Stark H, Mueller F, Orlova E V, Schatz M, Dube P, Erdemir T, Zemlin F, Brimacombe R, van Heel M
Fritz Haber Institute of the Max Planck Society, Berlin, Germany.
Structure. 1995 Aug 15;3(8):815-21. doi: 10.1016/s0969-2126(01)00216-7.
The ribosome--essential for protein synthesis in all organisms--has been an evasive target for structural studies. The best available structures for the 70S Escherichia coli ribosome or its 30S and 50S subunits are based on electron microscopical tilt experiments and are limited in resolution to 28-55 A. The angular reconstitution approach, which exploits the random orientations of particles within a vitreous ice matrix, can be used in conjunction with cryo-electron microscopy to yield a higher-resolution structure.
Our 23 A resolution map of the 70S ribosome elucidates many structural details, such as an extensive system of channels within the 50S subunit and an intersubunit gap ideally shaped to accommodate two transfer RNA molecules. The resolution achieved is sufficient to allow the preliminary fitting of double-helical regions of an earlier three-dimensional ribosomal RNA model.
Although we are still a long way from attaining an atomic-resolution structure of the ribosome, cryo-electron microscopy, in combination with angular reconstitution, is likely to yield three-dimensional maps with gradually increasing resolution. As exemplified by our current 23 A reconstruction, these maps will lead to progressive refinement of models of the ribosomal RNA.
核糖体——所有生物体蛋白质合成所必需的——一直是结构研究中难以捉摸的目标。70S大肠杆菌核糖体或其30S和50S亚基目前可得的最佳结构是基于电子显微镜倾斜实验，分辨率限制在28 - 55埃。角重构方法利用玻璃态冰基质内颗粒的随机取向，可与冷冻电子显微镜结合使用以产生更高分辨率的结构。
我们得到的70S核糖体23埃分辨率图谱阐明了许多结构细节，例如50S亚基内广泛的通道系统以及亚基间间隙，其形状非常适合容纳两个转运RNA分子。所达到的分辨率足以对早期三维核糖体RNA模型的双螺旋区域进行初步拟合。
尽管我们距离获得核糖体的原子分辨率结构仍有很长的路要走，但冷冻电子显微镜结合角重构方法可能会产生分辨率逐渐提高的三维图谱。正如我们目前23埃分辨率重构所示，这些图谱将促使核糖体RNA模型不断完善。
