Electron microscopy of prefibrillar structures and amyloid fibrils
Odense University, Denmark. Methods in Enzymology
(Impact Factor: 2.09).
02/1999; 309:491-6. DOI: 10.1016/S0076-6879(99)09033-3
Several techniques, such as X-ray crystallography, light scattering, fluorescence spectrometry, size exclusion chromatography, atomic force microscopy, and transmission electron microscopy, have been employed in studies of structural intermediates of fibril formation and fibrillar assembly of amyloid proteins. Electron microscopy, with a resolution of approximately 2 nm, offers a useful technique for the ultrastructural characterization of preprotofilaments, protofilaments, and mature fibrils formed during in vitro fibrillogenesis. For contrast enhancement of specimens, negative staining is applied. This chapter outlines the methodology used in laboratories for electron microscopic examination of negatively stained prefibrillar structures and amyloid fibrils. The Aβ-peptide used influences the kinetics of the fibril formation. This chapter uses Aβ1–42 (Bachem, Bubendorf, Switzerland), which forms fibrils within a few hours of incubation at 37°. In order to decelerate the fibril formation enabling it to investigate early intermediates and prefibrillar structures, this chapter has performed the in vitro studies at low concentrations of Aβ1–42 (170 μg/ml), as the kinetics of fibril formation is highly concentration dependent.
Available from: Oxana Galzitskaya
- "The morphology of fibrils in water (pH 3.0) obtained by us is totally consistent with the previously obtained data . "
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ABSTRACT: The aim of this study was to investigate the process of amyloidogenesis of amyloid-β (Aβ)42 peptide, by means of fluorescence spectroscopy, electron microscopy, X-ray diffraction, and mass spectrometry. It has been repeatedly reported in the literature that the process of fibril formation by Aβ 42 peptide depends considerably not only upon the specific conditions (ionic conditions, pH, temperature, mixing, etc.), as well as the manufacturing route (synthetic or recombinant), but also on the methods of synthesis and purification. We have, for the first time, systematically analyzed samples of Aβ 42 peptide supplied by five different companies (Anaspec, Invitrogen, Enzo, Sigma-Aldrich, and SynthAssist) and obtained evidence of significant variability, including lot to lot variations. All studied samples formed amyloid-like fibrils at pH3-6, and the fibrils contained cross-β structures. Samples from Anaspec, Invitrogen, and Enzo formed one particular type of amyloid-like fibrils, while the samples from Sigma-Aldrich and SynthAssist formed another distinct type of fibrils. The observed polymorphism emphasizes the capacity of the Aβ 42 peptide to act as a prion agent with varying structural characteristics. The presented data have allowed us to propose a possible mechanism of formation of amyloid-like fibrils.
Available from: Enrique García-Hernández
- "The presence of disordered fibers (observed mainly in controlled pH) could be due to globular protein elements forming complex macro-aggregates. Similar fibers structures have been observed previously [78,79]. In addition, the differences in IBs size probably are due to differences in nucleation and IB growth properties during formation, as well the host proteins that interact with them. "
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Inclusion bodies (IBs) are aggregated proteins that form clusters when protein is overexpressed in heterologous expression systems. IBs have been considered as non-usable proteins, but recently they are being used as functional materials, catalytic particles, drug delivery agents, immunogenic structures, and as a raw material in recombinant therapeutic protein purification. However, few studies have been made to understand how culture conditions affect the protein aggregation and the physicochemical characteristics that lead them to cluster. The objective of our research was to understand how pH affects the physicochemical properties of IBs formed by the recombinant sphingomyelinase-D of tick expressed in E. coli BL21-Gold(DE3) by evaluating two pH culture strategies.ResultsUncontrolled pH culture conditions favored recombinant sphingomyelinase-D aggregation and IB formation. The IBs of sphingomyelinase-D produced under controlled pH at 7.5 and after 24 h were smaller (<500 nm) than those produced under uncontrolled pH conditions (>500 nm). Furthermore, the composition, conformation and ß-structure formation of the aggregates were different. Under controlled pH conditions in comparison to uncontrolled conditions, the produced IBs presented higher resistance to denaturants and proteinase-K degradation, presented ß-structure, but apparently as time passes the IBs become compacted and less sensitive to amyloid dye binding.Conclusions
The manipulation of the pH has an impact on IB formation and their physicochemical characteristics. Particularly, uncontrolled pH conditions favored the protein aggregation and sphingomyelinase-D IB formation. The evidence may lead to find methodologies for bioprocesses to obtain biomaterials with particular characteristics, extending the application possibilities of the inclusion bodies.
Available from: Ramalingam Kirubagaran
- "All reagents used in peptide synthesis pentafluorophenol (Spectrochem Pvt. Ltd., Mumbai), N,N-dicyclohexyl carbodiimide (Sigma-Aldrich), Fmoc-AA (Novabiochem), HOBt (Sigma-Aldrich) and TFA (Sigma-Aldrich) were of the purest analytical grade. The Aβ peptide fibrils were formed by solubilizing the peptide in sterile double distilled (DD) water (1 mg/ml) and incubated for 24 h at 37 °C (Nielsen et al., 1999). The protofibrillar form thus obtained was used fresh for the present study. "
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ABSTRACT: Oxidative stress is one of the hypothesized pathogenic mechanisms for neurodegenerative diseases, including Alzheimer's disease (AD); numerous studies suggest that Abeta is toxic to neurons by free radical mediated mechanism. A constant feature in AD brain is selective neuronal loss, accompanied by dysfunction of several neurotransmitter systems, such as cholinergic, serotoninergic and noradrenergic systems. In the present study, we studied the neuroprotective role of melatonin against amyloid protofibrils and the toxicity of protofibrils on serotoninergic and noradrenergic systems. Mice were divided into four groups (n=8 each), control, Scrambles Abeta(35-25) treated, Abeta(25-35) injected, and melatonin treated. A single dose of Abeta(25-35) (25 microg) was administered to mice via intraperitoneal injection. Melatonin (50 mg/kg body weight) was administered intraperitoneally for 3 days to the Abeta(25-35) injected mice. Control mice received only physiological saline and Scrambles receives Abeta(35-25) single intraperitoneal injection of 25 microg of Abeta(35-25). Our study showed that melatonin significantly reduces reactive oxygen species (ROS) production in the astrocytes, lymphocytes and hepatocytes of Abeta injected mice by increasing the levels of scavenging enzymes, SOD, catalase and GSH when compared to the untreated group. Immunohistochemistry study reveals that melatonin prevents the activation of GFAP in neocortex and transcription factor NF-kappaB in liver and neocortex of Abeta injected mice. It also prevents the elevation of dopamine depletion and its degradation products. Thus, while melatonin may be a potential therapeutic agent in the prevention of oxidative stress associated with Abeta and AD, it can also prevent dopamine turnover induced by Abeta.
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