FACILITY CHARACTERIZATION FOR ANOMALOUS SOLUTION X-RAY SCATTERING IN STRUCTURAL

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。子项目和 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。 SPEAR 3升级提供的显著改进的光束特性，特别是改进的光束亮度和稳定性，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绝佳的机会。最近的进展，在使用人工引入的异常散射体，即SeMet和Au簇主要开发用于单晶衍射研究，带来了新的兴趣在异常溶液散射研究，这在过去使用自然发生的异常散射元素的成功有限。 作为SSRL近二十年来的第一项可行性研究，我们在铁钾吸收边（7113 eV）对马脾铁蛋白进行了异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，再现了Stuhrmann（Acta Cryst A36，996-1001，1980）报道的主要结果。简单地说，我们记录了清晰的偏转在回转半径（Rg）从36到37.6在K边缘，与Fe物种的较高的对比度，这是本地化在分子的外围一致。这也表明，我们的单色仪的能量分辨率和能量稳定性约0.6 eV的几个小时是足够的异常散射研究。我们的结果与公布的44 <$和42 <$的值一致。我们解释Rg值的差异是由于实验中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，并计划在更稀的金属浓度下研究更具挑战性的蛋白质系统。我们正在将辐射探测器技术公司的涡旋EX能量分辨探测器（在上一个资助年度年底购买）纳入荧光模式的吸收边测量。

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.