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Femtosecond X-ray Protein Nanocrystallography & Correlated Fluctuation Small-Angle X-ray Scattering.

机译：飞秒X射线蛋白质纳米晶体学和相关的涨落小角度X射线散射。

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摘要

With the advent of the X-ray free-electron laser (XFEL), an opportunity has arisen to break the nexus between radiation dose and spatial resolution in diffractive imaging, by outrunning radiation damage altogether when using single X-ray pulses so brief that they terminate before atomic motion commences. This dissertation concerns the application of XFELs to biomolecular imaging in an effort to overcome the severe challenges associated with radiation damage and macroscopic protein crystal growth. The method of femtosecond protein nanocrystallography (fsPNX) is investigated, and a new method for extracting crystallographic structure factors is demonstrated on simulated data and on the first experimental fsPNX data obtained at an XFEL. Errors are assessed based on standard metrics familiar to the crystallography community. It is shown that resulting structure factors match the quality of those measured conventionally, at least to 9 angstrom resolution. A new method for ab-initio phasing of coherently-illuminated nanocrystals is then demonstrated on simulated data. The method of correlated fluctuation small-angle X-ray scattering (CFSAXS) is also investigated as an alternative route to biomolecular structure determination, without the use of crystals. It is demonstrated that, for a constrained two-dimensional geometry, a projection image of a single particle can be formed, ab-initio and without modeling parameters, from measured diffracted intensity correlations arising from disordered ensembles of identical particles illuminated simultaneously. The method is demonstrated experimentally, based on soft X-ray diffraction from disordered but identical nanoparticles, providing the first experimental proof-of-principle result. Finally, the fundamental limitations of CFSAXS is investigated through both theory and simulations. It is found that the signal-to-noise ratio (SNR) for CFSAXS data is essentially independent of the number of particles exposed in each diffraction pattern. The dependence of SNR on particle size and resolution is considered, and realistic estimates are made (with the inclusion of solvent scatter) of the SNR for protein solution scattering experiments utilizing an XFEL source.
机译：随着X射线自由电子激光器（XFEL）的出现，出现了一种在衍射成像中打破辐射剂量和空间分辨率之间联系的机会，因为当使用单个X射线脉冲时，它们完全要克服辐射损伤，因此它们必须短暂。在原子运动开始之前终止。本论文涉及XFEL在生物分子成像中的应用，以克服与辐射损伤和宏观蛋白质晶体生长相关的严峻挑战。研究了飞秒蛋白质纳米晶体学（fsPNX）的方法，并在模拟数据和XFEL上获得的第一个实验性fsPNX数据上演示了一种提取晶体结构因子的新方法。根据晶体学界熟悉的标准指标评估错误。结果表明，所得的结构因子至少与9埃分辨率相匹配，与常规测量的结果相符。然后在模拟数据上证明了相干照明的纳米晶体从头开始定相的新方法。还研究了相关起伏小角X射线散射（CFSAXS）方法，作为不使用晶体确定生物分子结构的另一种方法。已经证明，对于受约束的二维几何形状，可以从同时照射相同粒子的无序集合产生的测量衍射强度相关性中，从头开始并且没有建模参数，可以形成单个粒子的投影图像。该方法基于无序但相同的纳米粒子的软X射线衍射进行了实验验证，提供了第一个实验原理证明结果。最后，通过理论和仿真研究了CFSAXS的基本局限性。发现CFSAXS数据的信噪比（SNR）基本上与每个衍射图样中暴露的颗粒数无关。考虑了SNR对粒度和分辨率的依赖性，并针对使用XFEL来源的蛋白质溶液散射实验对SNR进行了实际估算（包括溶剂分散）。

著录项

  • 作者

    Kirian, Richard A.;

  • 作者单位

    Arizona State University.;

  • 授予单位 Arizona State University.;
  • 学科 Physics Optics.;Biophysics General.
  • 学位 Ph.D.
  • 年度 2011
  • 页码 227 p.
  • 总页数 227
  • 原文格式 PDF
  • 正文语种 eng
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  • 关键词

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