Lessons from crystals grown in the Advanced Protein Crystallisation Facility for conventional crystallisation applied to structural biology.

The crystallog. quality of protein crystals that were grown in microgravity has been compared to that of crystals that were grown in parallel on earth gravity under otherwise identical conditions. A goal of this comparison was to assess if a more accurate 3D-structure can be derived from crystallog. anal. of the former crystals. Therefore, the properties of crystals prepd. with the Advanced Protein Crystn. Facility (APCF) on earth and in orbit during the last decade were evaluated. A statistical anal. reveals that about half of the crystals produced under microgravity had a superior x-ray diffraction limit with respect of terrestrial controls. Eleven protein structures could be detd. at previously unachieved resolns. using crystals obtained in the APCF. Microgravity induced features of the most relevant structures are reported. A second goal of this study was to identify the cause of the crystal quality enhancement useful for structure detn. No correlations between the effect of microgravity and other system-dependent parameters, such as isoelec. point or crystal solvent content, were found except the reduced convection during the crystn. process. Thus, crystal growth under diffusive regime appears to be the key parameter explaining the beneficial effect of microgravity on crystal quality. The mimicry of these effects on earth in gels or in capillary tubes is discussed and the practical consequences for structural biol. highlighted.