Improved Algorithms for Macromolecular Structure Determination by cyro-EM

描述（由申请人提供）：单粒子电子低温显微镜（cryo-EM）是一种观察大型大分子三维结构的方法。在低温电镜中，实验数据是由大分子“粒子”的噪声、随机投影图像组成的，问题是找到与这些图像一致的三维结构。该提案旨在开发并应用于实验数据的新算法来解决由结构生物学技术提出的两个困难的数学问题。首先，经典的低温电镜重建技术假设粒子是相同的。然而，在许多数据集中，这种假设并不成立。一些感兴趣的分子有不止一种构象态。生物学家对这些结构变化非常感兴趣，因为它们提供了对分子功能的深入了解。这个项目的第一个调查领域是开发

DESCRIPTION (provided by applicant): Single-particle electron cryomicroscopy (cryo-EM) is a method for observing the three- dimensional structures of large macromolecules. In cryo-EM the experimental data consist of noisy, random projection images of macromolecular "particles", and the problem is finding the 3D structure which is consistent with these images. The proposal aims to develop and apply to experimental data novel algorithms for solving two difficult mathematical problems posed by this technique of structural biology. First, classical cryo-EM reconstruction techniques assume that the particles are identical. However, in many datasets this assumption does not hold. Some molecules of interest have more than one conformational state. These structural variations are of great interest to biologists, as they provide insight int the functioning of the molecule. The first area of investigation in this project is the development of algorithmic and mathematical framework for determining structures associated with heterogeneous particle populations. The proposed algorithm is not only faster than existing techniques but is also mathematically provable to reveal the different conformations if the number of images is sufficiently large. Second, a major limiting factor for present cryo-EM studies is the particle size. Images of small particles are often too noisy for existing methods to provide valid three-dimensional reconstructions; although the images contain structural information, the assignment of orientations to the individual particles is unreliable. The second area of investigation focuses on developing a radical new approach for reconstruction of small particles without the need for determining particle orientations.