Crystallization and cryocrystallography inside X-ray capillaries

This paper presents a modification of the gel acupuncture method to grow is olated crystals inside X-ray capillaries. Protein crystals are grown from 2 -12 mul of gelled agarose-protein solution, cryoprotected and immobilized b y the gel matrix. The same X-ray capillary that acts as a crystallization r eactor 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 a re proposed for inclusion in the cryosystems currently in use: a laser poin ter to illuminate the crystal to be flash-cooled and a trap to divert the N -2 flow and switch from room temperature to 100 K without misalignment of t he crystal. With the proposed implementation, data can be collected at diff erent temperatures from the same crystal in exactly the same orientation. T his permits the study, at lattice level, of changes in unit-cell parameters , mosaic spread and crystal quality induced by cryogenic temperatures and a nnealing techniques.