Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, The Netherlands.
Faraday Discuss. 2022 Nov 8;240(0):168-183. doi: 10.1039/d2fd00078d.
Resolution-dependent loss of contrast in cryo-EM maps may obscure features at high resolution that are critical for map interpretation. Post-processing of cryo-EM maps can improve the interpretability by adjusting the resolution-dependence of structure factor amplitudes through map sharpening. Traditionally this has been done by rescaling the relative contribution of low and high-resolution frequencies globally. More recently, the realisation that molecular motion and heterogeneity cause non-uniformity of resolution throughout the map has inspired the development of techniques that optimise sharpening locally. We previously developed , a method that utilises the radial structure factor from a refined atomic model as a restraint for local map sharpening. While this method has proved beneficial for the interpretation of cryo-EM maps, the dependence on the availability of (partial) model information limits its general applicability. Here, we review the basic assumptions of resolution-dependent contrast loss in cryo-EM maps and propose a route towards a robust alternative for local map sharpening that utilises information on expected scattering properties of biological macromolecules, but requires no detailed knowledge of the underlying molecular structure. We examine remaining challenges for implementation and discuss possible applications.
低温电子显微镜（cryo-EM）映射中的对比度分辨率依赖性损失可能会掩盖高分辨率下对映射解释至关重要的特征。通过通过锐化映射来调整结构因子幅度的分辨率依赖性，可以对低温电子显微镜映射进行后处理，以提高可解释性。传统上，这是通过全局重新缩放低分辨率和高分辨率频率的相对贡献来完成的。最近，人们意识到分子运动和异质性会导致整个映射中分辨率的不均匀性，这激发了开发局部优化锐化技术的灵感。我们之前开发了一种方法，该方法利用来自经过精制的原子模型的径向结构因子作为局部地图锐化的约束。虽然该方法已被证明对低温电子显微镜映射的解释有益，但对（部分）模型信息可用性的依赖限制了其广泛适用性。在这里，我们回顾了低温电子显微镜映射中对比度分辨率依赖性损失的基本假设，并提出了一种稳健的替代方法，用于局部地图锐化，该方法利用了有关生物大分子预期散射特性的信息，但不需要对基础分子结构有详细的了解。我们检查了实施的剩余挑战，并讨论了可能的应用。
