STUDY OF RADIATION DECAY OF PROTEIN CRYSTALS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The high-flux beam lines at third generation synchrotrons produce very high intensity x-radiation. Unfortunately, due to decay of the protein crystals in the high intensity beam, the synchrotrons have to use attenuators to reduce the beam intensity. Therefore, beam lines are not utilizing their full potential for protein diffraction experiments. There have been several attempts to study the mechanisms of protein crystal decay. However, this area of study is still in its infancy. The common belief is that the radiation decay is partly due to the effect of the radicals produced by the interaction of x-ray photons with the protein or solvent atoms in the crystal. Researchers have used various procedures like lowering the data collection temperature, incorporating radical scavengers, etc. to reduce the effect of these radicals. The current study tries to address the radiation decay of protein crystals by employing few selected gases as radical scavengers. This is the first study of this kind and the preliminary results underscore the usefulness of this method. Several protein crystals were used for this study. To reduce the effect of crystal size, this study employed crystals with similar sizes. The data sets were collected at three strong beam lines at SSRL. Continuous decay data were taken for several control crystals and for several crystals exposed to a one of the gases. The primary metric used for calculating the damage accrual rate at a given resolution was the change in I/sigma value reported by MOSFLM over the time range of the data set. 115 GB of diffraction data has been collected and analyzed with scripts written specifically for this purpose. Some of the selected gases showed reduced radiation decay.