IMPROVEMENTS IN LYSOZYME PROTEIN CRYSTAL PERFECTION THROUGH MICROGRAVITY GROWTH

Microgravity offers an environment for protein crystallization where t here is an absence of convection and sedimentation. We have investigat ed the effect of microgravity conditions on the perfection of protein crystals. The quality of crystals for X-ray diffraction studies is cha racterized by a number of factors, namely size, mosaicity and the reso lution limit. By using tetragonal lysozyme crystals as a test case we show, with crystal growth in two separate Space Shuttle missions, that the mosaicity is improved by a factor of three to four over earth-gro wn ground control values. These microgravity-grown protein crystals ar e then essentially perfect diffraction gratings. As a result the peak to background of individual X-ray diffraction reflections is enhanced by a similar factor to the reduction in the mosaicity. This then offer s a particularly important opportunity for improving the measurement o f weak reflections such as occur at high diffraction resolution. These microgravity results set a benchmark for all future microgravity and earth-based protein crystallography procedures.