Crystal structures of the Arabidopsis thaliana organellar RNA editing factors MORF1 and MORF9.
Crystal structures of the Arabidopsis thaliana organellar RNA editing factors MORF1 and MORF9.
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DOI：
10.1093/nar/gkx099
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发表时间：
2017-05-05
影响因子：
14.9
通讯作者：
Weber G
中科院分区：
文献类型：
--
作者：
Haag S;Schindler M;Berndt L;Brennicke A;Takenaka M;Weber G
在开花植物质体和线粒体中，RNA编辑体催化的C - to - U RNA高效编辑需要多个细胞器RNA编辑因子（MORF/RIP）蛋白。MORF蛋白含有一个保守的残基延伸（MORF-box），形成同源和异聚体，并与选定的PPR （pentatricopeptide repeat）蛋白相互作用，这些蛋白识别每个编辑位点。MORF-box的分子功能仍然难以捉摸，因为它与已知结构域没有序列相似性。我们确定了拟南芥线粒体MORF1和叶绿体MORF9 MORF-box的结构，它们都采用了一种新的球状褶皱（MORF结构域）。我们的结构陈述了MORF域及其通过疏水界面的特定二聚化的范例模型。我们通过酵母双杂交研究和采用基于结构的突变体的拉下试验交叉验证了界面。我们发现MORF结构域与n端铁氧还蛋白样结构域（NFLD）具有结构相似性，该结构域在细菌4-硫脲嘧啶tRNA合成酶中赋予RNA底物定位，这意味着在RNA编辑过程中MORF蛋白与RNA直接接触。通过MORF1和MORF9结构，我们阐明了一个未知的折叠，证实了MORF相互作用的研究，验证了MORF通过基于结构的突变体多聚的机制，并为植物RNA编辑体的完整结构表征铺平了道路。
In flowering plant plastids and mitochondria, multiple organellar RNA editing factor (MORF/RIP) proteins are required at most sites for efficient C to U RNA editing catalyzed by the RNA editosome. MORF proteins harbor a conserved stretch of residues (MORF-box), form homo- and heteromers and interact with selected PPR (pentatricopeptide repeat) proteins, which recognize each editing site. The molecular function of the MORF-box remains elusive since it shares no sequence similarity with known domains. We determined structures of the A. thaliana mitochondrial MORF1 and chloroplast MORF9 MORF-boxes which both adopt a novel globular fold (MORF domain). Our structures state a paradigmatic model for MORF domains and their specific dimerization via a hydrophobic interface. We cross-validate the interface by yeast two-hybrid studies and pulldown assays employing structure-based mutants. We find a structural similarity of the MORF domain to an N-terminal ferredoxin-like domain (NFLD), which confers RNA substrate positioning in bacterial 4-thio-uracil tRNA synthetases, implying direct RNA contacts of MORF proteins during RNA editing. With the MORF1 and MORF9 structures we elucidate a yet unknown fold, corroborate MORF interaction studies, validate the mechanism of MORF multimerization by structure-based mutants and pave the way towards a complete structural characterization of the plant RNA editosome.