Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada.
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, USA.
Nat Struct Mol Biol. 2023 Oct;30(10):1468-1480. doi: 10.1038/s41594-023-01078-5. Epub 2023 Aug 31.
Ribosome assembly is orchestrated by many assembly factors, including ribosomal RNA methyltransferases, whose precise role is poorly understood. Here, we leverage the power of cryo-EM and machine learning to discover that the E. coli methyltransferase KsgA performs a 'proofreading' function in the assembly of the small ribosomal subunit by recognizing and partially disassembling particles that have matured but are not competent for translation. We propose that this activity allows inactive particles an opportunity to reassemble into an active state, thereby increasing overall assembly fidelity. Detailed structural quantifications in our datasets additionally enabled the expansion of the Nomura assembly map to highlight rRNA helix and r-protein interdependencies, detailing how the binding and docking of these elements are tightly coupled. These results have wide-ranging implications for our understanding of the quality-control mechanisms governing ribosome biogenesis and showcase the power of heterogeneity analysis in cryo-EM to unveil functionally relevant information in biological systems.
核糖体组装由许多组装因子协调，包括核糖体 RNA 甲基转移酶，其确切作用尚不清楚。在这里，我们利用 cryo-EM 和机器学习的力量发现，大肠杆菌甲基转移酶 KsgA 通过识别和部分拆解已经成熟但不具备翻译能力的颗粒，在小核糖体亚基的组装中发挥“校对”功能。我们提出，这种活性使非活性颗粒有机会重新组装成活性状态，从而提高整体组装保真度。我们数据集的详细结构定量分析还扩展了 Nomura 组装图谱，以突出 rRNA 螺旋和 r 蛋白的相互依赖性，详细说明了这些元件的结合和对接是如何紧密耦合的。这些结果对我们理解核糖体生物发生的质量控制机制具有广泛的意义，并展示了 cryo-EM 中的异质性分析在揭示生物系统中功能相关信息方面的强大功能。
