Chang Ya-Ting, Barad Benjamin A, Hamid Juliette, Rahmani Hamidreza, Zid Brian M, Grotjahn Danielle A
Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, USA.
Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR, USA.
J Cell Biol. 2025 Apr 7;224(4). doi: 10.1083/jcb.202407110. Epub 2025 Mar 6.
Most of the mitochondria proteome is nuclear-encoded, synthesized by cytoplasmic ribosomes, and targeted to the mitochondria posttranslationally. However, a subset of mitochondrial-targeted proteins is imported co-translationally, although the molecular mechanisms governing this process remain unclear. We employ cellular cryo-electron tomography to visualize interactions between cytoplasmic ribosomes and mitochondria in Saccharomyces cerevisiae. We use surface morphometrics tools to identify a subset of ribosomes optimally oriented on mitochondrial membranes for protein import. This allows us to establish the first subtomogram average structure of a cytoplasmic ribosome at the mitochondrial surface in the native cellular context, which showed three distinct connections with the outer mitochondrial membrane surrounding the peptide exit tunnel. Further, this analysis demonstrated that cytoplasmic ribosomes primed for mitochondrial protein import cluster on the outer mitochondrial membrane at sites of local constrictions of the outer and inner mitochondrial membranes. Overall, our study reveals the architecture and the spatial organization of cytoplasmic ribosomes at the mitochondrial surface, providing a native cellular context to define the mechanisms that mediate efficient mitochondrial co-translational protein import.
大多数线粒体蛋白质组是由核基因编码的，由细胞质核糖体合成，并在翻译后靶向输送到线粒体。然而，尽管控制这一过程的分子机制尚不清楚，但仍有一部分靶向线粒体的蛋白质是在翻译过程中被导入的。我们利用细胞冷冻电子断层扫描技术来观察酿酒酵母中细胞质核糖体与线粒体之间的相互作用。我们使用表面形态计量学工具来识别一组在线粒体外膜上具有最佳定向以进行蛋白质导入的核糖体。这使我们能够在天然细胞环境中建立线粒体表面细胞质核糖体的首个亚断层平均结构，该结构显示与围绕肽出口通道的线粒体外膜有三种不同的连接。此外，该分析表明，准备进行线粒体蛋白质导入的细胞质核糖体聚集在线粒体外膜上内外膜局部收缩的部位。总体而言，我们的研究揭示了线粒体表面细胞质核糖体的结构和空间组织，为定义介导高效线粒体共翻译蛋白质导入的机制提供了天然细胞环境。
