Molecular architecture of 40S translation initiation complexes on the hepatitis C virus IRES
Molecular architecture of 40S translation initiation complexes on the hepatitis C virus IRES
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DOI：
10.15252/embj.2022110581
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发表时间：
2022-07-13
期刊：
影响因子：
11.4
通讯作者：
Frank, Joachim
中科院分区：
文献类型：
--
作者：
Brown, Zuben P.;Abaeva, Irina S.;Frank, Joachim
丙型肝炎病毒mRNA含有一个内部核糖体进入位点（IRES），它介导末端非依赖性翻译起始，需要一个真核起始因子（eIF）的子集。生物化学研究表明，IRES与40 S核糖体亚基的直接结合将起始密码子置于P位点，在P位点处，其与eIF 2结合的Met-tRNAiMet碱基配对，形成48 S起始复合物。随后，eIF 5和eIF 5 B介导亚基连接，产生可延伸的80 S核糖体。起始也可以在没有eIF 2的情况下进行，在这种情况下，Met-tRNAiMet直接被eIF 5 B募集。然而，在HCV IRES上组装的起始复合物的结构、不同状态之间的转换以及伴随的构象变化仍然未知。为了填补这些空白，我们现在获得了IRES起始复合物的cryo-EM结构，分辨率高达3.5埃，涵盖了从最初的核糖体结合，通过含eIF 2的48 S起始复合物，到含eIF 5 B的复合物的所有主要阶段。这些结构提供了深入了解40 S/IRES接触的动态网络，突出IRES结构域II的作用，并揭示了从eIF 2到eIF 5 B的过渡过程中发生的构象变化，并为亚基连接做好准备。
Hepatitis C virus mRNA contains an internal ribosome entry site (IRES) that mediates end-independent translation initiation, requiring a subset of eukaryotic initiation factors (eIFs). Biochemical studies revealed that direct binding of the IRES to the 40S ribosomal subunit places the initiation codon into the P site, where it base pairs with eIF2-bound Met-tRNAiMet forming a 48S initiation complex. Subsequently, eIF5 and eIF5B mediate subunit joining, yielding an elongation-competent 80S ribosome. Initiation can also proceed without eIF2, in which case Met-tRNAiMet is recruited directly by eIF5B. However, the structures of initiation complexes assembled on the HCV IRES, the transitions between different states, and the accompanying conformational changes have remained unknown. To fill these gaps, we now obtained cryo-EM structures of IRES initiation complexes, at resolutions up to 3.5 angstrom, that cover all major stages from the initial ribosomal association, through eIF2-containing 48S initiation complexes, to eIF5B-containing complexes immediately prior to subunit joining. These structures provide insights into the dynamic network of 40S/IRES contacts, highlight the role of IRES domain II, and reveal conformational changes that occur during the transition from eIF2- to eIF5B-containing 48S complexes and prepare them for subunit joining.