VIRUS AND PROTEIN CRYSTAL-GROWTH ON EARTH AND IN MICROGRAVITY

Protein and virus crystals commonly grown in the laboratory on earth have also been grown in a microgravity environment on the US Space Shuttle. Two techniques for growth of the crystals were investigated: vapour diffusion and direct liquid-liquid diffusion. Crystals produced in microgravity, although generally isomorphous with earth-grown crystals, frequently show positive changes in habit, size and degree of perfection. X-ray diffusion analyses of crystals grown free from gravity usually show an improvement in the intensity-to-background ratio for all resolution ranges, and in some cases an extension of the resolution of the diffraction patterns to a higher limit. Both findings suggest an overall improvement in the quality of macromolecular crystals grown in space. A possible source of this improvement is the formation of depletion zones around crystals growing in microgravity that remain stable in the absence of convection and thereby allow more self-regulated growth. This in turn may be manifested as a more uniform and general ordering of the molecules in the crystal lattice and/or a reduction in gross crystal imperfections. Some illustrative results obtained in two kinds of macromolecular crystal growth experiments on International Microgravity Laboratory-1 are described.