Schultze Steffen, Grubmüller Helmut
Max Planck Institute for Multidisciplinary Sciences, Am Fassberg 11, Göttingen, Germany.
Sci Adv. 2024 Oct 25;10(43):eadp4425. doi: 10.1126/sciadv.adp4425.
Single molecule x-ray scattering experiments using free-electron lasers hold the potential to resolve biomolecular structures and structural ensembles. However, molecular electron density determination has so far not been achieved because of low photon counts, high noise levels, and low hit rates. Most approaches therefore focus on large specimen like entire viruses, which scatter sufficiently many photons to allow orientation determination of each image. Small specimens like proteins, however, scatter too few photons for the molecular orientations to be determined. Here, we present a rigorous Bayesian approach to overcome these limitations, additionally taking into account intensity fluctuations, beam polarization, irregular detector shapes, incoherent scattering, and background scattering. We demonstrate using synthetic scattering images that electron density determination of small proteins is possible in this extreme high noise Poisson regime. Tests on published virus data achieved the detector-limited resolution of 9 nm, using only 0.01% of the available photons per image.
使用自由电子激光进行的单分子X射线散射实验有潜力解析生物分子结构和结构集合体。然而，由于光子计数低、噪声水平高和命中率低，到目前为止尚未实现分子电子密度的测定。因此，大多数方法都集中在像整个病毒这样的大样本上，它们散射足够多的光子以允许确定每个图像的取向。然而，像蛋白质这样的小样本散射的光子太少，无法确定分子取向。在这里，我们提出一种严格的贝叶斯方法来克服这些限制，此外还考虑了强度波动、光束偏振、不规则探测器形状、非相干散射和背景散射。我们使用合成散射图像证明，在这种极端高噪声泊松 regime 中，确定小蛋白质的电子密度是可能的。对已发表的病毒数据进行的测试仅使用每个图像中0.01%的可用光子，就达到了探测器限制的9纳米分辨率。
