Improvements in lysozyme protein crystal perfection through microgravity growth.

Microgravity offers an environment for protein crystallization where there is an absence of convection and sedimentation. We have investigated the effect of microgravity conditions on the perfection of protein crystals. The quality of crystals for X-ray diffraction studies is characterized by a number of factors, namely size, mosaicity and the resolution 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-grown ground control values. These microgravity-grown protein crystals are 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 offers a particularly important opportunity for improving the measurement of 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.