Crystallization and cryocrystallography inside X-ray capillaries

This paper presents a modification of the gel acupuncture method to grow isolated crystals inside X-ray capillaries. Protein crystals are grown from 2-12 µl of gelled agarose-protein solution, cryoprotected and immobilized by the gel matrix. The same X-ray capillary that acts as a crystallization reactor is used to transport the crystals to the X-ray source and to collect data at both room temperature and 100 K, without any post-crystallization manipulation. To enhance the flash-cooling stage, two additional elements are proposed for inclusion in the cryosystems currently in use: a laser pointer to illuminate the crystal to be flash-cooled and a trap to divert the N₂ flow and switch from room temperature to 100 K without misalignment of the crystal. With the proposed implementation, data can be collected at different temperatures from the same crystal in exactly the same orientation. This permits the study, at lattice level, of changes in unit-cell parameters, mosaic spread and crystal quality induced by cryogenic temperatures and annealing techniques.