In-situ measurement of rocking curves during lysozyme crystal growth

The rocking curve of protein crystals contains a lot of useful information concerning crystal quality, most of which is lost owing to the superimposit ion of spurious features appearing in these fragile materials after growth, during handling and mounting. To minimize such data spoiling, an experimen tal setup to perform in situ X-ray diffraction experiments during crystal g rowth has been designed. The setup, which includes video observation to all ow the correlation of crystal shape, size and growth rate with X-ray data, has been used to assess the mosaicity of tetragonal lysozyme crystals durin g crystal growth. The full width at half maximum (FWHM) of diffraction peak s collected from these crystals changes during the growth process as a (dir ectly proportional) response to the growth rates and the different developm ent of different domain blocks. These changes in the domain distribution an d FWHM with time involve a 'zonation' of the crystals, which show very diff erent rocking curves in different parts of their volume. The rocking curves recorded in situ from growing crystals are easier to understand than those from crystals that have suffered even ruiner handling.