A Peltier-cooled microscope stage for protein crystal post-crystallization treatment

Crystals of the multi-enzyme complex hydrazine synthase showed severe diffuse scattering and high mosaicity. Improved diffraction quality was achieved by soaking the crystals in highly concentrated betaine solutions at reduced temperatures. To enable this, a Peltier-cooled microscope stage was developed for the slow cooling of protein crystals immersed in cryoprotectants or other soaking solutions. Both the construction of the stage and its successful application to hydrazine synthase crystals are described.