Brandt Florian, Etchells Stephanie A, Ortiz Julio O, Elcock Adrian H, Hartl F Ulrich, Baumeister Wolfgang
Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Am Klopferspitz 18, Martinsried 82152, Germany.
Cell. 2009 Jan 23;136(2):261-71. doi: 10.1016/j.cell.2008.11.016.
Recent advances have led to insights into the structure of the bacterial ribosome, but little is known about the 3D organization of ribosomes in the context of translating polysomes. We employed cryoelectron tomography and a template-matching approach to map 70S ribosomes in vitrified bacterial translation extracts and in lysates of active E. coli spheroplasts. In these preparations, polysomal arrangements were observed in which neighboring ribosomes are densely packed and exhibit preferred orientations. Analysis of characteristic examples of polysomes reveals a staggered or pseudohelical organization of ribosomes along the mRNA trace, with the transcript being sequestered on the inside, the tRNA entrance sites being accessible, and the polypeptide exit sites facing the cytosol. Modeling of elongating nascent polypeptide chains suggests that this arrangement maximizes the distance between nascent chains on adjacent ribosomes, thereby reducing the probability of intermolecular interactions that would give rise to aggregation and limit productive folding.
最近的进展使人们对细菌核糖体的结构有了深入了解，但对于正在翻译的多核糖体环境中核糖体的三维组织却知之甚少。我们采用冷冻电子断层扫描和模板匹配方法，对玻璃化细菌翻译提取物和活性大肠杆菌原生质体裂解物中的70S核糖体进行定位。在这些制剂中，观察到多核糖体排列，其中相邻核糖体紧密堆积并呈现出偏好的方向。对多核糖体特征实例的分析揭示了核糖体沿mRNA轨迹呈交错或假螺旋排列，转录本被隔离在内部，tRNA进入位点可及，多肽出口位点面向细胞质。对正在延伸的新生多肽链的建模表明，这种排列使相邻核糖体上新生链之间的距离最大化，从而降低了分子间相互作用导致聚集并限制有效折叠的可能性。
