Simulation of some aspects of microgravity in protein crystal growth on Earth

Protein crystallization represents a major success story in the use of the space environment. However, the exact mechanism of the improvement observed in microgravity remains unclear. Several aspects of the space environment have been simulated on earth, and growth monitoring methods developed for space are applied to this simulated environment. The different devices developed can lead to new methods for protein crystal growth and new ways of controlling and improving the growth and final quality of protein crystals. Temperature controlled, free-fall growth of crystals in an upwardly flowing growth solution has been examined. Under these conditions, both the static contact of the crystal with a surface and the sedimentation of the crystals are eliminated. Inhomogeneities in the supply of nutrient are also severely reduced. The effectiveness of this growth method appears dependent upon the type and purity of the protein, and is mainly limited by the consequences of mechanical action on the protein solution. Temperature controlled growth in gels, where gravity induced convection flows are reduced, was monitored with interferometry. Information about the transport of nutrient around the crystal as well as the protein aggregation process were correlated with protein crystal quality. Gel growth has the potential to produce high quality protein crystals, but remains limited in application because of the small amount of data available for the temperature dependence of protein solubility.