Damage by X-rays: A Case Study for Metallo-Protein Crystallography

Fig. 1. Mn XANES and EXAFS of single crystals of photosystem II as a function of x-ray dose. As the x-ray dose increases, Mn in PS II normally present as Mn4(III2,IV2) is reduced to Mn(II) as seen by the changes in XANES spectra (left bottom). The changes in the corresponding EXAFS spectra (right) show that the three Fourier peaks characteristic of Mn-bridging-oxo, Mn-terminal, and Mn-Mn/Ca interactions (dashed vertical line) are replaced by one Fourier peak characteristic of a Mn(II) environment. A PS II crystal subsequent to x-ray exposure is also shown (left top). The bright green color is from the chlorophyll molecules in PS II and the dark spots show the areas of the crystal used for x-ray diffraction data collection. Damage by X-rays: A Case Study for Metallo-Protein Crystallography