Insights into the mechanism of X-ray induced structural perturbation of macromolecules

This dissertation focuses on the structural changes induced by X-rays during macromolecular crystallographic data collection. This damage cannot be prevented and often leads to degradation in the data quality, which can affect the resulting structure and thus the biological interpretation. The aim of this research was to understand the radiation chemistry of the damage process. This includes the protein components most susceptible to damage, the disulfide bond and metal atoms. By providing some insight into the mechanism for disulfide bond cleavage and the role the active site metal and its surrounding environment plays in the extent of the damage that occurs we have proposed an initial, generalized model for radiation damage. The results indicate that this multi-track process is due to the overlap of two one-electron reductions or two one-electron oxidations. A reaction scheme for the most susceptible residues (cystine, cysteine, methionine, aspartate, glutamate and tyrosine) is provided with experimental evidence of the predicted damage from crystallographic data collected on lysozyme and xylose isomerase.