Institute for Protein Research, Osaka University, Suita, Osaka, Japan.
Adv Exp Med Biol. 2018;1105:219-235. doi: 10.1007/978-981-13-2200-6_14.
Cryo electron microscopy has revolutionarily evolved for the determination of the 3D structure of macromolecular complexes. The modeling procedures on the 3D density maps of electron microscopy are roughly classified into three categories: fitting, de novo modeling and refinement. The registered atomic models from the maps have mostly been hand-built and auto-refined. Several programs aiming at automatic modeling have also been developed using various kinds of molecular representations. Among these three classes of the modeling procedures, the rigid body fitting is reviewed here, because it is the most basic modeling process applied before the other steps. The fitting problems are classified as the fittings of single subunit or multiple subunits, and the fittings on global or local parts of maps. A higher resolution map enables more local fitting. Various molecular representations have been employed in the fitting programs. A point and digital image models are generally used to represent molecules, but new representations, such as the Gaussian mixture model, have been applied recently.
低温电子显微镜技术的发展极大地促进了生物大分子复合物三维结构的测定。在电子显微镜 3D 密度图上进行建模的过程大致可以分为三类：拟合、从头建模和精修。从图谱中提取的已注册原子模型主要通过手动构建和自动精修得到。目前已经开发出了一些使用不同分子表示形式的自动建模程序。在这三种建模过程中，本文主要介绍刚体拟合，因为它是其他步骤之前应用的最基本的建模过程。拟合问题可分为单个亚基或多个亚基的拟合，以及图谱全局或局部区域的拟合。更高的分辨率图谱可以实现更多的局部拟合。在拟合程序中使用了各种分子表示形式。点和数字图像模型通常用于表示分子，但最近也应用了新的表示形式，如高斯混合模型。
