Expanded repertoire of kinetoplast associated proteins and unique mitochondrial DNA arrangement of symbiont-bearing trypanosomatids

In trypanosomatids, the kinetoplast is the portion of the single mitochondrion that is connected to the basal body and contains the kDNA, a network composed by circular and interlocked DNA. The kDNA packing is conducted by Kinetoplast Associated Proteins (KAPs), which are similar to eukaryotic histone H1. In symbiont-harboring trypanosomatids (SHTs) such as Angomonas deanei and Strigomonas culicis, a ß-proteobacterium co-evolves with the host in a mutualistic relationship. The prokaryote confers nutritional benefits to the host and affects its cell structure. Atomic force microscopy showed that the topology of isolated kDNA networks is quite similar in the two SHT species. Ultrastructural analysis using high-resolution microscopy techniques revealed that the DNA fibrils are more compact in the kinetoplast region that faces the basal body and that the presence of the symbiotic bacterium does not interfere with kDNA topology. However, RT-PCR data revealed differences in the expression of KAPs in wild-type protozoa as compared to aposymbiotic cells. Immunolocalization showed that different KAPs present distinct distributions that are coincident in symbiont-bearing and in symbiont-free cells. Although KAP4 and KAP7 are shared by all trypanosomatid species, the expanded repertoire of KAPs in SHTs can be used as phylogenetic markers to distinguish different genera.在锥虫体生物中，动基体（kinetoplast）是单个线粒体的特化区域，与基体相连并包含动基体DNA（kDNA）——一种由环状互锁DNA构成的网络结构。动基体DNA的组装由动基体相关蛋白（Kinetoplast Associated Proteins, KAPs）介导，这类蛋白与真核生物组蛋白H1具有同源性。在携带共生体的锥虫体（symbiont-harboring trypanosomatids, SHTs）类群中，以迪恩安戈蒙滴虫（Angomonas deanei）和库氏斯特里戈蒙滴虫（Strigomonas culicis）为代表，一类β-变形菌与宿主形成互利共生的共进化关系。该原核生物可为宿主提供营养益处，并对宿主的细胞结构产生影响。原子力显微镜观测结果显示，两种SHT类群中分离得到的动基体DNA网络拓扑结构高度相似。采用高分辨率显微技术开展的超微结构分析显示，朝向基体的动基体区域内的DNA纤维丝更为紧凑，而共生细菌的存在并不会干扰动基体DNA的拓扑结构。然而，逆转录聚合酶链反应（RT-PCR）数据显示，与无共生体细胞相比，野生型原生动物的动基体相关蛋白表达存在差异。免疫定位实验结果表明，不同动基体相关蛋白具有独特的分布模式，且该模式在携带共生体与无共生体的细胞中保持一致。尽管KAP4与KAP7为所有锥虫体生物所共有，但SHT类群中扩增的动基体相关蛋白谱系可作为系统发育标记，用于区分不同的锥虫体属类群。