Chloroplast protein targeting involves localized translation in Chlamydomonas
Chloroplast protein targeting involves localized translation in Chlamydomonas
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DOI：
10.1073/pnas.0811268106
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发表时间：
2009-02-03
影响因子：
11.1
通讯作者：
Zerges, William
中科院分区：
文献类型：
--
作者：
Uniacke, James;Zerges, William
真核细胞的区间化要求新合成的蛋白质定位于它们所在的区室。在叶绿体中，几千种蛋白质参与光合作用、叶绿体基因组的表达和其他过程。大多数叶绿体蛋白是在细胞质中合成的，然后输入，然后靶向特定的叶绿体隔室。其余的由叶绿体基因组编码，在细胞器内合成，并以刚刚开始被阐明的机制为靶标。我们利用荧光共聚焦显微镜研究了几种叶绿体蛋白在绿藻衣藻中的靶向机制。这些蛋白质包括从细胞质输入的核酮糖二磷酸羧基酶小亚基(Rubisco)和捕光复合体II(LHCII)亚基，以及在叶绿体中合成的两种蛋白质：光系统II的D1亚基和Rubisco大亚基。我们确定了每种蛋白质的靶向是否涉及编码它的信使核糖核酸的局部翻译。在这种情况下，我们探索了靶向序列是在新生多肽中还是在mRNA中，分别基于定位是依赖于翻译还是非依赖于翻译。结果揭示了两个新的靶向LHCII亚基导入和Ruisco大亚基靶向蛋白核的例子。他们还展示了三种已知机制中的每一种的例子-翻译后、共翻译(信号识别颗粒介导)和基于mRNA的-靶向特定叶绿体蛋白。我们的发现有助于在生化水平上指导这些途径的探索。
The compartmentalization of eukaryotic cells requires that newly synthesized proteins be targeted to the compartments in which they function. In chloroplasts, a few thousand proteins function in photosynthesis, expression of the chloroplast genome, and other processes. Most chloroplast proteins are synthesized in the cytoplasm, imported, and then targeted to a specific chloroplast compartment. The remainder are encoded by the chloroplast genome, synthesized within the organelle, and targeted by mechanisms that are only beginning to be elucidated. We used fluorescence confocal microscopy to explore the targeting mechanisms used by several chloroplast proteins in the green alga Chlamydomonas. These include the small subunit of ribulose bisphosphate carboxylase (rubisco) and the light-harvesting complex II (LHCII) subunits, which are imported from the cytoplasm, and 2 proteins synthesized in the chloroplast: the D1 subunit of photosystem II and the rubisco large subunit. We determined whether the targeting of each protein involves localized translation of the mRNA that encodes it. When this was the case, we explored whether the targeting sequence was in the nascent polypeptide or in the mRNA, based on whether the localization was translation-dependent or -independent, respectively. The results reveal 2 novel examples of targeting by localized translation, in LHCII subunit import and the targeting of the rubisco large subunit to the pyrenoid. They also demonstrate examples of each of the three known mechanisms - posttranslational, cotranslational (signal recognition particle-mediated), and mRNA-based - in the targeting of specific chloroplast proteins. Our findings can help guide the exploration of these pathways at the biochemical level.