Laser-improved protein crystallization screening

The effect of laser irradiation on freshly prepared protein drops was explored and found to be a viable tool to induce nucleation. In our experiment, the number of positive crystallization hits during the screening process increased. In some instances the speed of crystal growth, the size of the crystals and the resolution of X-ray diffraction showed a marked improvement after laser exposure. Under optimized laser settings, in no case was the laser detrimental to crystal growth. Screening of proteins for crystallization under laser irradiation was investigated using six proteins: ribonuclease B, glucose dehydrogenase, lysozyme, sorbitol dehydrogenase, fructose dehydrogenase and myoglobin. Shining 532 nm green circularly polarized laser light with a picosecond pulse and 6 mW power for 30 s on newly set-up protein drops showed a marked improvement in the number of screen conditions amenable for crystal growth compared with control drops under identical conditions but without laser exposure. For glucose dehydrogenase and sorbitol dehydrogenase, larger and better quality crystals were formed and the resolution of X-ray diffraction was improved. The speed of crystallization increased in the case of ribonuclease B, lysozyme and sorbitol dehydrogenase. During laser irradiation, the amount of precipitation in the screened drops increased, indicating a transient decrease in protein solubility. At the optimized laser settings, there was no deleterious effect of the laser on crystal growth or on the protein. In the cases of ribonuclease B and lysozyme the crystal packing did not change owing to the laser exposure