Abstract
Dehydration may change the crystal lattice and affect the mosaicity, resolution and quality of X-ray diffraction data. A dehydrating environment can be generated around a crystal in several ways with various degrees of precision and complexity. This study uses a high-precision crystal humidifier/dehumidifier to provide an airstream of known relative humidity in which the crystals are mounted: a precise yet hassle-free approach to altering crystal hydration. A protocol is introduced to assess the impact of crystal dehydration systematically applied to nine experimental crystal systems. In one case, that of glucose isomerase, dehydration triggering a change of space group from I222 to P21212 was observed. This observation is supported by an extended study of the behaviour of the glucose isomerase crystal structure during crystal dehydration.
Highlights
The process of obtaining X-ray diffraction-quality protein crystals can be fraught with difficulties
The average relative humidity of 91% was subsequently used in further experiments to test the validity of relative humidity as a mimic of chemical cryoprotection
Nine crystal systems have been investigated using a generic dehydration protocol to assess the changes induced by crystal dehydration
Summary
The process of obtaining X-ray diffraction-quality protein crystals can be fraught with difficulties. Any crystal obtained will be removed from the mother liquor in which it was grown, exposed to a cryoprotectant and flashcooled in liquid nitrogen (Garman & Schneider, 1997). These challenges navigated, the protein crystal is exposed to X-rays, usually using the intense X-ray beams available at a synchrotron source. This process will result in the collection of useful diffraction data and the protein structure can be solved. In these cases it is not possible to collect a suitable X-ray diffraction data set
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