Tracking reflections through cryogenic cooling with topography

The mosaic structure of a single protein crystal was analyzed by reflection profiling and topography using highly parallel and monochromatic synchrotron radiation. Fine-φ-sliced diffraction images (0.002° stills) were collected using a conventional large-area CCD detector in order to calculate reflection profiles. Fine-φ-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.