Search results for "electron microscopy"
showing 10 items of 706 documents
Evolution of molluscan hemocyanin structures
2013
AbstractHemocyanin transports oxygen in the hemolymph of many molluscs and arthropods and is therefore a central physiological factor in these animals. Molluscan hemocyanin molecules are oligomers composed of many protein subunits that in turn encompass subsets of distinct functional units. The structure and evolution of molluscan hemocyanin have been studied for decades, but it required the recent progress in DNA sequencing, X-ray crystallography and 3D electron microscopy to produce a detailed view of their structure and evolution. The basic quaternary structure is a cylindrical decamer 35nm in diameter, consisting of wall and collar (typically at one end of the cylinder). Depending on th…
Finely Tuned Temperature-Controlled Cargo Release Using Paraffin-Capped Mesoporous Silica Nanoparticles
2011
[EN] Trapped: Mesoporous silica nanoparticles were loaded with a fluorescent guest and functionalized with octadecyltrimethoxysilane. The alkyl chains interact with paraffins, which build a hydrophobic layer around the particle (see picture). Upon melting of the paraffin, the guest molecule is released, as demonstrated in cells for the guest doxorubicin. The release temperature can be tuned by choosing an appropriate paraffin. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Limulus polyphemus Hemocyanin: 10 Å Cryo-EM Structure, Sequence Analysis, Molecular Modelling and Rigid-body Fitting Reveal the Interfaces Between th…
2007
Abstract The blue copper protein hemocyanin from the horseshoe crab Limulus polyphemus is among the largest respiratory proteins found in nature (3.5 MDa) and exhibits a highly cooperative oxygen binding. Its 48 subunits are arranged as eight hexamers (1×6mers) that form the native 8×6mer in a nested hierarchy of 2×6mers and 4×6mers. This quaternary structure is established by eight subunit types (termed I, IIA, II, IIIA, IIIB, IV, V, and VI), of which only type II has been sequenced. Crystal structures of the 1×6mer are available, but for the 8×6mer only a 40 A 3D reconstruction exists. Consequently, the structural parameters of the 8×6mer are not firmly established, and the molecular inte…
Nautilus pompilius Hemocyanin: 9 Å Cryo-EM Structure and Molecular Model Reveal the Subunit Pathway and the Interfaces between the 70 Functional Units
2007
Hemocyanins are giant extracellular oxygen carriers in the hemolymph of many molluscs. Nautilus pompilius (Cephalopoda) hemocyanin is a cylindrical decamer of a 350 kDa polypeptide subunit that in turn is a "pearl-chain" of seven different functional units (FU-a to FU-g). Each globular FU has a binuclear copper centre that reversibly binds one O(2) molecule, and the 70-FU decamer is a highly allosteric protein. Its primary structure and an 11 A cryo-electron microscopy (cryo-EM) structure have recently been determined, and the crystal structures of two related FU types are available in the databanks. However, in molluscan hemocyanin, the precise subunit pathway within the decamer, the inter…
Keyhole limpet hemocyanin: 9-A CryoEM structure and molecular model of the KLH1 didecamer reveal the interfaces and intricate topology of the 160 fun…
2008
Abstract Hemocyanins are blue copper-containing respiratory proteins in the hemolymph of many arthropods and molluscs. Molluscan hemocyanins are decamers, didecamers, or multidecamers of a 340- to 400-kDa polypeptide subunit containing seven or eight globular functional units (FUs; FU-a to FU-h), each with an oxygen-binding site. The decamers are short 35-nm hollow cylinders, with their lumen narrowed by a collar complex. Our recently published 9-A cryo-electron microscopy/crystal structure hybrid model of a 3.4-MDa cephalopod hemocyanin decamer [Nautilus pompilius hemocyanin (NpH)] revealed the pathway of the seven-FU subunit (340 kDa), 15 types of inter-FU interface, and an asymmetric col…
10-A cryoEM structure and molecular model of the Myriapod (Scutigera) 6x6mer hemocyanin:understanding a giant oxygen transport protein
2009
Oxygen transport in Myriapoda is maintained by a unique 6x6mer hemocyanin, that is, 36 subunits arranged as six hexamers (1x6mers). In the sluggish diplopod Spirostreptus, the 1x6mers seem to operate as almost or fully independent allosteric units (h approximately 1.3; P(50) approximately 5 torr), whereas in the swift centipede Scutigera, they intensively cooperate allosterically (h approximately 10; P(50) approximately 50 torr). Here, we show the chemomechanical basis of this differential behavior as deduced from hybrid 6x6mer structures, obtained by single-particle cryo-electron microscopy of the Scutigera 6x6mer (10.0 A resolution according to the 0.5 criterion) and docking of homology-m…
Comparison of the decameric structure of peroxiredoxin-II by transmission electron microscopy and X-ray crystallography
2001
Abstract The decameric human erythrocyte protein torin is identical to the thiol-specific antioxidant protein-II (TSA-II), also termed peroxiredoxin-II (Prx-II). Single particle analysis from electron micrographs of Prx-II molecules homogeneously orientated across holes in the presence of a thin film of ammonium molybdate and trehalose has facilitated the production of a ≥20 A 3-D reconstruction by angular reconstitution that emphasises the D5 symmetry of the ring-like decamer. The X-ray structure for Prx-II was fitted into the transmission electron microscopic reconstruction by molecular replacement. The surface-rendered transmission electron microscopy (TEM) reconstruction correlates well…
Structural Mechanism of SDS-Induced Enzyme Activity of Scorpion Hemocyanin Revealed by Electron Cryomicroscopy
2009
Summary Phenoloxidases (POs) occur in all organisms and are involved in skin and hair coloring in mammals, and initiating melanization in wound healing. Mutation or overexpression of PO can cause albinism or melanoma, respectively. SDS can convert inactive PO and the oxygen carrier hemocyanin (Hc) into enzymatically active PO. Here we present single-particle cryo-EM maps at subnanometer resolution and pseudoatomic models of the 24-oligomeric Hc from scorpion Pandinus imperator in resting and SDS-activated states. Our structural analyses led to a plausible mechanism of Hc enzyme PO activation: upon SDS activation, the intrinsically flexible Hc domain I twists away from domains II and III in …
Quaternary structure of the European spiny lobster (Palinurus elephas) 1x6-mer hemocyanin from cryoEM and amino acid sequence data.
2002
Abstract Arthropod hemocyanins are large respiratory proteins that are composed of up to 48 subunits (8×6-mer) in the 75 kDa range. A 3D reconstruction of the 1×6-mer hemocyanin from the European spiny lobster Palinurus elephas has been performed from 9970 single particles using cryoelectron microscopy. An 8 A resolution of the hemocyanin 3D reconstruction has been obtained from about 600 final class averages. Visualisation of structural elements such as α-helices has been achieved. An amino acid sequence alignment shows the high sequence identity (>80%) of the hemocyanin subunits from the European spiny lobster P. elephas and the American spiny lobster Panulirus interruptus . Comparison of…
Bacteriophage P23-77 capsid protein structures reveal the archetype of an ancient branch from a major virus lineage.
2013
Summary It has proved difficult to classify viruses unless they are closely related since their rapid evolution hinders detection of remote evolutionary relationships in their genetic sequences. However, structure varies more slowly than sequence, allowing deeper evolutionary relationships to be detected. Bacteriophage P23-77 is an example of a newly identified viral lineage, with members inhabiting extreme environments. We have solved multiple crystal structures of the major capsid proteins VP16 and VP17 of bacteriophage P23-77. They fit the 14 Å resolution cryo-electron microscopy reconstruction of the entire virus exquisitely well, allowing us to propose a model for both the capsid archi…