Protein crystal annealing

  Cryocrystallography has become the method of choice for macromolecular crystallography because of the many advantages conferred by cryogenic data collection. The only significant disadvantage, in some cases, is increased mosaic spread as a result of flash cooling. In crystals containing large unit cells, increased mosaicity can make data reduction difficult to impossible due to reflection overlap. Scientists in the Life Sciences Division Physical Biosciences Division under the direction of Dr. Gerard Bunick have developed a process that, when applied to a flash-cooled crystal, will often lower the mosaic spread. The process has been applied to a number of different macromolecular crystals. Refined values of mosaicity have been observed to improve by greater than a factor of two, and resolution may also improve. Experiments demonstrate that the molecular structure is unaffected by the annealing process. The process has been successfully applied to crystals grown using a number of precipitants, e.g. MPD, (NH4)2SO4 and NaCl. Crystals have been flash cooled using a variety of cryoprotectants and also by using Paratone N to remove surface solution from the crystal. The process is simple, reproducible and promises to routinely improve data quality in flash-cooled crystals of biological macromolecules. It should also extend the application of cryogenic data collection to a wider range of challenging crystals and simplify the handling of flash-cooled crystals.

Contact: Gerry Bunick
Phone: 576-2685
E-mail: bunigk@bio.ornl.gov