RESULTS
The PCG-EGN experiment was a platform that provided an economical and potential high-
volume avenue to produce biological protein crystals in microgravity. The samples used in the
EGN Dewar were placed into individual tubes, flash
frozen, and allowed to warm to the ambient
temperature aboard the ISS. Crystals produced in
microgravity when compared to their counterparts
grown on Earth are usually larger and more
defined in structure making them better
candidates for X-ray diffraction studies. The X-ray
diffraction studies show researchers the structure
of the molecules in the proteins, and once the
structure is understood, the active sites can be
determined, which may lead to improvement in
medical treatment for certain conditions.
Successful crystallization rates were as follows:
Expedition 0 (prior to permanent human
occupation of ISS), 10 of 24 proteins and viruses; Expedition 1, 4 of 23 proteins and viruses;
Expedition 2, 6 of 8 proteins and both viruses; Expedition 4, 3 of 9 proteins and 0 of 2 viruses.
Major crystals obtained included Bence-Jones protein, Bromegrass Mosaic Virus, canavalin,
lysozyme, pea lectin, thaumatin, trypsin, and 4a-hydroxy-tetrahydropterin dehydratase (DcoH).
Overall the rate of successful crystallizations was not as high as expected. Although many of the
crystals produced were no better than those obtained in the ground laboratory, there were still
some significant structural results. When compared to their Earth-grown counterparts, the
space-grown thaumatin crystals diffracted to a higher resolution, and some crystals showed as
much as 40% more intensity during the diffraction process. This resulted in a more accurate
protein structure model (electron density map) being produced from the space-grown crystal
data. The pea lectin crystals also diffracted to higher resolution than their Earth-grown
counterparts. Data from the space-grown crystals were the best obtained, giving rise to the
highest resolution structure for pea lectin. A refinement for the structural model of pea lectin is
in progress. DcoH crystals grown on Expedition 1 also appeared to be of better quality than
those grown on Earth.
Student investigations across the 4 Expeditions were successful in crystallizing a number of
proteins. Although many of the crystals did not appear to be better than previously analyzed
crystals, some of the crystals from Expedition 2 were used for microscopic observation and X-
ray examination.
PUBLICATION(S)
Barnes CL, Snell EH, Kundrot CE. Thaumatin crystallization aboard the International Space
Station using liquid-liquid diffusion in the Enhanced Gaseous Nitrogen Dewar (EGN). Acta
Crystallographica Section D: Biological Crystallography. 2002;58(Pt 5):751-760.
Catalase crystals grown in microgravity during
International Space Station Expedition 4.
NASA Marshall Space Center image.