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EIGER is a single-photon-counting hybrid pixel detector developed at the Paul Scherrer Institut, Switzerland. It is designed for applications at synchrotron light sources with photon energies above 5â keV. Features of EIGER include a small pixel size (75â µm × 75â µm), a high frame rate (up to 23â kHz), a small dead-time between frames (down to 3â µs) and a dynamic range up to 32-bit. In this article, the use of EIGER as a detector for electrons in low-energy electron microscopy (LEEM) and photoemission electron microscopy (PEEM) is reported. It is demonstrated that, with only a minimal modification to the sensitive part of the detector, EIGER is able to detect electrons emitted or reflected by the sample and accelerated to 8-20â keV. The imaging capabilities are shown to be superior to the standard microchannel plate detector for these types of applications. This is due to the much higher signal-to-noise ratio, better homogeneity and improved dynamic range. In addition, the operation of the EIGER detector is not affected by radiation damage from electrons in the present energy range and guarantees more stable performance over time. To benchmark the detector capabilities, LEEM experiments are performed on selected surfaces and the magnetic and electronic properties of individual iron nanoparticles with sizes ranging from 8 to 22â nm are detected using the PEEM endstation at the Surface/Interface Microscopy (SIM) beamline of the Swiss Light Source.
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One of the main challenges in ultrafast material science is to trigger phase transitions with short pulses of light. Here we show how strain waves, launched by electronic and structural precursor phenomena, determine a coherent macroscopic transformation pathway for the semiconducting-to-metal transition in bistable Ti3O5 nanocrystals. Employing femtosecond powder X-ray diffraction, we measure the lattice deformation in the phase transition as a function of time. We monitor the early intra-cell distortion around the light absorbing metal dimer and the long range deformations governed by acoustic waves propagating from the laser-exposed Ti3O5 surface. We developed a simplified elastic model demonstrating that picosecond switching in nanocrystals happens concomitantly with the propagating acoustic wavefront, several decades faster than thermal processes governed by heat diffusion.
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Reliable sample delivery and efficient use of limited beam time have remained bottlenecks for serial crystallography (SX). Using a high-intensity polychromatic X-ray beam in combination with a newly developed charge-integrating JUNGFRAU detector, we have applied the method of fixed-target SX to collect data at a rate of 1â kHz at a synchrotron-radiation facility. According to our data analysis for the given experimental conditions, only about 3 000 diffraction patterns are required for a high-quality diffraction dataset. With indexing rates of up to 25%, recording of such a dataset takes less than 30â s.
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Crystals of a copper-zinc superoxide dismutase from Photobacterium leiognathi, a luminescent marine bacterium that is the species-specific symbiont of the ponyfish, have been obtained from 2-methyl-2,4-pentanediol solutions. The space group was determined using screenless small-angle precession photographs, and was confirmed by analyzing area detector diffraction data with the XENGEN programs for indexing and refinement. The crystals are monoclinic, space group C2 (a = 126.4 A, b = 87.0 A, c = 44.4 A, beta = 92.8 A), and have two 32,000 Mr dimers per asymmetric unit. The crystals diffract to at least 2.7 A resolution, are resistant to radiation damage, and are suitable for determination of the structure by X-ray diffraction.
Assuntos
Photobacterium/enzimologia , Superóxido Dismutase , Difração de Raios XRESUMO
OBJECTIVE: To evaluate the efficacy of intermittent pneumatic compression in treating oedema in the hemiplegic hand of stroke patients. DESIGN: Single-blind randomized control trial. SETTING: acute and rehabilitation elderly care wards in a teaching district. SUBJECTS: 37 Subjects with a first ever hemisphere stroke were randomized to treatment with standard physiotherapy either alone or combined with intermittent pneumatic compression. MAIN OUTCOME MEASURES: The effect of treatment on oedema was assessed using measures of the hand volume of the hemiplegic hand. The impact on function was assessed using the motricity index. RESULTS: The treated group showed no change in the mean stroke hand volume. In the control group the mean stroke hand volume decreased by 3.2 ml. There was no statistically significant difference between the groups. The median scores for the motricity index increased for both groups but there was no significant difference between the groups and any improvement in motor function was independent of any treatment effects. CONCLUSION: Intermittent pneumatic compression at the prescribed pressure and duration of this study is not an effective treatment for the oedematous stroke hand.
Assuntos
Bandagens , Transtornos Cerebrovasculares/complicações , Edema/terapia , Deformidades Adquiridas da Mão/terapia , Idoso , Idoso de 80 Anos ou mais , Edema/etiologia , Feminino , Deformidades Adquiridas da Mão/etiologia , Humanos , Masculino , Método Simples-Cego , Resultado do TratamentoRESUMO
The dimeric high spin c-type cytochrome c' from Chromatium vinosum has been crystallized and the crystals characterized by x-ray diffraction. This cytochrome c' exhibits ligand-controlled dissociation from a dimer to a monomer upon binding carbon monoxide and represents an opportunity to obtain unique information concerning cooperativity in heme proteins. The C. vinosum cytochrome c' protein crystals are grown from polyethylene glycol 4000 and grow in both space group P2(1)2(1)2(1) (a = 49.2, b = 56.7, c = 98.8 A) and space group P2(1) (a = 55, b = 94, c = 50, beta = 106.1 A) depending upon the growth rate, with the P2(1)2(1)2(1) form favored at slower growth rates. The high resolution (2.0 A) atomic structure of the P2(1)2(1)2(1) form is being determined.
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Chromatium/análise , Grupo dos Citocromos c , Monóxido de Carbono/metabolismo , Cristalização , Grupo dos Citocromos c/metabolismo , Substâncias Macromoleculares , Difração de Raios XRESUMO
In principle, protein thermostability depends on efficient interior packing of apolar residues and on avoidance of irreversible denaturation in the unfolded state. To study these effects, the single free cysteine in the highly stable enzyme bovine Cu,Zn superoxide dismutase was mutated to alanine (Cys6----Ala), and the recombinant protein was expressed in yeast, purified, characterized for reversible and irreversible denaturation, crystallized isomorphously to the wild-type enzyme, and used to determine the atomic structure. Removal of the chemically reactive thiol significantly decreased the rate of irreversible denaturation (as monitored by thermal inactivation at 70 degrees C), but the observed energetic cost (delta delta G of 0.7-1.3 kcal/mol as determined by differential scanning calorimetry) was much less than predicted from either the change in hydrophobicity or packing due to removal of the interior sulfur atom. X-ray diffraction data were collected to 2.1-A resolution using an area detector, and the atomic model for the mutant enzyme was determined by fitting to electron density difference maps, followed by reciprocal space refinement both with stereochemical restraints using PROLSQ and with molecular dynamics using X-PLOR. The refined 2.1-A resolution crystallographic structure suggests that small concerted and compensating shifts (less than 0.5 A) of the surrounding side chains and of the adjacent N- and C-terminal beta-strands significantly reduced the energetic cost of the interior mutation by improving packing and stereochemistry in the mutant enzyme. Taken together, these results differentiate between the effects of reversible and irreversible processes as they impact the design of thermostable proteins and suggest that relatively subtle concerted shifts can significantly reduce the energetic cost of evolutionary variation in internal residues of proteins with Greek key beta-barrel folds.
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Cisteína , Superóxido Dismutase/genética , Alanina , Sequência de Aminoácidos , Animais , Varredura Diferencial de Calorimetria , Bovinos , Cristalização , Estabilidade Enzimática , Temperatura Alta , Cinética , Modelos Moleculares , Dados de Sequência Molecular , Mutação , Conformação Proteica , Superóxido Dismutase/metabolismo , Difração de Raios XRESUMO
Eukaryotic Cu,Zn superoxide dismutases (CuZnSODs) are antioxidant enzymes remarkable for their unusually stable beta-barrel fold and dimer assembly, diffusion-limited catalysis, and electrostatic guidance of their free radical substrate. Point mutations of CuZnSOD cause the fatal human neurodegenerative disease amyotrophic lateral sclerosis. We determined and analyzed the first crystallographic structure (to our knowledge) for CuZnSOD from a prokaryote, Photobacterium leiognathi, a luminescent symbiont of Leiognathid fish. This structure, exemplifying prokaryotic CuZnSODs, shares the active-site ligand geometry and the topology of the Greek key beta-barrel common to the eukaryotic CuZnSODs. However, the beta-barrel elements recruited to form the dimer interface, the strategy used to forge the channel for electrostatic recognition of superoxide radical, and the connectivity of the intrasubunit disulfide bond in P. leiognathi CuZnSOD are discrete and strikingly dissimilar from those highly conserved in eukaryotic CuZnSODs. This new CuZnSOD structure broadens our understanding of structural features necessary and sufficient for CuZnSOD activity, highlights a hitherto unrecognized adaptability of the Greek key beta-barrel building block in evolution, and reveals that prokaryotic and eukaryotic enzymes diverged from one primordial CuZnSOD and then converged to distinct dimeric enzymes with electrostatic substrate guidance.
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Photobacterium/enzimologia , Dobramento de Proteína , Estrutura Secundária de Proteína , Superóxido Dismutase/química , Sequência de Aminoácidos , Animais , Sítios de Ligação , Varredura Diferencial de Calorimetria , Bovinos , Clonagem Molecular , Sequência Conservada , Cristalografia por Raios X , Dimerização , Escherichia coli , Peixes/microbiologia , Haemophilus/enzimologia , Humanos , Modelos Moleculares , Dados de Sequência Molecular , Proteínas Recombinantes/biossíntese , Proteínas Recombinantes/química , Proteínas Recombinantes/isolamento & purificação , Homologia de Sequência de Aminoácidos , Superóxido Dismutase/biossíntese , Superóxido Dismutase/isolamento & purificaçãoRESUMO
The active site Cu ion in Cu,Zn superoxide dismutase is alternately oxidized and reduced during the enzymatic dismutation of superoxide to hydrogen peroxide and molecular oxygen. For oxidized Cu,Zn superoxide dismutase, an atomic structure has been determined for the human enzyme at 2.5 A resolution. The resolution of the bovine enzyme structure has been extended to 1.8 A. Atomic resolution data has been collected for reduced and inhibitor-bound Cu,Zn superoxide dismutases, and the interpretation of the electron density difference maps is in progress. The geometry and molecular surfaces of the active sites in these structures, together with biochemical data, suggest a specific model for the enzyme mechanism. Similarities in the active site geometry of the Mn and Fe superoxide dismutases with the Cu,Zn enzyme suggest that dismutation in these enzymes may follow a similar mechanism.