The prokaryotic translation elongation factor P (EF-P) and the eukaryotic/archaeal counterparts eIF5A/aIF5A are proteins that serve a crucial role in mitigating ribosomal stalling during the translation of specific sequences, notably those containing consecutive proline residues (1,2). Although mitochondrial DNA-encoded proteins synthesized by mitochondrial ribosomes also contain polyproline stretches, an EF-P/eIF5A mitochondrial counterpart remains unidentified. Here, we show that the missing factor is TACO1, a protein causative of a juvenile form of neurodegenerative Leigh's syndrome associated with cytochrome c oxidase deficiency, until now believed to be a translational activator of COX1 mRNA. By using a combination of metabolic labeling, puromycin release and mitoribosome profiling experiments, we show that TACO1 is required for the rapid synthesis of the polyproline-rich COX1 and COX3 cytochrome c oxidase subunits, while its requirement is negligible for other mitochondrial DNA-encoded proteins. In agreement with a role in translation efficiency regulation, we show that TACO1 cooperates with the N-terminal extension of the large ribosomal subunit bL27m to provide stability to the peptidyl-transferase center during elongation. This study illuminates the translation elongation dynamics within human mitochondria, a TACO1-mediated biological mechanism in place to mitigate mitoribosome stalling at polyproline stretches during protein synthesis, and the pathological implications of its malfunction.

中文翻译：

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人类线粒体翻译因子 TACO1 缓解线粒体糖体在聚脯氨酸延伸处的停滞


原核翻译延伸因子 P (EF-P) 和真核/古细菌对应物 eIF5A/aIF5A 是在特定序列（特别是含有连续脯氨酸残基的序列）翻译过程中在减轻核糖体停滞中发挥关键作用的蛋白质 (1,2)。尽管由线粒体核糖体合成的线粒体 DNA 编码蛋白也含有聚脯氨酸片段，但 EF-P/eIF5A 线粒体对应物仍未鉴定。在这里，我们发现缺失的因子是 TACO1，这是一种与细胞色素 C 氧化酶缺乏相关的青少年神经退行性利氏综合征的致病蛋白，迄今为止被认为是 COX1 mRNA 的翻译激活剂。通过结合代谢标记、嘌呤霉素释放和线粒体分析实验，我们发现 TACO1 是快速合成富含聚脯氨酸的 COX1 和 COX3 细胞色素 C 氧化酶亚基所必需的，而对于其他线粒体 DNA 编码蛋白来说，其需求量可以忽略不计。与翻译效率调节中的作用一致，我们表明 TACO1 与大核糖体亚基 bL27m 的 N 端延伸配合，在延伸过程中为肽基转移酶中心提供稳定性。这项研究阐明了人类线粒体内的翻译伸长动力学、一种 TACO1 介导的生物机制，用于减轻蛋白质合成过程中线粒体糖体在聚脯氨酸拉伸处的停滞，以及其功能障碍的病理学意义。