NIST COLLABORATION USES MICROGRAVITY TO IMPROVE PROTEIN CRYSTAL GROWTH.

NIST scientists are collaborating with a private company in the growth of ribonuclease crystals in space. X-ray diffraction topography, which has only recently been applied to protein crystals, was used to probe the differences between crystals grown on the space shuttle and crystals grown at the same time on the earth. The topographs from the space-grown crystals showed that they were of higher crystalline perfection than the ground grown crystals. The images of the space-grown crystals were more uniform and sharply defined. The symmetry was consistent with nucleation followed by homogeneous symmetric growth. This growth mechanism is possible in microgravity but not likely on earth where there is sedimentation and convection-induced asymmetry. On the other hand, the earth-grown crystals had a less well-defined microstructure with no clearly identifiable features and there was no consistent symmetry of the images. All of these features indicate lower quality crystals with a higher-defect density. In addit ion to quality improvements, microgravity also improves crystal harvesting. Approximately 80 % of the crystals grown in microgravity were free-floating in the growth chamber, facilitating removal. In contrast, approximately 80 % of the earth-grown crystals grew attached to the growth chamber making harvesting more difficult. These results clearly demonstrate the advantages of a microgravity environment for growing protein crystals.