384 research outputs found
Exceptional rigidity and biomechanics of amyloid revealed by 4D electron microscopy
Amyloid is an important class of proteinaceous material because of its close association with protein misfolding disorders such as Alzheimer’s disease and type II diabetes. Although the degree of stiffness of amyloid is critical to the understanding of its pathological and biological functions, current estimates of the rigidity of these β-sheet–rich protein aggregates range from soft (10^8 Pa) to hard (10^(10) Pa) depending on the method used. Here, we use time-resolved 4D EM to directly and noninvasively measure the oscillatory dynamics of freestanding, self-supporting amyloid beams and their rigidity. The dynamics of a single structure, not an ensemble, were visualized in space and time by imaging in the microscope an amyloid–dye cocrystal that, upon excitation, converts light into mechanical work. From the oscillatory motion, together with tomographic reconstructions of three studied amyloid beams, we determined the Young modulus of these highly ordered, hydrogen-bonded β-sheet structures. We find that amyloid materials are very stiff (10^9 Pa). The potential biological relevance of the deposition of such a highly rigid biomaterial in vivo are discussed
Nanomechanics and intermolecular forces of amyloid revealed by four-dimensional electron microscopy
The amyloid state of polypeptides is a stable, highly organized
structural form consisting of laterally associated β-sheet protofilaments
that may be adopted as an alternative to the functional,
native state. Identifying the balance of forces stabilizing amyloid is
fundamental to understanding the wide accessibility of this state
to peptides and proteins with unrelated primary sequences, various
chain lengths, and widely differing native structures. Here, we
use four-dimensional electron microscopy to demonstrate that the
forces acting to stabilize amyloid at the atomic level are highly
anisotropic, that an optimized interbackbone hydrogen-bonding
network within β-sheets confers 20 times more rigidity on the
structure than sequence-specific sidechain interactions between
sheets, and that electrostatic attraction of protofilaments is only
slightly stronger than these weak amphiphilic interactions. The
potential biological relevance of the deposition of such a highly
anisotropic biomaterial in vivo is discussed
Prioritizing surveillance activities for certification of yaws eradication based on a review and model of historical case reporting
BACKGROUNDt: The World Health Organization
(WHO) has targeted yaws for global eradication. Eradication
requires certification that all countries are yaws-free. While
only 14 Member States currently report cases to WHO, many more
are known to have a history of yaws and some of them may have
ongoing transmission. We reviewed the literature and developed a
model of case reports to identify countries in which passive
surveillance is likely to find and report cases if transmission
is still occurring, with the goal of reducing the number of
countries in which more costly active surveillance will be
required. METHODSt: We reviewed published and
unpublished documents to extract data on the number of yaws
cases reported to WHO or appearing in other literature in any
year between 1945 and 2015. We classified countries as: a)
having interrupted transmission; b) being currently endemic; c)
being previously endemic (current status unknown); or d) having
no history of yaws. We constructed a panel dataset for the years
1945-2015 and ran a regression model to identify factors
associated with some countries not reporting cases during
periods when there was ongoing (and documented) transmission.
For previously endemic countries whose current status is
unknown, we then estimated the probability that countries would
have reported cases if there had in fact been transmission in
the last three years (2013-2015)." - Label: RESULTS content:
Yaws has been reported in 103 of the 237 countries and areas
considered. 14 Member States and 1 territory (Wallis and Futuna
Islands) are currently endemic. 2 countries are believed to have
interrupted transmission. 86 countries and areas are previously
endemic (current status unknown). Reported cases peaked in the
1950s, with 55 countries reporting at least one case in 1950 and
a total of 2.35 million cases reported in 1954. Our regression
model suggests that case reporting during periods of ongoing
transmission is positively associated with socioeconomic
development and, in the short-term, negatively associated with
independence. We estimated that for 66 out of the 86 previously
endemic countries whose current status is unknown, the
probability of reporting cases in the absence of active
surveillance is less than 50%. DISCUSSION:
Countries with a history of yaws need to be prioritized so that
international resources for global yaws eradication may be
deployed efficiently. Heretofore, the focus has been on mass
treatment in countries currently reporting cases. It is also
important to undertake surveillance in the 86 previously endemic
countries for which the current status is unknown. Within this
large and diverse group, we have identified a group of 20
countries with more than a 50% probability of reporting cases in
the absence of active surveillance. For the other 66 countries,
international support for active surveillance will likely be
required
4D Cryo-Electron Microscopy of Proteins
Cryo-electron microscopy is a form of
transmission electron microscopy that has been used to
determine the 3D structure of biological specimens in the
hydrated state and with high resolution. We report the
development of 4D cryo-electron microscopy by integrating
the fourth dimension, time, into this powerful
technique. From time-resolved diffraction of amyloid
fibrils in a thin layer of vitrified water at cryogenic
temperatures, we were able to detect picometer movements
of protein molecules on a nanosecond time scale.
Potential future applications of 4D cryo-electron microscopy
are numerous, and some are discussed here
UV Absorption Lines from High-Velocity Gas in the Vela Supernova Remnant: New insights from STIS Echelle Observations of HD72089
The star HD72089 is located behind the Vela supernova remnant and shows a
complex array of high and low velocity interstellar absorption features arising
from shocked clouds. A spectrum of this star was recorded over the wavelength
range 1196.4 to 1397.2 Angstroms at a resolving power lambda/Delta lambda =
110,000 and signal-to-noise ratio of 32 by STIS on the Hubble Space Telescope.
We have identified 7 narrow components of C I and have measured their relative
populations in excited fine-structure levels. Broader features at heliocentric
velocities ranging from -70 to +130 km/s are seen in C II, N I, O I, Si II, S
II and Ni II. In the high-velocity components, the unusually low abundances of
N I and O I, relative to S II and Si II, suggest that these elements may be
preferentially ionized to higher stages by radiation from hot gas immediately
behind the shock fronts.Comment: 11 pages, 2 figures, Latex. Submitted for the special HST ERO issue
of the Astrophysical Journal Letter
In-cell NMR characterization of the secondary structure populations of a disordered conformation of α-Synuclein within E. coli cells
α-Synuclein is a small protein strongly implicated in the pathogenesis of Parkinson’s disease and related neurodegenerative disorders. We report here the use of in-cell NMR spectroscopy to observe directly the structure and dynamics of this protein within E. coli cells. To improve the accuracy in the measurement of backbone chemical shifts within crowded in-cell NMR spectra, we have developed a deconvolution method to reduce inhomogeneous line broadening within cellular samples. The resulting chemical shift values were then used to evaluate the distribution of secondary structure populations which, in the absence of stable tertiary contacts, are a most effective way to describe the conformational fluctuations of disordered proteins. The results indicate that, at least within the bacterial cytosol, α-synuclein populates a highly dynamic state that, despite the highly crowded environment, has the same characteristics as the disordered monomeric form observed in aqueous solution
Metastability of native proteins and the phenomenon of amyloid formation
An experimental determination of the thermodynamic stabilities of a series of amyloid fibrils reveals that this structural form is likely to be the most stable one that protein molecules can adopt even under physiological conditions. This result challenges the conventional assumption that functional forms of proteins correspond to the global minima in their free energy surfaces and suggests that living systems are conformationally as well as chemically metastable. © 2011 American Chemical Society
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Calibration of the charge and energy loss per unit length of the MicroBooNE liquid argon time projection chamber using muons and protons
We describe a method used to calibrate the position- and time-dependent response of the MicroBooNE liquid argon time projection chamber anode wires to ionization particle energy loss. The method makes use of crossing cosmic-ray muons to partially correct anode wire signals for multiple effects as a function of time and position, including cross-connected TPC wires, space charge effects, electron attachment to impurities, diffusion, and recombination. The overall energy scale is then determined using fully-contained beam-induced muons originating and stopping in the active region of the detector. Using this method, we obtain an absolute energy scale uncertainty of 2% in data. We use stopping protons to further refine the relation between the measured charge and the energy loss for highly-ionizing particles. This data-driven detector calibration improves both the measurement of total deposited energy and particle identification based on energy loss per unit length as a function of residual range. As an example, the proton selection efficiency is increased by 2% after detector calibration
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Reconstruction and measurement of (100) MeV energy electromagnetic activity from π0 arrow γγ decays in the MicroBooNE LArTPC
We present results on the reconstruction of electromagnetic (EM) activity from photons produced in charged current νμ interactions with final state π0s. We employ a fully-automated reconstruction chain capable of identifying EM showers of (100) MeV energy, relying on a combination of traditional reconstruction techniques together with novel machine-learning approaches. These studies demonstrate good energy resolution, and good agreement between data and simulation, relying on the reconstructed invariant π0 mass and other photon distributions for validation. The reconstruction techniques developed are applied to a selection of νμ + Ar → μ + π0 + X candidate events to demonstrate the potential for calorimetric separation of photons from electrons and reconstruction of π0 kinematics
A qualitative study of how people with severe mental illness experience living in sheltered housing with a private fully equipped apartment
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