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Acta crystallographica. Section D, Biological crystallography 08/2011; 67(Pt 8):745. · 12.67 Impact Factor
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ABSTRACT: Recent challenges in biological X-ray crystallography include the processing of modulated diffraction data. A modulated crystal has lost its three-dimensional translational symmetry but retains long-range order that can be restored by refining a periodic modulation function. The presence of a crystal modulation is indicated by an X-ray diffraction pattern with periodic main reflections flanked by off-lattice satellite reflections. While the periodic main reflections can easily be indexed using three reciprocal-lattice vectors a*, b*, c*, the satellite reflections have a non-integral relationship to the main lattice and require a q vector for indexing. While methods for the processing of diffraction intensities from modulated small-molecule crystals are well developed, they have not been applied in protein crystallography. A recipe is presented here for processing incommensurately modulated data from a macromolecular crystal using the Eval program suite. The diffraction data are from an incommensurately modulated crystal of profilin-actin with single-order satellites parallel to b*. The steps taken in this report can be used as a guide for protein crystallographers when encountering crystal modulations. To our knowledge, this is the first report of the processing of data from an incommensurately modulated macromolecular crystal.
Acta crystallographica. Section D, Biological crystallography 07/2011; 67(Pt 7):628-38. · 12.67 Impact Factor
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ABSTRACT: The mosaic structure of a single protein crystal was analyzed by reflection profiling and topography using highly parallel and monochromatic synchrotron radiation. Fine-'-sliced diffraction images (0.002 stills) were collected using a conventional large-area CCD detector in order to calculate reflection profiles. Fine-'-sliced topographic data (0.002) stills were collected with a digital topography system for three reflections in a region where the Lorentz effect was minimized. At room temperature, several different mosaic domains were clearly visible within the crystal. Without altering the crystal orientation, the crystal was cryogenically frozen (cryocooled) and the experiment was repeated for the same three reflections. Topographs at cryogenic temperatures reveal a significantly increased mosaicity, while the original domain structure is maintained. A model for the observed changes during cryocooling is presented.
Appl. Cryst. 01/2006; 39(39):425-432.
