![]() The current structural knowledge about dynamics of the eukaryotic elongation cycle has been provided by low-to-intermediate resolution cryo-electron microscopy (cryo-EM) reconstructions 6, 7, 8, 9, 10. Diphthamide is a target of several virulent toxins that inactivate eEF2 by ADP ribosylation and cause lethal effects 5. Organisms lacking diphthamide have reduced protein synthesis rates and increased occurrence of (−1) frameshifting 1, 4. Many genetic and biochemical studies point to a critical role of the unique eEF2 post-translational modification diphthamide, which is located in domain IV and is conserved among eukaryotes and archaea. In eukaryotes, the complex process of translocation is ensured by eEF2, a GTPase that is indispensable for maintaining the correct mRNA reading frame. This model suggests how eukaryote-specific elements of the 80S ribosome, eEF2 and tRNAs undergo large-scale molecular reorganizations to ensure maintenance of the mRNA reading frame during the complex process of translocation. The model demonstrates how the decoding centre releases a codon–anticodon duplex, allowing its movement on the ribosome, and emphasizes the function of eEF2 as a ‘pawl’ defining the directionality of translocation 3. ![]() The crystal structure reveals a network of stabilization of codon–anticodon interactions involving diphthamide 1 and the hypermodified nucleoside wybutosine at position 37 of phenylalanine tRNA, which is also known to enhance translation accuracy 2. Here we report a high-resolution X-ray structure of the eukaryotic 80S ribosome in a translocation-intermediate state containing mRNA, naturally modified eEF2 and tRNAs. Although numerous studies point to critical roles for both the conserved eukaryotic posttranslational modification diphthamide in eEF2 and tRNA modifications in supporting the accuracy of translocation, detailed molecular mechanisms describing their specific functions are poorly understood. In eukaryotes translocation is ensured by elongation factor 2 (eEF2), which catalyses the process and actively contributes to its accuracy 1. Translation of the genetic code into proteins is realized through repetitions of synchronous translocation of messenger RNA (mRNA) and transfer RNAs (tRNA) through the ribosome.
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