STUDY OF RADIATION DECAY OF PROTEIN CRYSTALS

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目及 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 第三代同步加速器的高通量光束线产生非常高强度的x射线辐射。不幸的是，由于高强度光束中蛋白质晶体的衰减，同步加速器必须使用衰减器来降低光束强度。 因此，光束线没有充分利用其在蛋白质衍射实验中的潜力。 已经有几次尝试来研究蛋白质晶体衰变的机制。 然而，这一领域的研究仍处于起步阶段。一般认为，辐射衰减部分是由于X射线光子与晶体中的蛋白质或溶剂原子相互作用产生的自由基的影响。 研究人员已经使用了各种程序，如降低数据收集温度，加入自由基清除剂等，以减少这些自由基的影响。目前的研究试图解决辐射衰变的蛋白质晶体采用少数选定的气体作为自由基清除剂。 这是第一次进行这种研究，初步结果强调了这种方法的实用性。 本研究使用了几种蛋白质晶体。为了减少晶体尺寸的影响，本研究采用了具有相似尺寸的晶体。 这些数据集是在SSRL的三条强束线上收集的。 对几个对照晶体和暴露于其中一种气体的几个晶体进行连续衰减数据。用于计算给定分辨率下的损伤累积率的主要指标是在数据集的时间范围内由CNOLM报告的I/sigma值的变化。已经收集了115 GB的衍射数据，并使用专门为此目的编写的脚本进行分析。一些选定的气体显示出减少的辐射衰变。

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.