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  • 1
    Electronic Resource
    Electronic Resource
    Positioning a protein molecule in the asymmetric unit using very low order reflections and packing restraints (1999)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 32 (1999), S. 530-535 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method for predicting the position of protein molecules in the unit cell is presented. This prediction is based on the structure-factor amplitudes of the very low order reflections and packing considerations. With very low resolution data, the calculated electron density is very blurred, such that a protein molecule may well be approximated as a sphere. A sphere with the same volume as the unknown protein was translated in small (2–3 Å) steps in the corresponding Cheshire cell until maximum overlap between the amplitudes calculated from the sphere and the true protein structure was found. A molecular packing can be calculated to restrain the allowable regions. This makes the positioning of the protein molecule even more reliable. Structure factors of the ten or so lowest resolution reflections were calculated with a sphere at the best position. These structure factors agreed closely with those of the true protein structure. The translation algorithm has been successfully tested for 16 proteins. For 12 out of 16 proteins tested, the position of the centre of the molecule was correctly predicted to within 5 Å. A qualitative deduction of deviations from the spherical model can be gained by comparing structure factors from the spherical model and the true protein. The very low resolution phasing obtained by this method may be used as powerful starting set for phase-extension methods such as maximum entropy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889899003209
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  • 2
    Electronic Resource
    Electronic Resource
    The protein content in crystals and packing coefficients in different space groups (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 789-790 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A precise way of estimating the packing coefficient, i.e. the ratio between the protein and unit-cell volume, or solvent content in protein crystals is given. At present, the solvent content is not given for most proteins in the Protein Data Bank and in many cases where it is given the values are dubious. The mean density of proteins in the crystalline form is around 1.22 g cm−3, not 1.35 g cm−3 as usually stated. This is equivalent to 19.5 Å3 per non-H atom. A statistical investigation of the average protein content and packing coefficient in different space groups is presented. The packing coefficients are generally higher in the most frequently occurring space groups than in the uncommon space groups. There is also a remarkable difference in frequency distribution for enantiomorphous pairs of space groups.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444900005163
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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