specimens and BMSCs were detected by qRT-PCR. Cell viability and colon formation of BMSCs were detected. Expressions of ERα, ERβ, AKT, p-AKT, ERK, and p-ERK in BMSCs were detected by western blot. Results showed that echinops significantly increased trabecular interconnectivity, thickness of trabeculae, and connection of trabecula. Echinops significantly increased BMD and E2, but significantly reduced ALP and testosterone in dose-dependent manners. Echinops induced ERα and ERβ in both bone specimens and BMSCs. Echinops enhanced cell viability and ability of colony formation of BMSCs, and increased ERα, ERβ, p-AKT, and p-ERK. Thus, Mongolian echinops reduced bone loss and delayed the occurrence and development of osteoporosis, and increased ERα, ERβ, p-AKT, and P-ERK in BMSCs. These results provide experimental basis for clinical prevention and treatment of postmenopausal osteoporosis by echniops.

Oxygen vacancy defects are highly desirable for photoelectrochemical water splitting reactions of TiO2 nanomaterials because they act as electron donors and thereby enhance the electrical conductivity and charge transport property of TiO2. For TiO2 nanowires reported to date, oxygen vacancies are mainly generated by post-treatment of the as-synthesized nanowires. This comes with a disadvantage that oxygen vacancies are found to form just within a few tens of nanometers at the outer surface of these nanowires, and the photocurrent density is significantly reduced by two to three orders of magnitude when ultraviolet light is filtered out from the AM 1.5G light. Here, we demonstrate, for the first time, the controlled growth of 1D TiO2 nanostructures with different morphologies and with incorporation of oxygen vacancy defects on a Si substrate by a single-step, catalyst-assisted pulsed laser deposition (PLD) method. Photoelectrochemical water splitting measurements under simulated sunlight show that the decorated nanowires exhibit one of the highest photoactivity values in the visible region (>430 nm) reported to date, which represents 87% of the overall photocurrent. The higher activity in the visible region can be attributed to more conductive TiO2 nanostructures (i.e., with a larger amount of oxygen vacancy defects), and the enhanced charge transfer from the nanocrystallites to the core of the decorated nanowires.

We have applied time-resolved THz spectroscopy to probe the transient photoexcited carrier dynamics and THz conductivity in Si nanocrystal films with varying silicon volume filling fractions and nanocrystal sizes on picosecond time scales. The THz conductivity reveals microscopic carrier motion with significant interface scattering within nanocrystals as well as percolative transport between nanocrystals. The time variation of the THz conductivity is analyzed within the framework of the Drude-Smith model, an extension of the Drude model that characterizes carrier localization in nanostructured materials. Below the percolation threshold, transport between nanocrystals is inhibited and photoexcited carriers are localized within individual nanocrystals. These films also exhibit efficient optical emission. In films with Si filling fractions above the percolation threshold, photoluminescence is suppressed and a transition from long-range inter-nanocrystal transport immediately after photoexcitation to increased carrier localization over a 50 ps time scale due to accumulation of charges at interface defect sites is observed.

We show that free-standing silicon quantum dots (QDs) can be photoactivated by blue or UV optical irradiation. The luminescence intensity increases by an order of magnitude for irradiation times of several minutes under moderate optical power. The cut-off energy for photoactivation is between 2.1 and 2.4 eV, not very different from the activation energy for hydrogen dissociation from bulk silicon surfaces. We propose the mechanism for this effect is associated with silicon-hydride bond breaking and the subsequent oxidation of dangling bonds. This phenomenon could be used to “write” luminescent quantum dots into pre-determined arrays.

This paper examines the limits of transmission electron tomography reconstruction methods for a nanocomposite object composed of many closely packed nanoparticles. Two commonly used reconstruction methods in TEM tomography were examined and compared, and the sources of various artefacts were explored. Common visualization methods were investigated, and the resulting “interpretation artefacts” ( i.e., deviations from “actual” particle sizes and shapes arising from the visualization) were determined. Setting a known or estimated nanoparticle volume fraction as a criterion for thresholding does not in fact give a good visualization. Unexpected effects associated with common built-in image filtering methods were also found. Ultimately, this work set out to establish the common problems and pitfalls associated with electron beam tomographic reconstruction and visualization of samples consisting of closely spaced nanoparticles.

Here we report a new sample preparation method for three-dimensional electron tomography. The method uses the standard film deposition and focused ion beam (FIB) methods to significantly reduce the problems arising from the projected sample thickness at high tilt angles. The method can be used to prepare tomography samples that can be imaged up to a ±75° tilt range which is sufficient for many practical applications. The method can minimize the problem of Ga+ contamination, as compared to the case of FIB preparation of rod-shaped samples, and provides extended thin regions for standard 2D projection analyses. Microsc. Res. Tech. 75:1165–1169, 2012. © 2012 Wiley Periodicals, Inc.

We have applied time-resolved terahertz (THz) spectroscopy to probe ultrafast conduction dynamics of photoexcited carriers in silicon nanocrystal films with a wide range of nanocrystal sizes and concentrations. The picosecond THz conductivity reveals microscopic photocarrier motion with significant interface scattering within the nanocrystals, as well as percolative transport between nanocrystals. In films with silicon filling fractions above the percolation threshold, we observe a transition from long-range internanocrystal transport immediately after photoexcitation to increased carrier localization over a 50-ps time scale due to accumulation of charges at interface defect sites. However, in films with silicon filling fractions below the percolation threshold, transport between nanocrystals is strongly suppressed at all times. Finally, we estimate effective carrier diffusion lengths of 60 to 130 nm for the silicon nanocrystal composites with silicon filling fractions above the percolation threshold, making such films promising candidates for active layers in photovoltaic devices. © 2011 American Physical Society.

Imaging the spatial distribution of silicon nanocrystals (Si-NCs) and erbium ion clusters can assist in the development of light-emitting erbium-doped silicon nanocomposites. We applied simultaneous energy-filtered and high-angle annular dark field imaging in the scanning transmission electron microscopy (STEM) mode; the former method images the Si NCs and the latter is sensitive to the high atomic number of the Er3+ ions. Both methods were performed simultaneously so as to avoid relative image drift. In Er-doped Si nano-composites, we find that the Er ions are not uniformly distributed in the matrix: instead, they form clusters that appear in projection images to decorate the boundaries of the Si-NCs. This structure may develop during sample annealing, due to the low solubility of Er in the forming Si clusters. Although multi-detector simultaneous imaging is a good way to avoid nanometer-scale image drift that could otherwise conceal the nanoscale spatial relationship between Si-NCs and Er clusters, an additional difficulty relates to the projection imaging methods. Essentially, it is hard to obtain spatial information parallel to the electron beam direction, so where there is apparent overlap we cannot ascertain whether an Er cluster (for example) lies above, below, or inside a given Si-NC. Therefore, we also report on initial electron beam tomography investigations whose goal is ultimately to generate methods for obtaining the Er and Si cluster distribution in 3D. The results can lead to improved understanding of the sensitization mechanism and optimization for Er-doped silicon nanocomposites; the clustered nature of the Er ions near the Si NCs is certainly undesirable and may explain the typically short Er3+ photoluminescence (PL) lifetimes (compared to Er-doped silica) and the difficulty in reliably observing stimulated emission phenomena (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Study design Eighty newly-hatched White leghorn and forty-two newlyhatched Mountain Hubbard chickens were divided equally into control and experimental groups. The experimental chickens underwent pinealectomy. All chickens were observed for five weeks during which time radiographs were taken weekly to assess the development of scoliosis. Weight and spinal length measurements were also gathered.

Nanoscale material manipulation is the key to increasing solar light harvesting and photon-to-electron conversion efficiency (PCE) for an organic–inorganic photovoltaic system. Many SnO2 1D nanostructures, including nanowires and nanobelts, have been employed because of their potential of enhancing the charge collection properties of DSSCs by eliminating losses caused by grain boundary scattering of carriers in nanoparticle-based DSSCs. Here, a new approach to growing hierarchical 1D SnO2 nanostructured layer by catalyst-assisted pulsed laser deposition after introducing NiO into the SnO2 target is reported, and a plausible growth mechanism to describe the observed hierarchical nanostructures is presented. A remarkable improvement in the solar cell performance, including open circuit voltage, short circuit current density, fill factor, and PCE, by simple surface modification of the hierarchical SnO2 nanostructured photoanode is further demonstrated. Surface passivation is achieved on the as-deposited hierarchical SnO2 nanostructures by dip coating with an MgO passivation layer of appropriately optimized thickness. Such an insulating layer is found to effectively reduce the recombination process caused by the higher electron mobility of SnO2 photoanode nanostructures. Compared with a pristine SnO2 nanobelt photoanode, a tenfold enhancement in their PCE (to 4.14%) has been observed for MgO-passivated hierarchical SnO2 nanostructures.

We use terahertz pulses to probe ultrafast carrier dynamics in InGaAs quantum dot chains. The terahertz polarization is used to explore the anisotropy in the photoconductive response as a function of temperature and excitation density.

Electron tomography (ET) in a TEM has been widely used to characterize materials at sub-10 nm spatial resolution. The first example of tomographic imaging in an electron microscope was reported four decades ago. However, due to the fast development of processing capacity of modern computers it is only in the past few years that ET in (scanning) transmission electron microscopy ((S)TEM) has become a more viable option for investigating the morphologies, spatial distribution and chemical compositions of nanostructures., Proceedings of Microscopy & Microanalysis 2011, August 7-11, 2011, Nashville, Tennessee

Electrodeposited Au–Pt alloy nanoparticles supported on ITO-glass substrates have been used as a model catalyst to study the electro-oxidation of methanol (0.5 M) in a KOH (0.5 M) electrolyte. Using cyclic voltammetry, we show that the Au–Pt alloy nanoparticles exhibit a significantly higher catalytic activity than the Pt nanoparticles, while the Au nanoparticles show no catalytic affinity toward electro-oxidation of methanol. The Au–Pt alloy nanoparticles are also found to be catalytically more reactive than bimetallic Au-core Pt-shell and Pt-core Au-shell nanoparticles. We further show that these Au–Pt alloy nanoparticles working in alkaline solution could act as an amperometric sensor for the determination of alcohol concentration. The exceptional performance of this nanoalloy sensor, including its short response time (2 s), relatively large linear range (1–11 mM), low detection limit (0.1 mM), high sensitivity (0.043 mA cm−2 mM−1) and long-term stability (over 90 days), are also characterized. The present nanoalloy sensor also has the lowest working potential (0.25 V), making it less prone to an interference effect.

Pinealectomy in young chickens consistently results in scoliosis, which has many characteristics similar to those seen in adolescent idiopathic scoliosis. The mechanism underlying this phenomenon remains a mystery and it is not yet entirely clear whether some unidentified aspect of the extensive surgery is the major factor rather than the removal of the pineal gland. Four different types of pinealectomy surgery were performed on young chickens as well as deliberate damage to the cerebral cortex which simulated the extreme of any accidental damage that might occur during surgery. Scoliosis was assessed from weekly radiographs. No differences in incidence of scoliosis, degree of severity, or pattern of curve development were observed for any of the experimental groups when compared with controls. In all groups approximately 55% of the chickens developed scoliosis that progressed rapidly. Different pinealectomy procedures and deliberate damage to the cerebral cortex produce scoliosis in young chickens with the same incidence and characteristics. This suggests strongly that the mechanism behind the phenomenon is due to the removal of the pineal gland and not some artifact of the extensive surgery. The pinealectomy model in young chickens is proving to be a good model for studying AIS in humans. An understanding of the mechanism underlying this phenomenon has the potential to provide further insights into the etiology of AIS and can lead to the development of novel treatment methods. Microsc. Res. Tech. 53:81–86, 2001. © 2001 Wiley-Liss, Inc.

not Available.