Conserved motifs in nuclear genes encoding predicted mitochondrial proteins in Trypanosoma cruzi

Trypanosoma cruzi, the protozoan parasite that causes Chagas’ disease, exhibits peculiar biological features. Among them, the presence of a unique mitochondrion is remarkable. Even though the mitochondrial DNA constitutes up to 25% of total cellular DNA, the structure and functionality of the mitochondrion are dependent on the expression of the nuclear genome. As in other eukaryotes, specific peptide signals have been proposed to drive the mitochondrial localization of a subset of trypanosomatid proteins. However, there are mitochondrial proteins encoded in the nuclear genome that lack of a peptide signal. In other eukaryotes, alternative protein targeting to subcellular organelles via mRNA localization has also been recognized and specific mRNA localization towards the mitochondria has been described. With the aim of seeking for mitochondrial localization signals in T. cruzi, we developed a strategy to build a comprehensive database of nuclear genes encoding predicted mitochondrial proteins (MiNT) in the TriTryps (T. cruzi, T. brucei and L. major). We found that approximately 15% of their nuclear genome encodes mitochondrial products. In T. cruzi the MiNT database reaches 1438 genes and a conserved peptide signal, M(L/F) R (R/S) SS, named TryM-TaPe is found in 60% of these genes, suggesting that the canonical mRNA guidance mechanism is present. In addition, the search for compositional signals in the transcripts of T. cruzi MiNT genes produce a list, being worth to note a conserved non-translated element represented by the consensus sequence DARRVSG. Taking into account its reported interaction with the T. brucei TRRM3 protein which is enriched in the mitochondrial membrane fraction, we here suggest a putative zip code role for this element. Globally, here we provide an inventory of the mitochondrial proteins in T. cruzi and give evidence for the existence of both peptide and mRNA signals specific to nuclear encoded mitochondrial proteins.克氏锥虫（Trypanosoma cruzi）是引发恰加斯病（Chagas’ disease）的原生动物寄生虫，具备独特的生物学特性。其中，其独特的线粒体（mitochondrion）结构尤为引人注目。尽管线粒体DNA（mitochondrial DNA）可占细胞总DNA的25%之多，但线粒体的结构与功能仍依赖于核基因组的表达。与其他真核生物（eukaryotes）类似，已有研究提出特定的肽信号（peptide signal）可驱动锥虫类（trypanosomatid）蛋白质子集定位于线粒体。然而，也存在一类由核基因组编码、却缺乏肽信号的线粒体蛋白。在其他真核生物中，通过mRNA定位（mRNA localization）实现蛋白质靶向亚细胞细胞器的机制也已被证实，且已有针对线粒体的特异性mRNA定位的相关报道。 为探寻克氏锥虫（Trypanosoma cruzi）的线粒体定位信号，我们开发了一套研究策略，用于构建TriTryps（克氏锥虫、布氏锥虫T. brucei和利什曼原虫L. major）中编码预测线粒体蛋白的核基因综合数据库（MiNT）。研究发现，这三个物种的核基因组中约有15%编码线粒体相关产物。在克氏锥虫中，MiNT数据库涵盖1438个基因，其中60%的基因含有保守肽信号M(L/F)R(R/S)SS，我们将其命名为TryM-TaPe，这表明经典的mRNA引导机制确实存在。此外，对克氏锥虫MiNT基因转录本的组成信号进行检索后得到一组序列，其中值得关注的是一段以共有序列DARRVSG为代表的保守非翻译元件。结合已有研究报道该元件与布氏锥虫TRRM3蛋白（富集于线粒体膜组分）存在相互作用，我们在此提出该元件可能发挥邮政编码样的定位功能。 总体而言，本研究完成了克氏锥虫线粒体蛋白的系统编目，并为核编码线粒体蛋白所特有的肽信号与mRNA信号的共同存在提供了实验证据。