CRYO-EM MAP FILTERING

冷冻电镜图谱过滤

• 批准号: 7953781
• 负责人: MARC L BAKER
• 金额: $ 3.48万
• 依托单位: BAYLOR COLLEGE OF MEDICINE
• 依托单位国家: 美国
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-12-01 至 2009-11-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7953781
• 关键词: 3-Dimensional; Adopted; Algorithms; Capsid; Complement Factor B; Computer Retrieval of Information on Scientific Projects Database; Data; Electron Microscopy; Funding; Grant; Hepatitis B; Image; Institution; Maps; Overweight; Phase; Procedures; Process; Publications; Research; Research Personnel; Resolution; Resources; Source; Underweight; United States National Institutes of Health; Weight; Work; macromolecule; particle; programs; reconstruction

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. It is well recognized that the Fourier amplitudes of cryo-EM data are not as accurate as the corresponding phases. In general, low resolution amplitudes tend to be overweighted and high resolution amplitudes tend to be underweighted. The early work of Crowther showed that sharpening a map using a Gaussian function made the helices more pronounced in their 7.4 ¿ map of the hepatitis B capsid core (B¿ttcher et al., 1997). A similar approach has been adopted in many of the reconstruction maps (e.g. (Zhang et al., 2008b)). However, the actual B factor parameter used for sharpening those maps was somewhat ad hoc. In the EMAN procedure, when we merge the data in 2-D to make class-averages, we apply a Wiener filter (Ludtke et al., 2004). When 3-D reconstruction of these class-averages is performed, this Wiener filter is no longer fully accurate due to the additional averaging that occurs during reconstruction. This results in a moderate overfiltration of EMAN reconstructions before post-processing, even if all of the CTF parameters have been determined accurately. Similarly, the MPSA algorithm also includes a weighting factor of the experimental B factor for each particle image when they are merged through a modified EMAN 3D reconstruction program (Liu et al., 2007b). To compensate, we generally perform a refiltering (sharpening) of the map prior to final interpretation and publication. We are assessing different approaches as how to sharpen the map to bring out the hidden features.

该子项目是利用该技术的众多研究子项目之一 资源由 NIH/NCRR 资助的中心拨款提供。子项目及 研究者 (PI) 可能已从 NIH 的另一个来源获得主要资金， 因此可以在其他 CRISP 条目中表示。列出的机构是 对于中心来说，它不一定是研究者的机构。 众所周知，冷冻电镜数据的傅立叶振幅不如相应的相位准确。一般来说，低分辨率振幅往往​​被过度加权，而高分辨率振幅往往​​被低估。 Crowther 的早期工作表明，使用高斯函数锐化图谱可以使乙型肝炎衣壳核心 7.4 ¿ 图中的螺旋更加明显（B¿ttcher 等，1997）。许多重建图都采用了类似的方法（例如（Zhang et al., 2008b））。然而，用于锐化这些贴图的实际 B 因子参数在某种程度上是临时的。在 EMAN 过程中，当我们合并二维数据以获取类别平均值时，我们应用维纳滤波器（Ludtke et al., 2004）。当执行这些类平均值的 3-D 重建时，由于重建期间发生额外的平均，该维纳滤波器不再完全准确。即使所有 CTF 参数均已准确确定，这也会导致在后处理之前 EMAN 重建出现适度的过度过滤。类似地，当通过修改的 EMAN 3D 重建程序合并每个粒子图像时，MPSA 算法还包括每个粒子图像的实验 B 因子的加权因子（Liu 等人，2007b）。为了补偿，我们通常在最终解释和发布之前对地图进行重新过滤（锐化）。我们正在评估如何锐化地图以显示隐藏特征的不同方法。