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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >A novel precursor recognition element facilitates posttranslational binding to the signal recognition particle in chloroplasts
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A novel precursor recognition element facilitates posttranslational binding to the signal recognition particle in chloroplasts

机译：新型前体识别元件可促进翻译后与叶绿体中信号识别颗粒的结合

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摘要

Signal recognition particles (SRPs) in the cytosols of prokaryotes and eukaryotes are used to target proteins to cytoplasmic membranes and the endoplasmic reticulum. respectively. The mechanism of targeting relies on cotranslational SRP binding to hydrophobic signal sequences. An organellar SRP identified in chloroplasts (cpSRP) is unusual in that it functions posttranslation- ally to localize a subset of nuclear-encoded thylakoid proteins. In assays that reconstitute thylakoid integration of the light harvest- ing chlorophyll-binding protein (LHCP), stromal cpSRP binds LHCP posttranslationally to form a cpSRP/LHCP transit complex. which is believed to represent the LHCP form targeted to thylakoids. In this investigation, we have identified an 18-aa sequence motif in LHCP (L18) that. along with a hydrophobic domain. is required for transit 'complex formation. Fusion of L18 to the amino terminus of an endoplasmic reticulum-targeted protein, preprolactin, Led to tran- sit complex formation whereas wild-type preprolactin exhibited no ability to form a transit complex. In addition, a synthetic L18 peptide. which competed with LHCP for transit complex formation, caused a parallel inhibition of LHCP integration. Translocation of proteins by the thylakoid Sec and Delta pH transport systems was unaffected by the highest concentration of L18 peptide ex- amined. Our data indicate that a motif contained in L18 functions in precursor recruitment to the posttranslational SRP pathway, one of at least four different thylakoid sorting pathways used by chloroplasts.
机译：原核生物和真核生物的细胞质中的信号识别颗粒（SRP）用于将蛋白质靶向细胞质膜和内质网。分别。靶向机制依赖于共翻译SRP与疏水信号序列的结合。叶绿体（cpSRP）中鉴定出的一种细胞器SRP是不寻常的，因为它在翻译后起作用以定位核编码类囊体蛋白的一个子集。在重新构建光收集叶绿素结合蛋白（LHCP）类囊体整合的测定中，基质cpSRP在翻译后与LHCP结合形成cpSRP / LHCP转运复合体。据信它代表针对类囊体的LHCP形式。在这项研究中，我们确定了LHCP（L18）中的18-aa序列基序。以及疏水域。是运输“复杂地带”所必需的。 L18融合到内质网靶向蛋白，泌乳素原的氨基末端，导致转运复合物的形成，而野生型泌乳素则没有形成转运复合物的能力。另外，合成的L18肽。与LHCP竞争转运复合物的形成，导致LHCP整合的平行抑制。通过类囊体Sec和Delta pH转运系统转运的蛋白质不受最高浓度的L18肽检查的影响。我们的数据表明，L18中包含的基序在翻译前SRP途径（叶绿体使用的至少四种不同类囊体分类途径之一）的前体募集中起作用。

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