Autophagy-Related Protein ATG8 Has a Noncanonical Function for Apicoplast Inheritance in Toxoplasma gondii.
Autophagy-Related Protein ATG8 Has a Noncanonical Function for Apicoplast Inheritance in Toxoplasma gondii.
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DOI：
10.1128/mbio.01446-15
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发表时间：
2015-10-27
期刊：
影响因子：
6.4
通讯作者：
Besteiro S
中科院分区：
文献类型：
--
作者：
Lévêque MF;Berry L;Cipriano MJ;Nguyen HM;Striepen B;Besteiro S
自噬是真核生物中广泛保守的分解代谢过程，其允许通过溶酶体途径快速降解不需要的蛋白质和细胞器。这种机制涉及形成一种称为自噬体的双膜结构，它可以隔离待降解的细胞成分。为了协调这一过程，酵母和动物依赖于一组保守的自噬相关蛋白（ATG）。这些因素中的关键是ATG8，一种细胞质蛋白，在诱导自噬后被招募到新生的自噬体膜。弓形虫是一种潜在的危害人类的病原体，其中只有一个子集的ATG似乎是目前。虽然这种真核寄生虫似乎能够在营养饥饿等应激下产生自噬体，但经典自噬途径的完整功能和生物学相关性尚不清楚。有趣的是，在弓形虫中，在正常的细胞内生长条件下，ATG 8定位于顶质体。顶质体是由次生内共生作用形成的四层膜包围的非光合质体。使用超分辨率显微镜和生物化学技术，我们表明，TgATG8定位于最外层膜的这个细胞器。我们通过产生条件性敲低突变体研究了TgATG 8在顶质体的不寻常功能。TgATG 8的消耗导致细胞器的快速丧失和随后的细胞内复制缺陷，表明该蛋白质对于维持顶质体稳态以及速殖子阶段的存活是必不可少的。更准确地说，TgATG 8的损失导致异常分离的顶质体进入后代，因为损失的物理相互作用的细胞器与中心体。根据定义，自噬是一种分解代谢过程，导致真核细胞成分的消化和再循环。自噬的分子机制主要在模式生物如酵母中被确定，但在遗传学上遥远的顶复门寄生虫中仍然缺乏特征。我们发现了一个不寻常的功能，自噬相关蛋白ATG8在弓形虫：TgATG8是至关重要的寄生虫在其宿主细胞内的正常复制。TgATG 8似乎与分解代谢自噬过程无关，它与寄生虫所携带的非光合质体的外膜相关联，称为顶质体，在细胞分裂期间，它在中心体驱动的细胞器遗传中起着重要作用。这不仅揭示了一种自噬相关蛋白的意想不到的功能，而且还揭示了一种细胞器的分裂过程，这种细胞器对一组重要的人类和动物病原体至关重要。
Autophagy is a catabolic process widely conserved among eukaryotes that permits the rapid degradation of unwanted proteins and organelles through the lysosomal pathway. This mechanism involves the formation of a double-membrane structure called the autophagosome that sequesters cellular components to be degraded. To orchestrate this process, yeasts and animals rely on a conserved set of autophagy-related proteins (ATGs). Key among these factors is ATG8, a cytoplasmic protein that is recruited to nascent autophagosomal membranes upon the induction of autophagy. Toxoplasma gondii is a potentially harmful human pathogen in which only a subset of ATGs appears to be present. Although this eukaryotic parasite seems able to generate autophagosomes upon stresses such as nutrient starvation, the full functionality and biological relevance of a canonical autophagy pathway are as yet unclear. Intriguingly, in T. gondii, ATG8 localizes to the apicoplast under normal intracellular growth conditions. The apicoplast is a nonphotosynthetic plastid enclosed by four membranes resulting from a secondary endosymbiosis. Using superresolution microscopy and biochemical techniques, we show that TgATG8 localizes to the outermost membrane of this organelle. We investigated the unusual function of TgATG8 at the apicoplast by generating a conditional knockdown mutant. Depletion of TgATG8 led to rapid loss of the organelle and subsequent intracellular replication defects, indicating that the protein is essential for maintaining apicoplast homeostasis and thus for survival of the tachyzoite stage. More precisely, loss of TgATG8 led to abnormal segregation of the apicoplast into the progeny because of a loss of physical interactions of the organelle with the centrosomes. By definition, autophagy is a catabolic process that leads to the digestion and recycling of eukaryotic cellular components. The molecular machinery of autophagy was identified mainly in model organisms such as yeasts but remains poorly characterized in phylogenetically distant apicomplexan parasites. We have uncovered an unusual function for autophagy-related protein ATG8 in Toxoplasma gondii: TgATG8 is crucial for normal replication of the parasite inside its host cell. Seemingly unrelated to the catabolic autophagy process, TgATG8 associates with the outer membrane of the nonphotosynthetic plastid harbored by the parasite called the apicoplast, and there it plays an important role in the centrosome-driven inheritance of the organelle during cell division. This not only reveals an unexpected function for an autophagy-related protein but also sheds new light on the division process of an organelle that is vital to a group of important human and animal pathogens.