Search results for "electron microscopy"
showing 10 items of 706 documents
Structure of Mega-Hemocyanin Reveals Protein Origami in Snails
2014
SummaryMega-hemocyanin is a 13.5 MDa oxygen transporter found in the hemolymph of some snails. Similar to typical gastropod hemocyanins, it is composed of 400 kDa building blocks but has additional 550 kDa subunits. Together, they form a large, completely filled cylinder. The structural basis for this highly complex protein packing is not known so far. Here, we report the electron cryomicroscopy (cryo-EM) structure of mega-hemocyanin complexes from two different snail species. The structures reveal that mega-hemocyanin is composed of flexible building blocks that differ in their conformation, but not in their primary structure. Like a protein origami, these flexible blocks are optimally pac…
Antibody inhibition of the transcriptase activity of the rotavirus DLP: a structural view.
2001
On entering the host cell the rotavirus virion loses its outer shell to become a double-layered particle (DLP). The DLP then transcribes the 11 segments of its dsRNA genome using its own transcriptase complex, and the mature mRNA emerges along the 5-fold axis. In order to better understand the transcription mechanism and the role of VP6 in transcription we have studied three monoclonal antibodies against VP6: RV-238 which inhibits the transcriptase activity of the DLP; and RV-133 and RV-138 which have no effect on transcription. The structures obtained by cryo-electron microscopy of the DLP/Fab complexes and by X-ray crystallography of the VP6 trimer and the VP6/Fab-238 complex have been co…
Structure of a molluscan hemocyanin didecamer (HtH1 from Haliotis tuberculata) at 12 Å resolution by cryoelectron microscopy
2000
A 12 A resolution three-dimensional density map of the Haliotis tuberculata hemocyanin type 1 (HtH1) didecamer has been obtained by cryoelectron microscopy of unstained molecules and angular reconstitution. The dyad symmetry of the 8 MDa D5 HtH1 didecamer, formed by the pairing of two asymmetric 4 MDa ring-like C5 decamers, is emphasised. The major and minor surface helical grooves of the didecamer are well defined, in agreement with earlier data on molluscan hemocyanins. The location of the obliquely orientated repeating unit, a subunit dimer, within the decamer has been defined. Following interactive extraction of this dimer, several new structural features of the dimer and of the subunit…
Comparative 11A structure of two molluscan hemocyanins from 3D cryo-electron microscopy
2006
Abstract Hemocyanins are giant extracellular proteins that transport oxygen in the hemolymph of many molluscs. Molluscan hemocyanins are cylindrical decamers or didecamers of a 350–400 kDa subunit that contains seven or eight different covalently linked globular functional units (FUs), arranged in a linear manner. Each FU carries a single copper active site and reversibly binds one dioxygen molecule. As a consequence, the decamer can carry up to 70 or 80 O 2 molecules. Although complete sequence information is now available from several molluscan hemocyanins, many details of the quaternary structure are still unclear, including the topology of the 10 subunits within the decamer. Here we sho…
The C-terminal rod 2 fragment of filamin A forms a compact structure that can be extended
2012
Filamins are large proteins that cross-link actin filaments and connect to other cellular components. The C-terminal rod 2 region of FLNa (filamin A) mediates dimerization and interacts with several transmembrane receptors and intracellular signalling adaptors. SAXS (small-angle X-ray scattering) experiments were used to make a model of a six immunoglobulin-like domain fragment of the FLNa rod 2 (domains 16–21). This fragment had a surprising three-branched structural arrangement, where each branch was made of a tightly packed two-domain pair. Peptides derived from transmembrane receptors and intracellular signalling proteins induced a more open structure of the six domain fragment. Mutagen…
Structural mechanism of signal transduction in a phytochrome histidine kinase
2022
AbstractPhytochrome proteins detect red/far-red light to guide the growth, motion, development and reproduction in plants, fungi, and bacteria. Bacterial phytochromes commonly function as an entrance signal in two-component sensory systems. Despite the availability of three-dimensional structures of phytochromes and other two-component proteins, the conformational changes, which lead to activation of the protein, are not understood. We reveal cryo electron microscopy structures of the complete phytochrome from Deinoccocus radiodurans in its resting and photoactivated states at 3.6 Å and 3.5 Å resolution, respectively. Upon photoactivation, the photosensory core module hardly changes its ter…
On the origin of controlled anisotropic growth of monodisperse gold nanobipyramids
2021
We elucidate the crucial role of the cetyl trimethylammonium bromide (CTAB) surfactant in the anisotropic growth mechanism of gold nano-bipyramids, nano-objects with remarkable optical properties and high tunability. Atomistic molecular dynamics simulations predict different surface coverages of the CTAB (positively charged) heads and their (bromide) counterions as function of the gold exposed surfaces. High concentration of CTAB surfactant promotes formation of gold nanograins in solution that work as precursors for the smooth anisotropic growth of more elongated nano-bipyramidal objects. Nanobipyramids feature higher index facets with respect to nanorods, allowing higher CTAB coverages th…
The influence of the raw material and production method on the morphology, microstructure, chemical and phase composition of tetrabasic lead sulfate …
1992
Abstract Tetrabasic lead sulfate (4BS) produced by two different methods (solution and paste) and from two different raw materials (tetragonal PbO and leady oxide) were charaterized by different analytical techniques. The techniques applied were wet-chemical methods, scanning electron microscopy, transmission electron microscopy and X-ray powder diffraction. The preparation method was observed to be the most decisive factor influencing the structure and the morphology of the 4BS pastes in this study.
Effect of the nanotube aspect ratio and surface functionalization on the morphology and properties of multiwalled carbon nanotube polyamide-based fib…
2013
In this study, the effect of the carbon nanotube (CNT) aspect ratio and surface functionalization on the mechanical behavior and morphological changes of polyamide (PA)-based fibers was investigated. Composites were prepared by the melt blending of CNTs with PA, and at a later time, the fibers were prepared by melt spinning and cold drawing. A reinforcement effect was noticed for all of the CNTs samples, and the increase in the mechanical properties and dimensional stability was more pronounced for highly oriented filaments. When the elongational flow was increased, the orientation of CNTs along the fiber direction was observed, but the nanotube alignment was much more difficult for CNTs wi…
Synthesis and characterization of indium oxide at high pressures
2018
Introducción: La naturaleza es sorprendente pero a la vez limitada. A mi entender, nada tiene más potencial que aplicar el ingenio humano para modificar lo que nos rodea y crear algo completamente nuevo. La Física de la Materia Condensada es un campo que actualmente está ganando importancia en la Física moderna. En virtud de los éxitos logrados en Física de la Materia Condensada se han producido enormes avances en el campo de la electrónica cuántica, de los semiconductores y de la ciencia de materiales, teniendo como resultado numerosas aplicaciones tecnológicas que han cambiado nuestras vidas drásticamente en los últimos 50 años. Una de las ramas de la Física de la Materia Condensada es el…