A test of macromolecular crystallization in microgravity: large well ordered insulin crystals

Crystals of insulin grown in microgravity on Space Shuttle Mission STS-95 w ere extremely well ordered and unusually large (many >2 mm). The physical c haracteristics of six microgravity and six earth-grown crystals were examin ed by X-ray analysis employing superfine phi slicing and unfocused synchrot ron radiation. This experimental setup allowed hundreds of reflections to b e precisely examined from each crystal in a short period of time. The micro gravity crystals were on average 34 times larger, had sevenfold lower mosai city, had 54-fold higher reflection peak heights and diffracted to signific antly higher resolution than their earth-grown counterparts. A single mosai c domain model could account for the observed reflection profiles in microg ravity crystals, whereas data from earth crystals required a model with mul tiple mosaic domains. This statistically significant and unbiased character ization indicates that the microgravity environment was useful for the impr ovement of crystal growth and the resultant diffraction quality in insulin crystals and may be similarly useful for macromolecular crystals in general .