Comparative analysis of space-grown and earth-grown crystals of an aminoacyl-tRNA synthetase: space-grown crystals are more useful for structural determination

Protein crystallization under microgravity aims at benefiting from the quasi-absence of convection and sedimentation to favor well ordered crystal nucleation and growth. The dimeric multidomain enzyme aspartyl-tRNA synthetase from Thermus thermophilus has been crystallized within dialysis reactors of the Advanced Protein Crystallization Facility in the laboratory on earth and under microgravity aboard the US Space Shuttle. A strictly comparative crystallographic analysis reveals that the crystals grown in space are superior in every respect to control crystals prepared in otherwise identical conditions on earth. They diffract X-rays more intensely and have a lower mosaicity, facilitating the process of protein structure determination. Indeed, the electron-density map calculated from diffraction data of space-grown crystals contains considerably more detail. The resulting three-dimensional structure model at 2.0 Å resolution is more accurate than that produced in parallel using the data originating from earth-grown crystals. The major differences between the structures, including the better defined amino-acid side chains and the higher order of bound water molecules, are emphasized.