X-rays-Induced Cooperative Atomic Movement in a Protein Crystal

Protein molecules are damaged during X-ray diffraction experiments with protein crystals, which is in many cases a serious hindrance to structure solution. It is still not well understood whether radiation-induced local chemical changes lead to global structural changes in protein and what the mechanism is. We present experimental evidence at atomic resolution that irradiation causes the displacement of big parts of the protein molecule and water network. Radiation-induced structural changes in a protein molecule were studied in a series of diffraction experiments in which multiple data sets corresponding to increasing absorbed doses were collected from the same crystals of human aldose reductase (h-AR) and elastase at atomic resolution. There is a pronounced correlation between collective atomic movements and local and global damage to the crystal. Radiation-induced atomic shifts start at places with the pronounced local damage and are the largest for the damaged residues and structure fragments connected to damaged residues. An analysis of atomic displacement parameters (ADPs) revealed a distinct increase in the anisotropic character of ADP’s for the atoms of some segments of the structures. This effect was pronounced for those atoms that initially had approximately isotropic ADPs and shifted over relatively large distances during irradiation. Because their displacements in different cells of the crystal occur not exactly at the same moment, this leads to an additional static disorder component.