Journal
ACTA CRYSTALLOGRAPHICA SECTION D-STRUCTURAL BIOLOGY
Volume 61, Issue -, Pages 891-898Publisher
INT UNION CRYSTALLOGRAPHY
DOI: 10.1107/S0907444905008541
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Funding
- NIGMS NIH HHS [R01 GM061909, GM61909] Funding Source: Medline
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Nucleosome core-particle crystals are routinely flash-cooled in liquid propane at temperatures of similar to 153 K, followed by transfer into a cold nitrogen-gas stream (similar to 93 K). Analysis of diffraction data from crystals flash-cooled at different temperatures shows that the optimal temperature is similar to 153 K. The data quality worsens, with a concomitant reduction in the diffraction limit, at temperatures both higher and lower than 153 K. With some batches of crystals, significant shrinkage of the unit-cell volume is also observed at temperatures of 138 K and lower. The lattice shrinkage is always restricted to the c axis, concurrent with closer packing of two nucleosomes. Direct plunge-cooling of crystals in liquid nitrogen leads to loss of diffraction quality and resolution limit. Thus, in cases where flash-cooling into liquid nitrogen is detrimental to diffraction, optimizing cooling protocols at higher temperatures using liquid propane or other cryogens with similar properties may lead to dramatically improved results. In a related study, it is shown that a nucleosome crystal transported under 'cryocooled' conditions has higher mosaicity and yields inferior data quality in comparison to a crystal cryocooled at the synchrotron. For fragile crystals, transport in mother liquor and/or cryoprotectant followed by subsequent flashcooling at the synchrotron may be the best procedure.
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