Distinct Pathways Mediate the Sorting of Tail-Anchored Proteins to the Plastid Outer Envelope
Distinct Pathways Mediate the Sorting of Tail-Anchored Proteins to the Plastid Outer Envelope
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DOI：
10.1371/journal.pone.0010098
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发表时间：
2010-04-14
期刊：
影响因子：
3.7
通讯作者：
Mullen, Robert T.
中科院分区：
文献类型：
--
作者：
Dhanoa, Preetinder K.;Richardson, Lynn G. L.;Mullen, Robert T.
背景资料：尾锚定蛋白（Tail-anchored protein，TA）是一类独特的膜蛋白，在细胞内具有重要的功能，包括氧化还原反应、囊泡运输和蛋白质转运等。虽然负责将TA蛋白分选到酵母和哺乳动物中正确的细胞内目的地的分子靶向信号和途径已经开始被表征，但是关于TA蛋白在植物细胞中的生物合成，特别是对于那些分选到质体外被膜的生物合成，所知相对较少。在这里，我们研究了三种质体TA蛋白的生物发生，包括位于叶绿体外被膜的转位子的33-kDa和34-kDa GTP酶（Toc 33和Toc 34）和一种新的9-kDa蛋白的未知功能，我们在这里定义为外包膜TA蛋白（OEP 9）。使用体内和体外试验的组合，我们表明，OEP 9利用不同的分选途径比Toc 33和Toc 34使用。例如，虽然所有三种TA蛋白与胞质OEP伴侣/受体AKR 2A相互作用，但OEP 9内的质体靶向信息与Toc 33和Toc 34内的质体靶向信息不同。Toc 33和Toc 34似乎也不同于OEP 9，因为它们的插入依赖于它们自身和质体外被膜的独特脂质组成。相比之下，OEP 9插入质体外被膜中以蛋白质依赖性方式发生，但不依赖于Toc 33/34，膜脂质似乎主要用于促进该TA蛋白的正常热力学整合。总的来说，这些结果提供了支持质体TA外被膜蛋白至少有两种分选途径的证据，不仅阐明了复杂多样性，除了涉及蛋白质靶向和插入质体的途径外，还包括一般而言将TA蛋白递送至其适当细胞内位置的分子机制。
Background: Tail-anchored (TA) proteins are a distinct class of membrane proteins that are sorted post-translationally to various organelles and function in a number of important cellular processes, including redox reactions, vesicular trafficking and protein translocation. While the molecular targeting signals and pathways responsible for sorting TA proteins to their correct intracellular destinations in yeasts and mammals have begun to be characterized, relatively little is known about TA protein biogenesis in plant cells, especially for those sorted to the plastid outer envelope.Methodology/Principal Findings: Here we investigated the biogenesis of three plastid TA proteins, including the 33-kDa and 34-kDa GTPases of the translocon at the outer envelope of chloroplasts (Toc33 and Toc34) and a novel 9-kDa protein of unknown function that we define here as an outer envelope TA protein (OEP9). Using a combination of in vivo and in vitro assays we show that OEP9 utilizes a different sorting pathway than that used by Toc33 and Toc34. For instance, while all three TA proteins interact with the cytosolic OEP chaperone/receptor, AKR2A, the plastid targeting information within OEP9 is distinct from that within Toc33 and Toc34. Toc33 and Toc34 also appear to differ from OEP9 in that their insertion is dependent on themselves and the unique lipid composition of the plastid outer envelope. By contrast, the insertion of OEP9 into the plastid outer envelope occurs in a proteinaceous-dependent, but Toc33/34-independent manner and membrane lipids appear to serve primarily to facilitate normal thermodynamic integration of this TA protein.Conclusions/Significance: Collectively, the results provide evidence in support of at least two sorting pathways for plastid TA outer envelope proteins and shed light on not only the complex diversity of pathways involved in the targeting and insertion of proteins into plastids, but also the molecular mechanisms that underlie the delivery of TA proteins to their proper intracellular locations in general.