Department of Biochemistry and Molecular Biology, Monash University, Clayton Campus, Melbourne, Victoria, Australia.
PLoS Pathog. 2010 Mar 19;6(3):e1000812. doi: 10.1371/journal.ppat.1000812.
Several essential biochemical processes are situated in mitochondria. The metabolic transformation of mitochondria in distinct lineages of eukaryotes created proteomes ranging from thousands of proteins to what appear to be a much simpler scenario. In the case of Entamoeba histolytica, tiny mitochondria known as mitosomes have undergone extreme reduction. Only recently a single complete metabolic pathway of sulfate activation has been identified in these organelles. The E. histolytica mitosomes do not produce ATP needed for the sulfate activation pathway and for three molecular chaperones, Cpn60, Cpn10 and mtHsp70. The already characterized ADP/ATP carrier would thus be essential to provide cytosolic ATP for these processes, but how the equilibrium of inorganic phosphate could be maintained was unknown. Finally, how the mitosomal proteins are translocated to the mitosomes had remained unclear. We used a hidden Markov model (HMM) based search of the E. histolytica genome sequence to discover candidate (i) mitosomal phosphate carrier complementing the activity of the ADP/ATP carrier and (ii) membrane-located components of the protein import machinery that includes the outer membrane translocation channel Tom40 and membrane assembly protein Sam50. Using in vitro and in vivo systems we show that E. histolytica contains a minimalist set up of the core import components in order to accommodate a handful of mitosomal proteins. The anaerobic and parasitic lifestyle of E. histolytica has produced one of the simplest known mitochondrial compartments of all eukaryotes. Comparisons with mitochondria of another amoeba, Dictystelium discoideum, emphasize just how dramatic the reduction of the protein import apparatus was after the loss of archetypal mitochondrial functions in the mitosomes of E. histolytica.
几种重要的生化过程位于线粒体中。不同真核生物谱系中线粒体的代谢转化创造了蛋白质组，从数千种蛋白质到似乎更简单的情况都有。在溶组织内阿米巴中，被称为线粒体体的微小线粒体经历了极端的减少。直到最近，才在这些细胞器中鉴定出单个完整的硫酸盐激活代谢途径。溶组织内阿米巴的线粒体体不能产生硫酸盐激活途径和三种分子伴侣 Cpn60、Cpn10 和 mtHsp70 所需的 ATP。已经表征的 ADP/ATP 载体因此对于为这些过程提供细胞质 ATP 是必不可少的，但是如何维持无机磷酸盐的平衡是未知的。最后，线粒体蛋白如何易位到线粒体体仍然不清楚。我们使用基于隐马尔可夫模型 (HMM) 的搜索对溶组织内阿米巴基因组序列进行搜索，以发现候选物 (i) 线粒体磷酸盐载体补充 ADP/ATP 载体的活性，和 (ii) 蛋白质导入机制的膜定位组件，包括外膜转运通道 Tom40 和膜组装蛋白 Sam50。我们使用体外和体内系统表明，溶组织内阿米巴含有一组最小的核心导入组件，以容纳少数几种线粒体体蛋白。溶组织内阿米巴的厌氧和寄生生活方式产生了所有真核生物中最简单的已知线粒体隔间之一。与另一种变形虫 Dictystelium discoideum 的线粒体进行比较，强调了在溶组织内阿米巴的线粒体体中失去典型的线粒体功能后，蛋白质导入装置的减少是多么显著。
