Singha Ujjal K, Peprah Emmanuel, Williams Shuntae, Walker Robert, Saha Lipi, Chaudhuri Minu
Department of Microbial Pathogenesis and Immune Response, Meharry Medical College, Nashville, TN 37208, USA.
Mol Biochem Parasitol. 2008 May;159(1):30-43. doi: 10.1016/j.molbiopara.2008.01.003. Epub 2008 Feb 3.
Mitochondrial protein translocation machinery in the kinetoplastid parasites, like Trypanosoma brucei, has been characterized poorly. In T. brucei genome database, one homolog for a protein translocator of mitochondrial inner membrane (Tim) has been found, which is closely related to Tim17 from other species. The T. brucei Tim17 (TbTim17) has a molecular mass 16.2kDa and it possesses four characteristic transmembrane domains. The protein is localized in the mitochondrial inner membrane. The level of TbTim17 protein is 6-7-fold higher in the procyclic form that has a fully active mitochondrion, than in the mammalian bloodstream form of T. brucei, where many of the mitochondrial activities are suppressed. Knockdown of TbTim17 expression by RNAi caused a cessation of cell growth in the procyclic form and reduced growth rate in the bloodstream form. Depletion of TbTim17 decreased mitochondrial membrane potential more in the procyclic than bloodstream form. However, TbTim17 knockdown reduced the expression level of several nuclear encoded mitochondrial proteins in both the forms. Furthermore, import of presequence containing nuclear encoded mitochondrial proteins was significantly reduced in TbTim17 depleted mitochondria of the procyclic as well as the bloodstream form, confirming that TbTim17 is critical for mitochondrial protein import in both developmental forms. Together, these show that TbTim17 is the translocator of nuclear encoded mitochondrial proteins and its expression is regulated according to mitochondrial activities in T. brucei.
在锥虫等动基体寄生虫中，线粒体蛋白质转运机制的特征了解甚少。在布氏锥虫基因组数据库中，发现了一个线粒体内膜蛋白质转运体（Tim）的同源物，它与其他物种的Tim17密切相关。布氏锥虫Tim17（TbTim17）分子量为16.2kDa，具有四个特征性跨膜结构域。该蛋白质定位于线粒体内膜。在具有完全活跃线粒体的前循环形式中，TbTim17蛋白水平比布氏锥虫的哺乳动物血流形式高6 - 7倍，在后者中许多线粒体活动受到抑制。通过RNA干扰敲低TbTim17的表达导致前循环形式的细胞生长停止，血流形式的生长速率降低。与血流形式相比，TbTim17的缺失在前循环形式中使线粒体膜电位下降更多。然而，敲低TbTim17在两种形式中均降低了几种核编码线粒体蛋白的表达水平。此外，在前循环形式和血流形式的TbTim17缺失的线粒体中，含前导序列的核编码线粒体蛋白的导入显著减少，证实TbTim17对于两种发育形式中的线粒体蛋白导入至关重要。总之，这些结果表明TbTim17是核编码线粒体蛋白的转运体，其表达在布氏锥虫中根据线粒体活动受到调控。
