285 research outputs found
Cholesterol facilitates interactions between α-synuclein oligomers and charge-neutral membranes
No full textOligomeric species formed during α-synuclein fibrillation are suggested to be membrane-disrupting agents, and have been associated with cytotoxicity in Parkinson's disease. The majority of studies, however, have revealed that the effect of α-synuclein oligomers is only noticeable on systems composed of anionic lipids, while the more physiologically relevant zwitterionic lipids remain intact. We present experimental evidence for significant morphological changes in zwitterionic membranes containing cholesterol, induced by α-synuclein oligomers. Depending on the lipid composition, model membranes are either unperturbed, disrupt, or undergo dramatic morphological changes and segregate into structurally different components, which we visualize by 2-photon fluorescence microscopy and generalized polarization analysis using the fluorescent probe Laurdan. Our results highlight the crucial role of cholesterol for mediating interactions between physiologically relevant membranes and α-synuclein
Analysis of biostructural changes, dynamics, and interactions – Small-angle X-ray scattering to the rescue
No full textAbstractSolution small angle X-ray scattering from biological macromolecules (BioSAXS) plays an increasingly important role in biostructural research. The analysis of complex protein mixtures, dynamic equilibriums, intrinsic disorder and evolving structural processes is facilitated by SAXS data, either in stand-alone applications, or with SAXS taking a prominent role in hybrid biostructural analysis. This is not the least due to the significant advances in both hardware and software that have taken place in particular at the large-scale facilities. Here, recent developments and the future potential of BioSAXS are reviewed, exemplified by numerous examples of elegant applications to challenging systems
Ethanol Controls the Self-Assembly and Mesoscopic Properties of Human Insulin Amyloid Spherulites
No full textProtein self-assembly
into amyloid fibrils or highly hierarchical
superstructures is closely linked to neurodegenerative pathologies
as Alzheimer’s and Parkinson’s diseases. Moreover, protein
assemblies also emerged as building blocks for bioinspired nanostructured
materials. In both the above mentioned fields, the main challenge
is to control the growth and properties of the final protein structure.
This relies on a more fundamental understanding of how interactions
between proteins can determine structures and functions of biomolecular
aggregates. Here, we identify a striking effect of the hydration of
the single human insulin molecule and solvent properties in controlling
hydrophobicity/hydrophilicity, structures, and morphologies of a superstructure
named spherulite, observed in connection to Alzheimer’s disease.
Depending on the presence of ethanol, such structures can incorporate
fluorescent molecules with different physicochemical features and
span a range of mechanical properties and morphologies. A theoretical
model providing a thorough comprehension of the experimental data
is developed, highlighting a direct connection between the intimate
physical protein–protein interactions, the growth, and the
properties of the self-assembled superstructures. Our findings indicate
structural variability as a general property for amyloid-like aggregates
and not limited to fibrils. This knowledge is pivotal not only for
developing effective strategies against pathological amyloids but
also for providing a platform to design highly tunable biomaterials,
alternative to elongated protein fibrils
Differential effects of endurance training and weight loss on plasma adiponectin multimers and adipose tissue macrophages in younger, moderately overweight men
No full textCALL FOR PAPERS: Integrative and Translational Physiology: Inflammation
and Immunity in Organ System PhysiologyObese individuals are characterized by low circulating adiponectin concentrations and an increased number of macrophages in adipose tissue, which is believed to be causally associated with chronic low-grade inflammation and insulin resistance. Regular physical exercise decreases overall morbidity in obese subjects, which may be due to modulations of inflammatory pathways. In this randomized clinical trial we investigated the separate effects of endurance training-induced weight loss, diet-induced weight loss, and endurance training per se (without weight loss) on plasma adiponectin multimer composition (Western blotting) and adipose tissue macrophage content (immunohistochemistry) in young, moderately overweight men. Weight loss and endurance training per se decreased whole body fat percentage in an additive manner. No intervention-induced changes were observed for plasma total adiponectin. Surprisingly, endurance training, irrespectively of any associated weight loss, shifted the adiponectin multimer distribution toward a lower molecular weight (21% decrease in HMW/LMW, P = 0.015), whereas diet-induced weight loss shifted the distribution toward a higher molecular weight (42% increase in HMW/MMW, P < 0.001). Furthermore, endurance training per se increased the number of anti-inflammatory CD163⁺ macrophages [from 12.7 ± 2.1 (means ± SE) to 16.1 ± 3.1 CD163⁺ cells/100 adipocytes, P = 0.013], whereas diet-induced weight loss tended to decrease CD68⁺ macrophages in subcutaneous abdominal adipose tissue. Thus regular physical exercise influences systemic and adipose tissue inflammatory pathways differently than diet-induced weight loss in younger, moderately overweight men. Our data suggest that some of the health benefits of a physically active lifestyle may occur through modulations of anti- rather than pro-inflammatory pathways in young, overweight men.Pernille Auerbach, Pernille Nordby, Line Q. Bendtsen, Jesper L. Mehlsen, Smita K. Basnet, Henrik Vestergaard, Thorkil Ploug, Bente Stallknech
Neurostereology
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
Trifluoroethanol modulates α-synuclein amyloid-like aggregate formation, stability and dissolution
No full textThe conversion of proteins into amyloid fibrils and other amyloid-like aggregates is closely connected to the onset of a series of age-related pathologies. Upon changes in environmental conditions, amyloid-like aggregates may also undergo disassembly into oligomeric aggregates, the latter being recognized as key effectors in toxicity. This indicates new possible routes for in vivo accumulation of toxic species. In the light of the recognized implication of α-Synuclein (αSN) in Parkinson's disease, we present an experimental study on supramolecular assembly of αSN with a focus on stability and disassembly paths of such supramolecular aggregate species. Using spectroscopic techniques, two-photon microscopy, small-angle X-ray scattering and atomic force microscopy, we report evidences on how the stability of αSN amyloid-like aggregates can be altered by changing solution conditions. We show that amyloid-like aggregate formation can be induced at high temperature in the presence of trifluoroethanol (TFE). Moreover, sudden disassembly or further structural reorganisation toward higher hierarchical species can be induced by varying TFE concentration. Our results may contribute in deciphering fundamental mechanisms and interactions underlying supramolecular clustering/dissolution of αSN oligomers in cells
Protein/Lipid Coaggregates are Formed During α-Synuclein-Induced Disruption of Lipid Bilayers
No full textAmyloid formation is associated with neurodegenerative diseases such as Parkinson’s disease (PD). Significant α-synuclein (αSN) deposition in lipid-rich Lewy bodies is a hallmark of PD. Nonetheless, an unraveling of the connection between neurodegeneration and amyloid fibrils, including the molecular mechanisms behind potential amyloid-mediated toxic effects, is still missing. Interaction between amyloid aggregates and the lipid cell membrane is expected to play a key role in the disease progress. Here, we present experimental data based on hybrid analysis of two-photon-microscopy, solution small-angle X-ray scattering and circular dichroism data. Data show in real time changes in liposome morphology and stability upon protein addition and reveal that membrane disruption mediated by amyloidogenic αSN is associated with dehydration of anionic lipid membranes and stimulation of protein secondary structure. As a result of membrane fragmentation, soluble αSN:-lipid coaggregates are formed, hence, suggesting a novel molecular mechanism behind PD amyloid cytotoxicity
Unlocked Concanavalin A Forms Amyloid-like Fibrils from Coagulation of Long-lived "Crinkled'' Intermediates
No full textUnderstanding the early events during amyloid aggregation processes is crucial to single out the involved molecular mechanisms and for designing ad hoc strategies to prevent and reverse amyloidogenic disorders. Here, we show that, in conditions in which the protein is positively charged and its conformational flexibility is enhanced, Concanavalin A leads to fibril formation via a non-conventional aggregation pathway. Using a combination of light scattering, circular dichroism, small angle X-ray scattering, intrinsic (Tryptophan) and extrinsic (ANS) fluorescence and confocal and 2-photon fluorescence microscopy we characterize the aggregation process as a function of the temperature. We highlight a multi-step pathway with the formation of an on-pathway long-lived intermediate and a subsequent coagulation of such "crinkled'' precursors into amyloid-like fibrils. The process results in a temperature-dependent aggregation-coagulation pathway, with the late phase of coagulation determined by the interplay between hydrophobic and electrostatic forces. Our data provide evidence for the complex aggregation pathway for a protein with a highly flexible native conformation. We demonstrate the possibility to generate a long-lived intermediate whose proportion and occurrence are easily tunable by experimental parameters (i.e. temperature). As a consequence, in the case of aggregation processes developing through well-defined energy barriers, our results can open the way to new strategies to induce more stable in vitro on-pathway intermediate species through a minute change in the initial conformational flexibility of the protein. This will allow isolating and experimentally studying such transient species, often indicated as relevant in neurodegenerative diseases, both in terms of structural and cytotoxic properties
SAS-Based Studies of Protein Fibrillation
No full textProtein fibrillation is associated with a number of fatal amyloid diseases (e.g. Alzheimer's and Parkinson's diseases). From a structural point of view, the aggregation process starts from an ensemble of native states that convert into transiently formed oligomers, higher order assemblies and protofibrils and, finally, fibrils. The different species exist in equilibrium in solution leading to a high degree of sample heterogeneity. It is impossible to physically isolate any single species for structural analysis: separation will alter the equilibrium and potentially cause structural changes.Small angle scattering is an optimal method for structural studies of the fibrillation process in order to further the knowledge of the associated diseases. The recorded scattering data include the scattering contribution of all the species in solution and must be decomposed to enable structural modeling of the individual components involved during the fibrillation, notably without physical separation of the species. In this chapter we explain how to optimize a small angle scattering analysis of the fibrillation process and the basic principles behind analysis of the data. We include several practical tips and highlight existing reports, exemplifying the wealth of information that can be derived from the method.</p
Methods for structural characterization of prefibrillar intermediates and amyloid fibrils
No full textAbstractProtein fibrillation is first and foremost a structural phenomenon. Adequate structural investigation of the central conformational individuals of the fibrillation process is however exceedingly difficult. This is due to the nature of the process, which may be described as a dynamically evolving equilibrium between a large number of structural species. These are furthermore of highly diverging sizes and present in very uneven amounts and timeframes. Different structural methods have different strengths and limitations. These, and in particular recent advances within solution analysis of the undisturbed equilibrium using small angle X-ray scattering, are reviewed here
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