Life Sciences Division, Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
Biopolymers. 2011 Aug;95(8):559-71. doi: 10.1002/bip.21638. Epub 2011 Apr 20.
Unstructured proteins, RNA or DNA components provide functionally important flexibility that is key to many macromolecular assemblies throughout cell biology. As objective, quantitative experimental measures of flexibility and disorder in solution are limited, small angle scattering (SAS), and in particular small angle X-ray scattering (SAXS), provides a critical technology to assess macromolecular flexibility as well as shape and assembly. Here, we consider the Porod-Debye law as a powerful tool for detecting biopolymer flexibility in SAS experiments. We show that the Porod-Debye region fundamentally describes the nature of the scattering intensity decay by capturing the information needed for distinguishing between folded and flexible particles. Particularly for comparative SAS experiments, application of the law, as described here, can distinguish between discrete conformational changes and localized flexibility relevant to molecular recognition and interaction networks. This approach aids insightful analyses of fully and partly flexible macromolecules that is more robust and conclusive than traditional Kratky analyses. Furthermore, we demonstrate for prototypic SAXS data that the ability to calculate particle density by the Porod-Debye criteria, as shown here, provides an objective quality assurance parameter that may prove of general use for SAXS modeling and validation.
无规蛋白、RNA 或 DNA 成分提供了功能上重要的灵活性，这是细胞生物学中许多大分子组装的关键。由于对溶液中灵活性和无序性的客观、定量实验测量受到限制，小角散射（SAS），特别是小角 X 射线散射（SAXS），为评估大分子灵活性以及形状和组装提供了关键技术。在这里，我们将 Porod-Debye 定律视为在 SAS 实验中检测生物聚合物灵活性的强大工具。我们表明，Porod-Debye 区域通过捕获区分折叠和灵活粒子所需的信息，从根本上描述了散射强度衰减的性质。特别是对于比较性 SAS 实验，这里描述的定律的应用可以区分离散构象变化和与分子识别和相互作用网络相关的局部灵活性。这种方法有助于对完全和部分灵活的大分子进行有洞察力的分析，比传统的 Kratky 分析更稳健、更具结论性。此外，我们用典型的 SAXS 数据证明，如这里所示，通过 Porod-Debye 标准计算粒子密度的能力提供了一个客观的质量保证参数，这可能对 SAXS 建模和验证具有普遍的用途。
