Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe-Universität, Frankfurt am Main, Hessen 60438, Germany.
Nucleic Acids Res. 2018 Nov 16;46(20):10917-10929. doi: 10.1093/nar/gky746.
Initiation of bacterial translation requires that the ribosome-binding site in mRNAs adopts single-stranded conformations. In Gram-negative bacteria the ribosomal protein S1 (rS1) is a key player in resolving of structured elements in mRNAs. However, the exact mechanism of how rS1 unfolds persistent secondary structures in the translation initiation region (TIR) is still unknown. Here, we show by NMR spectroscopy that Vibrio vulnificus rS1 displays a unique architecture of its mRNA-binding domains, where domains D3 and D4 provide the mRNA-binding platform and cover the nucleotide binding length of the full-length rS1. D5 significantly increases rS1's chaperone activity, although it displays structural heterogeneity both in isolation and in presence of the other domains, albeit to varying degrees. The heterogeneity is induced by the switch between the two equilibrium conformations and is triggered by an order-to-order transition of two mutually exclusive secondary structures (β-strand-to-α-helix) of the 'AERERI' sequence. The conformational switching is exploited for melting of structured 5'-UTR's, as the conformational heterogeneity of D5 can compensate the entropic penalty of complex formation. Our data thus provides a detailed understanding of the intricate coupling of protein and RNA folding dynamics enabling translation initiation of structured mRNAs.
起始细菌翻译需要 mRNA 中的核糖体结合位点采用单链构象。在革兰氏阴性菌中，核糖体蛋白 S1（rS1）是解析 mRNA 中结构元件的关键因素。然而，rS1 如何展开翻译起始区（TIR）中持续存在的二级结构的确切机制仍不清楚。在这里，我们通过 NMR 光谱表明，创伤弧菌 rS1 显示出其 mRNA 结合结构域的独特结构，其中结构域 D3 和 D4 提供了 mRNA 结合平台，并覆盖了全长 rS1 的核苷酸结合长度。结构域 D5 显著增加了 rS1 的伴侣活性，尽管它在分离状态和其他结构域存在时都表现出结构异质性，但程度不同。这种异质性是由两种平衡构象之间的转换以及“AERERI”序列的两个相互排斥的二级结构（β-链到α-螺旋）的顺序到顺序转变引发的。构象转换可用于熔化结构 5'-UTR，因为 D5 的构象异质性可以补偿复合物形成的熵罚。因此，我们的数据提供了对蛋白质和 RNA 折叠动力学复杂耦合的详细理解，从而实现了结构 mRNA 的翻译起始。
