Keiko Miura

Japan Synchrotron Radiation Research Institute (JASRI), Tatsuno, Hyōgo, Japan

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Publications (7)11.29 Total impact

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    ABSTRACT: The arm light organ of the firefly squid, Watasenia scintillans, emits extremely bright flashes of light, which are caused by a luciferin-luciferase reaction involving ATP, Mg(2+) and molecular oxygen. The molecular mechanism underlying the bioluminescence reaction has remained unresolved, because the luciferase could not be identified or isolated. The arm light organ contains numerous rod-like bodies that are 2-6 μm long and 1-2 μm thick. This paper addresses the characterization of the extracted rod-like body. We found that the rod-like bodies emit the light in vitro by the luciferin-luciferase reaction. Furthermore, by using the X-ray powder diffraction method, we confirmed that the rod-like bodies are well-ordered microcrystals.
    FEBS letters 08/2011; 585(17):2735-8. · 3.54 Impact Factor
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    ABSTRACT: X-ray diffraction patterns from a film of oriented purple membranes, which comprise two-dimensional crystals of bacteriorhodopsin (BR) trimers, were recorded with a 1 m-pathlength Guinier-type camera at SPring-8 BL40B2. A well focused X-ray beam and a camera with a high angular resolution of 0.024 degrees enabled a powder diffraction profile with very sharp and well separated peaks to be obtained up to a resolution of 2.3 A. Using integrated diffraction intensities up to a Bragg spacing of 4.2 A, a cluster of bulky amino acid residues and the head group of the BR chromophore are apparent in the electron density map projected along the membrane normal. Thus, a combination of synchrotron X-rays and large Guinier camera can be used for analyzing the conformational changes of BR in the intact state. In addition, the method might be extended to the structural analysis of film materials composed of two-dimensional arrays of nanoparticles.
    Journal of Synchrotron Radiation 06/2006; 13(Pt 3):281-4. · 2.19 Impact Factor
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    ABSTRACT: Hierarchical features of the thermal unfolding-refolding structural transition of hen egg white lysozyme (HEWL) have been studied in the temperature range from 13 to 84 degrees C by using high-resolution wide-angle X-ray scattering (WAXS) measurements at a third-generation synchrotron source. We have gathered high-statistic WAXS data of the reversible unfolding-refolding process of HEWL in the q range from approximately 0.05 to approximately 3 A(-1) [q = (4pi/lambda) sin(theta/2), where theta is the scattering angle and lambda the wavelength]. This measured q range corresponds to the spatial distance from approximately 2 to approximately 125 A, which covers all hierarchical structures of a small globular protein such as HEWL, namely, tertiary, domain, and secondary structures. Because of this, we have found that the pH dependence of the thermal structural transition of HEWL is well characterized by the various hierarchical levels and the transition concurrence among them. In this report, we present a new hierarchical map depiction of unfolding-refolding transitions. Using scattering with various ranges of q values, we determine the molar ratio of native-like protein structure defined by the data in each range, thus producing a map of the amount of native-like structure as a function of the hierarchical level or resolution. This map can visualize a detailed feature of the unfolding-refolding transition of a protein depending on various structural hierarchical levels; however, the exact meaning of the map will await sharpening by additional works.
    Biochemistry 08/2004; 43(28):9036-49. · 3.38 Impact Factor
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    ABSTRACT: The SPring‐8 bending magnet beamline BL38B1 is designed for R&D of optics, detectors, experiments for XAFS and protein X‐ray crystallography (PX). This beamline has a multi‐purpose hutch for two experimental stations of XAFS and PX, and removable optical benches used for R&D of detectors and instruments. The design and the performance of the beamline are presented. © 2004 American Institute of Physics
    AIP Conference Proceedings. 05/2004; 705(1):486-489.
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    ABSTRACT: BL40B2 and BL40XU were built at SPring‐8 in 1999. They are now open for public users and many kinds of small angle x‐ray scattering experiments are carried out using these beamlines. We report the present status of these two beamlines. Also some examples of experimental results that were obtained at these beamlines are shown. BL40B2 is for recording small‐angle x‐ray scattering from non‐crystalline biological materials. The light source is a bending magnet and the white x‐rays generated by are monochromatized using a double crystal monochromator and focused by a 1‐m‐long rhodium‐coated bent‐cylinder mirror. The photon flux is 1×1011 photons/sec at 12.4 keV. The tunable energy range is 7 keV ∼ 18 keV. As a detector, an imaging plate area detector (RIGAKU R‐AXIS IV++) is installed. Two fixed‐length vacuum paths allow camera lengths of 400 mm and 1000 mm. This beamline is suitable for static measurements with high accuracy and high resolution. The aim of BL40XU is to provide very high flux of x‐rays for various experiments. On this concept, BL40XU was designed to use the fundamental undulator radiation as a quasi‐monochromatic x‐ray beam so that the use of the crystal monochromator was eliminated. The x‐ray source of BL40XU is a helical undulator and its flux is estimated to be 1×10∧15 photons/sec at 12.4 keV. The x‐ray is focused horizontally and vertically by bending two water‐cooled focusing mirrors. So far, various time‐resolved diffraction and scattering experiments on biomaterials and polymers have been carried out. © 2004 American Institute of Physics
    AIP Conference Proceedings. 05/2004; 705(1):336-339.
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    ABSTRACT: In the present study using a high-intensity X-ray beam from a third-generation synchrotron radiation source, it is demonstrated that a wide-angle X-ray scattering (WAXS) profile from several globular proteins in solution can reflect not only the overall structures (approximately 300 A distance resolution) but also intramolecular structures ranging to secondary structures (approximately 2.5 A distance resolution). The proteins treated in the present experiments are classified as different types of structure categories, namely, as all-alpha, all-beta and alpha + beta proteins. Here the full-range experimental scattering curves are compared with the theoretical curves, suggesting a further availability of the SR-WAXS method for studies of structure hierarchy and the function of proteins in solutions.
    Journal of Synchrotron Radiation 08/2002; 9(Pt 4):202-5. · 2.19 Impact Factor
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    ABSTRACT: A powder diffractometer of Guinier geometry was developed and tested on a beamline, BL40B2, at SPring-8. The long specimen-to-detector distance, 1,000 mm, is advantageous in recording diffraction from Bragg spacing of 20 nm or larger. The angular resolution, 0.012 degrees, was realized together with the focusing optics, the long specimen-to-detector distance and the small pixel size of Blue-type Imaging Plate detector. Such a high resolution makes the peak separation possible in the powder diffraction from microcrystals with large unit cell and low symmetry of biological macromolecules.