A crystal-processing machine using a deep-ultraviolet laser: application to long-wavelength native SAD experiments

While native SAD phasing is a promising method for next-generation macromolecular crystallography, it requires the collection of high-quality diffraction data using long-wavelength X-rays. The crystal itself and the noncrystalline medium around the crystal can cause background noise during long-wavelength X-ray data collection, hampering native SAD phasing. Optimizing the crystal size and shape or removing noncrystalline sample portions have thus been considered to be effective means of improving the data quality. A crystal-processing machine that uses a deep-UV laser has been developed. The machine utilizes the pulsed UV laser soft ablation (PULSA) technique, which generates less heat than methods using infrared or visible lasers. Since protein crystals are sensitive to heat damage, PULSA is an appropriate method to process them. Integration of a high-speed Galvano scanner and a high-precision goniometer enables protein crystals to be shaped precisely and efficiently. Application of this crystal-processing machine to a long-wavelength X-ray diffraction experiment significantly improved the diffraction data quality and thereby increased the success rate in experimental phasing using anomalous diffraction from atoms.