Macromolecular
Crystal Growth

It is widely noted in scientific research that understanding the relevant characteristics and three dimensional structure of a protein enables rational drug design.  The biophysical and structural information of a protein supports the development of specific compounds which can inhibit, regulate or activate the protein which affects the onset or functions of the disease.

Two types of macromolecular crystal growth experiments have been conducted in space in order to: 1) produce more perfect crystals for the determination of biological structures by x-ray or neutron crystallography and 2) understand the process of crystal growth.  The phrase “protein crystal growth” is often used to describe these experiments even though the “proteins” are viruses, DNA, RNA and complexes of these molecules. 

The crystallization of biological macromolecules is an empirical science of

Crystal Growth - Insulin 1g and 0g

rational trial and error.  It requires decreasing the solubility of the macromolecule until it no longer remains in solution and forms an ordered crystal rather than a precipitate.

Microgravity has been posited as an ideal environment for biological crystal growth since buoyancy driven convection and sedimentation are greatly reduced.  As a result, effects that were previously masked can dominate the crystal growth system, e.g. Marangoni convection, and provide unique opportunities to study the crystal growth process.

Microgravity crystal growth experiments can be small and simply operated yet have a high scientific impact.  For this reason, several nations have performed crystal growth experiments in space.  The ability to perform several iterations of crystal growth in microgravity yielded more perfect crystals. 

Experiments that study the process of crystal growth are needed to establish the precise relationship between acceleration levels, depletion zones, crystal growth rates, and crystal diffraction quality.  Such experiments will advance our understanding of crystal growth, a worthwhile aim in itself, but also needed to make the best use of microgravity.

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