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      The minimum crystal size needed for a complete diffraction data set

      a , b , * , b

      Acta Crystallographica Section D: Biological Crystallography

      International Union of Crystallography

      Experimental phasing and radiation damage

      radiation damage, minimum crystal size, protein macromolecular crystallography, scattering power

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          A formula for absolute scattering power is derived to include spot fading arising from radiation damage and the crystal volume needed to collect diffraction data to a given resolution is calculated.


          In this work, classic intensity formulae were united with an empirical spot-fading model in order to calculate the diameter of a spherical crystal that will scatter the required number of photons per spot at a desired resolution over the radiation-damage-limited lifetime. The influences of molecular weight, solvent content, Wilson B factor, X-ray wavelength and attenuation on scattering power and dose were all included. Taking the net photon count in a spot as the only source of noise, a complete data set with a signal-to-noise ratio of 2 at 2 Å resolution was predicted to be attainable from a perfect lysozyme crystal sphere 1.2 µm in diameter and two different models of photoelectron escape reduced this to 0.5 or 0.34 µm. These represent 15-fold to 700-fold less scattering power than the smallest experimentally determined crystal size to date, but the gap was shown to be consistent with the background scattering level of the relevant experiment. These results suggest that reduction of background photons and diffraction spot size on the detector are the principal paths to improving crystallographic data quality beyond current limits.

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          Author and article information

          Acta Crystallogr D Biol Crystallogr
          Acta Cryst. D
          Acta Crystallographica Section D: Biological Crystallography
          International Union of Crystallography
          01 April 2010
          24 March 2010
          24 March 2010
          : 66
          : Pt 4 ( publisher-idID: d100400 )
          : 393-408
          [a ]Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158-2330, USA
          [b ]Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
          Author notes
          Correspondence e-mail: jmholton@
          ba5148 ABCRE6 S0907444910007262
          © Holton & Frankel 2010

          This is an open-access article distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.

          Experimental phasing and radiation damage
          Research Papers


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