Instrument Development to Reduce Radiation Damage in Macromolecular Crystallography

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This award is for developing instrumentation to reduce the deleterious effects of radiation damage in macromolecular crystallography, which is one of the major limitations in the this field. The instrumentation will be added to synchrotron radiation beamlines. Estimates of potential improvements in crystal survival are 60% for larger crystals and up to a factor of 10 for small platelet-shaped crystals. The basic idea of the strategies is to separate as much as possible the region where diffraction occurs from the region where the damage occurs. This possibility exists, because the primary cause of damage is the energetic photoelectrons (PE's) created by the absorption of x-rays through the photoelectric effect. In bio-crystals that predominantly contain low Z atoms the PE's will have energies about 500 eV less than those of the x-rays, thus typically up to 20 keV. For such energetic PE's the initial stopping power, namely, the energy loss per unit distance, is quite small and increases greatly as they slow down. The distance a 20 keV PE travels is 6 microns. Thus by concentrating the x-rays in small regions separated by slightly more than 6 microns, the goal of separating the diffraction and damaged regions can be accomplished. Any improvement in controlling or reducing primary radiation damage would have major impact on all of macromolecular x-ray crystallography, e.g., opening new crystallography for very large structures, increasing structure resolution of standard sized crystals and obtaining useful structure information from very small platelet-shaped crystals. By reducing damage to crystals during x-ray crystallography, this instrumentation will speed up the accumulation of crystal structures and the understanding of structure-function relationships of biological macromolecules. The project is interdisciplinary, involving physicists and a biologist, and international, involving a physicist from Israel.