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  • 1
    Electronic Resource
    Electronic Resource
    A Minimalist's Approach to the Phase Problem – Phasing Selenomethionyl Protein Structures Using Cu Kα Data (1996)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 52 (1996), S. 1075-1081 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The feasibility of phasing protein structures through the use of the isomorphous and anomalous signal of selenomethionyl (Se-Met) derivative and diffraction data collected with a standard laboratory Cu Kα X-ray source has been investigated. Interpretable electron-density maps were obtained for the core domain of avian sarcoma virus integrase, a typical medium-sized protein having four Met residues in a sequence of 156 amino acids. The r.m.s. difference between 3.1 Å experimental phases obtained from Se-Met Cu Kα data and the final phases calculated from the refined model is 55°. A procedure combining single isomorphous replacement/single anomalous scattering phasing and solvent flattening for data based on a single Se-Met derivative and Cu Kα radiation has been tested on this and another protein. The results are encouraging enough to indicate that such procedures might be recommended when a synchrotron source is not readily available.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444996008402
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  • 2
    Electronic Resource
    Electronic Resource
    Structure of Monellin Refined to 2.3 Å Resolution in the Orthorhombic Crystal Form (1997)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 53 (1997), S. 713-719 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The structure of orthorhombic crystals of monellin, a sweet protein extracted from African serendipity berries, has been solved by molecular replacement and refined to 2.3 Å resolution. The final R factor was 0.150 for a model with excellent geometry. A monellin molecule consists of two peptides that are non-covalently bound, with chain A composed of three β-strands interconnected by loop regions and chain B composed of two β-strands interconnected by an α-helix. The N terminus of chain A is in close proximity to the C terminus of chain B. The two molecules in the asymmetric unit are related by a non-crystallographic twofold axis and form a dimer, similar to those previously observed in other crystal forms of both natural and single-chain monellin. The r.m.s, deviation between the Cα atoms in the two independent molecules is 0.60 Å, while the deviations from the individual molecules in the previously reported monoclinic crystals are 0.50–0.57 Å. This result proves that the structure of monellin is not significantly influenced by crystal packing forces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444997006860
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  • 3
    Electronic Resource
    Electronic Resource
    Absorption correction for Weissenberg diffractometers (1980)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 442-450 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Formulas are derived extending several semi-empirical absorption-correction methods to diffractometers operating in Weissenberg geometries, with particular attention paid to flat-cone geometry. These formulas are useful for a variety of instruments using both area and linear position-sensitive detectors. While a complete data set can sometimes be corrected using a single absorption reflection, it was found that the best corrections are usually obtained by considering two absorption reflections rather than one. A discussion of the optimum choice of absorption correction when a crystal has at least a twofold symmetry axis is presented. The accuracy of the methods and the limits of applicability have been examined by computer simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739480000952
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  • 4
    Electronic Resource
    Electronic Resource
    Improved technique for peak integration for crystallographic data collected with position-sensitive detectors: a dynamic mask procedure (1981)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 594-604 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A technique for improving the precision of crystal data collected on films or with electronic position-sensitive detectors is proposed. The extent of each medium or strong reflection is computed independently, after smoothing and filtering the individual intensities, producing a variable 'dynamic mask'. A method of calculating universal background profiles, which preserves the data and limits the necessary storage, is introduced. The method was applied to data collected with X-ray precession and oscillation techniques and to neutron data collected with a fiat-cone diffractometer equipped with a linear detector. In all cases substantial improvement in the precision of weaker reflections was observed. The overall quality of the data was particularly enhanced in the neutron diffraction case.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739481001332
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  • 5
    Electronic Resource
    Electronic Resource
    A procedure for joint refinement of macromolecular structures with X-ray and neutron diffraction data from single crystals (1982)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 38 (1982), S. 239-247 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A procedure is presented for the stereochemically restrained least-squares refinement of macromolecular structures with neutron and X-ray diffraction data from single crystals. This procedure has been tested by refining a model of ribonuclease A using neutron data to minimal spacings of 2.8 Å and X-ray data from within 2.0 Å spacings. Joint X-ray and neutron refinement is well conditioned and tends to avoid false minima that may occur when a medium-resolution structure is refined solely with the neutron structure factors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739482000527
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  • 6
    Electronic Resource
    Electronic Resource
    Refined crystal structure of Acinetobacter glutaminasificans glutaminase–asparaginase (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 826-832 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The crystal structure of glutaminase–asparaginase from Acinetobacter glutaminasificans has been reinterpreted and refined to an R factor of 0.171 at 2.9 Å resolution, using the same X-ray diffraction data that were used to build a preliminary model of this enzyme [Ammon, Weber, Wlodawer, Harrison, Gilliland, Murphy, Sjölin & Roberts (1988). J. Biol. Chem. 263, 150–156]. The current model, which does not include solvent, is based in part on the related structure of Escherichia coli asparaginase and is significantly different from the structure of the enzyme from A. glutaminasificans described previously. The reason for the discrepancies has been traced to insufficient phasing power of the original heavy-atom derivative data, which could not be compensated for fully by electron-density modification techniques. The corrected structure of A. glutaminasificans glutaminase–asparaginase is presented and compared with the preliminary model and with the structure of E. coli asparaginase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444994003446
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  • 7
    Electronic Resource
    Electronic Resource
    Analysis of solvent structure and hydrogen exchange in proteins on the basis of neutron diffraction data from deuterated and hydrogenous crystals (1988)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 44 (1988), S. 309-320 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A method has been developed to determine the structure of bound solvent and the positions of exchanged hydrogens in proteins, on the basis of neutron diffraction from hydrogenous and deuterated crystals. In this method phases for the hydrogenous and for the deuterated model are refined simultaneously, and an average model is imposed in the volume occupied by non-hydrogen atoms. The densities in the areas of bulk solvent are replaced by their average values, while no modifications are performed in the vicinity of ordered solvents and potentially exchangeable hydrogens. The method was tested on 1.8 Å neutron diffraction data collected from two crystals of bovine pancreatic trypsin inhibitor, one of them deuterated and the other hydrogenous. Significant improvement was observed for the densities corresponding to many partially occupied solvent sites, as well as to partially exchanged hydrogens. The algorithm presented here has been compared with a different approach published recently by Shpungin & Kossiakoff [Methods Enzymol. (1986), 127, 329-342].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S010876738701242X
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  • 8
    Electronic Resource
    Electronic Resource
    Applications of synchrotron radiation to protein crystallography. II. Anomalous scattering, absolute intensity and polarization (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 445-455 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The synchrotron X-ray beam produced by the SPEAR storage ring at the Stanford Linear Accelerator Center has been used as a tuneable and intense source for single-crystal-protein diffraction experiments. A measurement of the absolute intensity of a focused, monochromatized X-ray beam gave a value of 3 × 109 photons s-1 at a wavelength of 1.74 Å for typical machine operating conditions. A series of hk0 precession photographs were obtained from a crystal of the Fe-containing protein rubredoxin to investigate anomalous scattering effects and study their use in phase determination. Seven discrete wavelengths of radiation were used, some above and some below the Fe K absorption edge (1.743 Å = 7.111 keV). The rubredoxin diffraction data showed intensity changes due to f' varying with wavelength as well as from Bijvoet differences. The Fe site could be correctly located from difference Patterson and Fourier maps based either on f' or f”. The signal to noise ratio at the iron site was enhanced by calculating combined f' and f” maps. The phases of the Bragg reflections were also obtained from three films collected at different wavelengths. When compared with the known phases for rubredoxin, the differences average to 60°, which indicates that some phasing information was available even from the relatively poor data and that this method will be potentially useful in future applications. A method for calculating the Lp factor which has to be applied to precession photographs taken with the polarized synchrotron X-ray beam is described in the Appendix.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739477001168
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  • 9
    Electronic Resource
    Electronic Resource
    Diffraction and NMR studies of proteins: an uneasy alliance
    Amsterdam : Elsevier
    Trends in Biochemical Sciences 7 (1982), S. 389-391 
    Details
    ISSN: 0968-0004
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0968-0004(82)90179-7
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  • 10
    Electronic Resource
    Electronic Resource
    Ultracentrifugation at moderate pressures
    Amsterdam : Elsevier
    Analytical Biochemistry 34 (1970), S. 359-365 
    Details
    ISSN: 0003-2697
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0003-2697(70)90120-X
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