Department of Biology, ETH Zurich, Zurich 8093, Switzerland.
Department of Chemistry and Biochemistry, University of Bern, Bern 3012, Switzerland.
Mol Cell. 2020 Aug 20;79(4):629-644.e4. doi: 10.1016/j.molcel.2020.06.030. Epub 2020 Jul 16.
In contrast to the bacterial translation machinery, mitoribosomes and mitochondrial translation factors are highly divergent in terms of composition and architecture. There is increasing evidence that the biogenesis of mitoribosomes is an intricate pathway, involving many assembly factors. To better understand this process, we investigated native assembly intermediates of the mitoribosomal large subunit from the human parasite Trypanosoma brucei using cryo-electron microscopy. We identify 28 assembly factors, 6 of which are homologous to bacterial and eukaryotic ribosome assembly factors. They interact with the partially folded rRNA by specifically recognizing functionally important regions such as the peptidyltransferase center. The architectural and compositional comparison of the assembly intermediates indicates a stepwise modular assembly process, during which the rRNA folds toward its mature state. During the process, several conserved GTPases and a helicase form highly intertwined interaction networks that stabilize distinct assembly intermediates. The presented structures provide general insights into mitoribosomal maturation.
与细菌翻译机制相比，线粒体核糖体和线粒体翻译因子在组成和结构上存在高度差异。越来越多的证据表明，线粒体核糖体的生物发生是一个复杂的途径，涉及许多组装因子。为了更好地理解这个过程，我们使用低温电子显微镜研究了来自人体寄生虫布氏锥虫的线粒体核糖体大亚基的天然组装中间体。我们鉴定了 28 种组装因子，其中 6 种与细菌和真核核糖体组装因子同源。它们通过特异性识别功能重要区域（如肽基转移酶中心）与部分折叠的 rRNA 相互作用。组装中间体的结构和组成比较表明，在这个过程中，rRNA 朝着成熟状态折叠，是一个逐步模块化的组装过程。在此过程中，几种保守的 GTPase 和解旋酶形成高度交织的相互作用网络，稳定不同的组装中间体。所呈现的结构为线粒体核糖体成熟提供了一般性的见解。
