X-RAY TOPOGRAPHIC STUDIES OF PROTEIN CRYSTAL PERFECTION AND GROWTH

The effects of solution variations during growth on the perfection of tetragonal lysozyme crystals have been characterized using X-ray topog raphy and high angular and wavevector resolution reciprocal-space scan s. X-ray images of crystals grown under nearly uniform conditions show little contrast or evidence of defects. and mosaic widths of these cr ystals are comparable with those reported for microgravity-grown cryst als. Images of crystals for which solution conditions (temperature, pi i or salt concentration) are changed after an initial period of unifor m growth can show extensive contrast, indicating the presence of disor der. The X-ray mosaic widths of these crystals can be significantly br oadened, but their radial widths are at mast Fiery slightly broadened, indicating that image contrast is primarily due to mosaicity. Compari son of X-ray images with mosaic scans indicates that regions grown aft er the change in solution conditions have broader mosaicities and are more disordered; that regions grown immediately after the change tend to have broader mosaicities than subsequent growth regions, and that t he prechange growth region is largely unaffected by-solution changes. The observed disorder may arise from solution change-related transient growth instabilities, from transient liquid-liquid phase separation t hat can occur during the change, and from post-change relaxation of th e lattice constant of the pre-change growth regions. These results sug gest that solution variations during growth, including those typical o f macroseeding, vapor-diffusion growth and other widely used technique s, map be an important source of disorder in some protein crystals.