Investigation of long-range order in protein crystals by X-ray diffraction

The rate and mechanisms of growth and the final quality of crystals are related to lattice disorders and can be studied from the analysis of X-ray diffraction patterns. Crystals of proteins and other biological macromolecules display features which are different from those of inorganic crystals. In this work the long-range order of protein crystals is probed via the mosaic spread, with a special camera constructed for this purpose. The very small mosaic spread measured indicates almost perfect long-range order in the crystal, suggesting the absence of dislocations. This is compatible with the weak binding energies and mechanical softness of protein crystals. If indeed such crystals do not incorporate dislocations, accumulation of strain may be a possible mechanism for the cessation of growth of protein crystals. Microscopic observations of crystal growth support this idea.