Mitochondrial protein import depends on heterooligomeric translocases in the outer and inner membranes. Using import substrates consisting of various lengths of the N-terminal part of mitochondrial dihydrolipoamide dehydrogenase (LDH) fused to dihydrofolate reductase we present an in vivo analysis showing that in Trypanosoma brucei at least 96 aa of mature LDH are required to efficiently produce an import intermediate that spans both translocases. This is different to yeast, where around 50 aa are sufficient to achieve the same task and likely reflects the different arrangement and architecture of the trypanosomal mitochondrial translocases. Furthermore, we show that formation of the stuck import intermediate leads to a strong growth inhibition suggesting that, depending on the length of the LDH, the import channels in the translocases are quantitatively blocked.

线粒体蛋白的输入取决于外膜和内膜中的异源寡聚转位酶。使用由与二氢叶酸还原酶融合的线粒体二氢硫辛酰胺脱氢酶 (LDH) 的不同长度 N 末端部分组成的导入底物，我们提出了一项体内分析，表明在布氏锥虫中至少需要 96 aa 的成熟 LDH 才能有效地生产跨越两个易位酶的导入中间体。这与酵母不同，其中大约 50 个氨基酸足以完成相同的任务，并且可能反映了锥虫线粒体转位酶的不同排列和结构。此外，我们表明卡住的进口中间体的形成导致强烈的生长抑制，这表明，根据 LDH 的长度，转位酶中的进口通道被定量阻断。