Improving the X-ray resolution by reversible flash-cooling combined with concentration screening, as exemplified with PPase

A significant improvement in the X-ray resolution of crystals of Escherichia coli inorganic pyrophosphatase at cryo-temperature was obtained as a result of studying the relationship between the crystal order and cryosolution component concentrations. To perform the experiments, the ability to reverse the flash-cooling process and to return a crystal to ambient temperature was used. In each cycle, the crystal was transferred from a cold nitrogen-gas stream to a cryosolution with modified concentrations of the components. The crystal was then flash-cooled again and the diffraction quality checked. Such a technique allows the screening of a wide concentration range rather quickly without using a large number of crystals and allows the determination of optimal cryosolution component concentrations. The resolution limit for crystals of pyrophosphatase increased by almost 0.7 Angstrom, from 1.8 to 1.15 Angstrom.