Coexpressed subunits of dual genetic origin define a conserved supercomplex mediating essential protein import into chloroplasts.
Coexpressed subunits of dual genetic origin define a conserved supercomplex mediating essential protein import into chloroplasts.
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DOI：
10.1073/pnas.2014294117
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发表时间：
2020-12-22
影响因子：
11.1
通讯作者：
Walter P
中科院分区：
文献类型：
--
作者：
Ramundo S;Asakura Y;Salomé PA;Strenkert D;Boone M;Mackinder LCM;Takafuji K;Dinc E;Rahire M;Crèvecoeur M;Magneschi L;Schaad O;Hippler M;Jonikas MC;Merchant S;Nakai M;Rochaix JD;Walter P
叶绿体在真核生物的光合作用中起着至关重要的作用。就像线粒体一样，它们也包含自己的基因组。然而，大多数叶绿体蛋白是由核基因编码的，在细胞质中翻译，必须穿过叶绿体被膜才能到达细胞器内的适当目的地。尽管它的基本作用，我们对催化叶绿体蛋白输入的机制的了解是不完整的，也是有争议的。在这里，我们以绿藻衣藻为模型系统，研究叶绿体蛋白输入机制的进化保守性、组成和功能。我们的发现有助于澄清目前关于叶绿体蛋白输入机制的组成的争论，为其生物发生的跨区间协调提供证据，并为其结构表征开辟有希望的途径。在光合作用的真核生物中，数以千计的蛋白质在细胞质中被翻译，并通过分别位于叶绿体被膜外膜和内膜上的两个转运子TOC和TIC的协同作用输入到叶绿体中。TOC和TIC复合体的分子组成在系统发育距离上的保守程度仍然存在争议。在这里，我们结合转录、生化和遗传工具在绿藻衣藻(Chlamydomonas Reinhardtii)中证明，尽管其一些成分缺乏明显的序列保守性，但藻类TIC复合体反映了拟南芥TIC复合体的分子组成。衣藻TIC复合体包含三个核编码亚基Tic20、Tic56和Tic100，以及一个叶绿体编码亚基Tic214，并与TOC复合体以及一些未鉴定的蛋白质相互作用形成稳定的超复合体(TIC-TOC)，表明蛋白质跨两种被膜的输入是机械耦合的。编码已知和未知TIC-TOC组分的核基因和叶绿体基因的表达是高度协调的，这表明必须存在一种跨间隔边界调节其生物发生的机制。Tic214是TIC-TOC复合体中唯一的叶绿体编码亚基，条件性抑制Tic214影响叶绿体蛋白质的输入，在叶绿体核糖体生物发生和蛋白质折叠中起重要作用，并诱导一种多效性胁迫反应，包括参与叶绿体未折叠蛋白反应的几种蛋白质。这些发现强调了TIC-TOC超复合体在维持叶绿体蛋白平衡方面的功能重要性。
Chloroplasts are of vital importance in photosynthetic eukaryotic organisms. Like mitochondria, they contain their own genomes. Nevertheless, most chloroplast proteins are encoded by nuclear genes, translated in the cytosol, and must cross the chloroplast envelope membranes to reach their proper destinations inside the organelle. Despite its fundamental role, our knowledge of the machinery catalyzing chloroplast protein import is incomplete and controversial. Here, we address the evolutionary conservation, composition, and function of the chloroplast protein import machinery using the green alga Chlamydomonas reinhardtii as a model system. Our findings help clarify the current debate regarding the composition of the chloroplast protein import machinery, provide evidence for cross-compartmental coordination of its biogenesis, and open promising avenues for its structural characterization. In photosynthetic eukaryotes, thousands of proteins are translated in the cytosol and imported into the chloroplast through the concerted action of two translocons—termed TOC and TIC—located in the outer and inner membranes of the chloroplast envelope, respectively. The degree to which the molecular composition of the TOC and TIC complexes is conserved over phylogenetic distances has remained controversial. Here, we combine transcriptomic, biochemical, and genetic tools in the green alga Chlamydomonas (Chlamydomonas reinhardtii) to demonstrate that, despite a lack of evident sequence conservation for some of its components, the algal TIC complex mirrors the molecular composition of a TIC complex from Arabidopsis thaliana. The Chlamydomonas TIC complex contains three nuclear-encoded subunits, Tic20, Tic56, and Tic100, and one chloroplast-encoded subunit, Tic214, and interacts with the TOC complex, as well as with several uncharacterized proteins to form a stable supercomplex (TIC-TOC), indicating that protein import across both envelope membranes is mechanistically coupled. Expression of the nuclear and chloroplast genes encoding both known and uncharacterized TIC-TOC components is highly coordinated, suggesting that a mechanism for regulating its biogenesis across compartmental boundaries must exist. Conditional repression of Tic214, the only chloroplast-encoded subunit in the TIC-TOC complex, impairs the import of chloroplast proteins with essential roles in chloroplast ribosome biogenesis and protein folding and induces a pleiotropic stress response, including several proteins involved in the chloroplast unfolded protein response. These findings underscore the functional importance of the TIC-TOC supercomplex in maintaining chloroplast proteostasis.
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影响因子：
4.9
作者：
Aoki Y;Okamura Y;Ohta H;Kinoshita K;Obayashi T
通讯作者：
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DOI：
10.1083/jcb.136.5.983
发表时间：
1997-03-10
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The Journal of cell biology
影响因子：
--
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影响因子：
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作者：
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通讯作者：
Goodenough, U W
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DOI：
10.1111/tpj.13788
发表时间：
2018-03
期刊：
The Plant journal : for cell and molecular biology
影响因子：
--
作者：
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通讯作者：
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影响因子：
7.2
作者：
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