The Trypanosome Exocyst: A Conserved Structure Revealing a New Role in Endocytosis.
The Trypanosome Exocyst: A Conserved Structure Revealing a New Role in Endocytosis.
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锥虫胞外囊肿：一种保守的结构，揭示了内吞作用的新作用。
DOI：
10.1371/journal.ppat.1006063
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发表时间：
2017-01
期刊：
影响因子：
6.7
通讯作者：
Field MC
中科院分区：
文献类型：
--
作者：
Boehm CM;Obado S;Gadelha C;Kaupisch A;Manna PT;Gould GW;Munson M;Chait BT;Rout MP;Field MC
膜转运是大多数感染性生物发病机制的重要组成部分。在非洲锥虫中，进出质膜的运输与免疫逃避和抗原变异密切相关。在哺乳动物和真菌中，八聚体胞囊复合体介导胞吐的后期步骤，但比较基因组学表明锥虫只保留了六个典型亚基，这意味着机制上的差异。我们通过亲和分离直接确定了布氏锥虫胞囊的组成，并证明该寄生虫复合体是非美聚的，保留了所有8个标准亚基（尽管在序列水平上高度分化）和一个新的基本亚基，Exo99。Exo99和Sec15基因敲低在活力、形态和转运途径方面具有显著相似的表型。值得注意的是，Sec15和Exo99在胞吞作用中都有明确的功能，整体蛋白质组学分析表明Sec15和Exo99在维持表面蛋白质组中起重要作用。综上所述，这些数据表明锥虫体内还有其他囊泡功能，可能包括内吞作用、再循环和控制表面成分。HeLa细胞的敲低表明其在内吞作用中的作用与后生动物细胞相同。我们的结论是，虽然锥虫胞囊具有新的成分，但整体功能似乎是保守的，并建议独特的亚基可能提供治疗机会。贩运是大多数真核细胞的一个重要过程，并已适应特定物种以适应其需求。有很好的证据表明，就内吞和胞外途径中功能的谱系特异性蛋白质的进化而言，植物和动物的新途径和机制的创新，以及新兴的数据表明，类似的新特征也存在于单细胞原生动物中。这表明在膜运输中可能存在显著的变异。在这里，我们已经确定了一种新的外囊成分，一种在蛋白质分泌后期很重要的复合物。此外，我们还发现有证据表明，囊泡参与内吞作用，扩大了该复合物的功能范围。
Membrane transport is an essential component of pathogenesis for most infectious organisms. In African trypanosomes, transport to and from the plasma membrane is closely coupled to immune evasion and antigenic variation. In mammals and fungi an octameric exocyst complex mediates late steps in exocytosis, but comparative genomics suggested that trypanosomes retain only six canonical subunits, implying mechanistic divergence. We directly determined the composition of the Trypanosoma brucei exocyst by affinity isolation and demonstrate that the parasite complex is nonameric, retaining all eight canonical subunits (albeit highly divergent at the sequence level) plus a novel essential subunit, Exo99. Exo99 and Sec15 knockdowns have remarkably similar phenotypes in terms of viability and impact on morphology and trafficking pathways. Significantly, both Sec15 and Exo99 have a clear function in endocytosis, and global proteomic analysis indicates an important role in maintaining the surface proteome. Taken together these data indicate additional exocyst functions in trypanosomes, which likely include endocytosis, recycling and control of surface composition. Knockdowns in HeLa cells suggest that the role in endocytosis is shared with metazoan cells. We conclude that, whilst the trypanosome exocyst has novel components, overall functionality appears conserved, and suggest that the unique subunit may provide therapeutic opportunities. Trafficking is an important process in most eukaryotic cells, and has been adapted for specific species to accommodate their requirements. There is good evidence for the innovation of novel routes and mechanisms in plants and animals in terms of the evolution of lineage-specific proteins that function within the endocytic and exocytic pathways, and emerging data indicates that similar novel features are also present in unicellular protozoa. This suggests the likely presence of significant variation within membrane trafficking. Here we have identified a novel component of the exocyst, a complex that is important in late stages of protein secretion. Moreover, we also find evidence that the exocyst is involved in endocytosis extending the functional reach of this complex.