MACROMOLECULAR CRYSTAL ANNEALING - OVERCOMING INCREASED MOSAICITY ASSOCIATED WITH CRYOCRYSTALLOGRAPHY

Although cryogenic data collection has become the method of choice for macromolecular crystallography, the flash-cooling step can dramatical ly increase the mosaicity of some crystals. Macromolecular crystal ann ealing significantly reduces the mosaicity of flash-cooled crystals wi thout affecting molecular structure. The process, which cycles a flash -cooled crystal to ambient temperature and back to cryogenic temperatu re, is simple, quick and requires no special equipment. The annealing process has been applied to crystals of several different macromolecul es grown from different precipitants and using a variety of cryoprotec tants. The protocol for macromolecular crystal annealing also has been applied to restore diffraction from flash-cooled crystals that were m ishandled during transfer to or from cryogenic storage. These results will be discussed in relation to crystal mosaicity and effects of radi ation damage in hash-cooled crystals.