Department of Chemistry, Indiana University, Bloomington, Indiana 47405.
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125.
J Biol Chem. 2020 May 15;295(20):6798-6808. doi: 10.1074/jbc.RA120.012706. Epub 2020 Mar 13.
Viruses maximize their genetic coding capacity through a variety of biochemical mechanisms, including programmed ribosomal frameshifting (PRF), which facilitates the production of multiple proteins from a single mRNA transcript. PRF is typically stimulated by structural elements within the mRNA that generate mechanical tension between the transcript and ribosome. However, in this work, we show that the forces generated by the cotranslational folding of the nascent polypeptide chain can also enhance PRF. Using an array of biochemical, cellular, and computational techniques, we first demonstrate that the Sindbis virus structural polyprotein forms two competing topological isomers during its biosynthesis at the ribosome-translocon complex. We then show that the formation of one of these topological isomers is linked to PRF. Coarse-grained molecular dynamics simulations reveal that the translocon-mediated membrane integration of a transmembrane domain upstream from the ribosomal slip site generates a force on the nascent polypeptide chain that scales with observed frameshifting. Together, our results indicate that cotranslational folding of this viral protein generates a tension that stimulates PRF. To our knowledge, this constitutes the first example in which the conformational state of the nascent polypeptide chain has been linked to PRF. These findings raise the possibility that, in addition to RNA-mediated translational recoding, a variety of cotranslational folding or binding events may also stimulate PRF.
病毒通过多种生化机制最大限度地提高其遗传编码能力，包括核糖体框架移位（PRF），这有助于从单个 mRNA 转录本中产生多种蛋白质。PRF 通常由 mRNA 中的结构元件刺激，这些结构元件在转录本和核糖体之间产生机械张力。然而，在这项工作中，我们表明新生多肽链的共翻译折叠产生的力也可以增强 PRF。我们使用一系列生化、细胞和计算技术，首先证明在核糖体-易位复合物中合成时，辛德毕斯病毒结构多蛋白形成两种竞争的拓扑异构体。然后，我们表明其中一种拓扑异构体的形成与 PRF 相关。粗粒度分子动力学模拟表明，跨膜结构域在核糖体滑位上游的易位介导的膜整合会在新生多肽链上产生与观察到的移框相关的力。总之，我们的结果表明，这种病毒蛋白的共翻译折叠会产生张力，从而刺激 PRF。据我们所知，这是首次将新生多肽链的构象状态与 PRF 联系起来的例子。这些发现提出了一种可能性，即除了 RNA 介导的翻译重编码外，各种共翻译折叠或结合事件也可能刺激 PRF。
