Cryo-electron microscopy using single particle analysis requires the computational averaging of thousands of projection images captured from identical macromolecules. However, macromolecules usually present some degree of flexibility showing different conformations. Computational approaches are then required to classify heterogeneous single particle images into homogeneous sets corresponding to different structural states. Nonetheless, sometimes the attainable resolution of reconstructions obtained from these smaller homogeneous sets is compromised because of reduced number of particles or lack of images at certain macromolecular orientations. In these situations, the current solution to improve map resolution is returning to the electron microscope and collect more data. In this work, we present a fast approach to partially overcome this limitation for heterogeneous data sets. Our method is based on deforming and then moving particles between different conformations using an optical flow approach. Particles are then merged into a unique conformation obtaining reconstructions with improved resolution, contrast and signal-to-noise ratio. We present experimental results that show clear improvements in the quality of obtained 3D maps, however, there are also limits to this approach, i.e., the method is restricted to small deformations and cannot determine local patterns of flexibility of small elements, such as secondary structures, which we discuss in the manuscript.

使用单粒子分析的冷冻电子显微镜需要对从相同大分子捕获的数千个投影图像进行计算平均。然而，大分子通常表现出一定程度的灵活性，显示出不同的构象。然后需要计算方法将异质单粒子图像分类为对应于不同结构状态的同质集。尽管如此，有时由于粒子数量减少或在某些大分子方向缺乏图像，从这些较小的同质集合中获得的重建的可达到的分辨率会受到影响。在这些情况下，当前提高地图分辨率的解决方案是返回电子显微镜并收集更多数据。在这项工作中，我们提出了一种快速方法来部分克服异构数据集的这种限制。我们的方法基于变形，然后使用光流方法在不同构象之间移动粒子。然后将粒子合并成独特的构象，从而获得分辨率、对比度和信噪比得到改善的重建。我们提出的实验结果表明获得的 3D 地图的质量有明显的提高，但是，这种方法也有局限性，即该方法仅限于小变形，无法确定小元素（例如二级结构）的局部柔性模式，我们在手稿中讨论。然后将粒子合并成独特的构象，从而获得分辨率、对比度和信噪比得到改善的重建。我们提出的实验结果表明获得的 3D 地图的质量有明显的提高，但是，这种方法也有局限性，即该方法仅限于小变形，无法确定小元素（例如二级结构）的局部柔性模式，我们在手稿中讨论。然后将粒子合并成独特的构象，从而获得分辨率、对比度和信噪比得到改善的重建。我们提出的实验结果表明获得的 3D 地图的质量有明显的提高，但是，这种方法也有局限性，即该方法仅限于小变形，无法确定小元素（例如二级结构）的局部柔性模式，我们在手稿中讨论。