FACILITY CHARACTERIZATION FOR ANOMALOUS SOLUTION X-RAY SCATTERING IN STRUCTURAL

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 SPEAR3升级提供了显著改善的束流特性，特别是改善了束流亮度和稳定性，为重新审视结构生物学中一些极具挑战性的X射线散射研究提供了极好的机会。最近在使用人工引入的反常散射体，即主要用于单晶衍射研究的SeMe和Au团簇方面的进展，重新引起了人们对反常溶液散射研究的兴趣，过去使用自然发生的反常散射元素进行的研究取得的成功有限。作为SSRL近20年来的第一个可行性研究，我们在Fe-K吸收边(7113 EV)对马脾铁蛋白进行了反常蛋白质溶液散射实验。我们成功地探测到了反常散射效应，重现了Stuhrmann(Acta Cryst A36,996-1001,1980)报道的主要结果。简单地说，我们记录了在K边的旋转半径(Rg)从36°到37.6°的明显偏转，这与定位在分子外围的Fe物种的高对比度一致。这也证明了我们的单色仪的能量分辨率和数小时内约0.6 eV的能量稳定性对于反常散射研究是足够的。我们的结果与公布的44°和42°的值是一致的。在我们的实验中，我们解释了Rg值的差异是由于较高的蛋白质浓度引起的较高水平的颗粒间干扰。我们对这一结果感到鼓舞，并计划在更低的金属浓度下研究更具挑战性的蛋白质系统。我们正在整合辐射探测器技术？S涡旋能量分辨探测器(在上一次拨款年度结束时购买)，用于荧光模式下的吸收边测量。

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 significantly improved beam characteristics provided by the SPEAR3 upgrade, in particular improved beam brightness and stability, provide an excellent opportunity for revisiting some of the highly challenging x-ray scattering studies in structural biology. Recent advances in the use of artificially introduced anomalous scatterers, namely SeMet and Au-clusters primarily developed for single crystal diffraction studies, have brought renewed interests in anomalous solution scattering studies, which has had limited success in the past using naturally occurring anomalous scattering elements. As the first feasibility study at SSRL in nearly two decades, we conducted anomalous protein solution scattering experiments on horse spleen ferritin at the Fe K absorption edge (7113 eV). We successfully detected the anomalous scattering effect, reproducing the principal results reported by Stuhrmann (Acta Cryst A36, 996-1001, 1980). Briefly described, we recorded clear deflection in the radius of gyration (Rg) to 37.6 ¿ at the K edge from 36 ¿, consistent with the higher contrast of Fe species which are localized in the periphery of the molecule. This also demonstrates that the energy resolution of our monochromator and the energy stability of ca 0.6 eV over several hours are adequate for anomalous scattering studies. Our result is consistent with the published values of 44 ¿ and 42 ¿. We interpret the difference in Rg values due to a higher level of interparticle interference caused by the higher protein concentration in our experiments. We are encouraged by this result, and plan on studying more challenging protein systems at more dilute metal concentrations. We are in the process of incorporating the Radiant Detector Technology¿s Vortex-EX energy resolving detector (purchased at the end of the last grant year) for absorption edge measurements in fluorescence mode.