Structure of the Mammalian Ribosomal 43S Preinitiation Complex Bound to the Scanning Factor DHX29

• Published in: Cell Vol. 153; no. 5; pp. 1108 - 1119
• Main Authors: Hashem, Yaser, des Georges, Amedee, Dhote, Vidya, Langlois, Robert, Liao, Hstau Y., Grassucci, Robert A., Hellen, Christopher U.T., Pestova, Tatyana V., Frank, Joachim
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 23-05-2013
• Subjects: Animals; Base Sequence; Cell-Free System; Cryoelectron Microscopy; Eukaryotic Initiation Factor-2 - chemistry; Eukaryotic Initiation Factor-2 - metabolism; Humans; Mammals - genetics; Mammals - metabolism; Models, Molecular; Molecular Sequence Data; Peptide Chain Initiation, Translational; Rabbits; Ribonucleoproteins - chemistry; Ribonucleoproteins - metabolism; RNA Helicases - chemistry; RNA Helicases - metabolism; RNA, Ribosomal - chemistry; RNA, Ribosomal - metabolism; RNA, Ribosomal, 18S - chemistry; RNA, Ribosomal, 18S - metabolism
• ISSN: 0092-8674; 1097-4172
• DOI: 10.1016/j.cell.2013.04.036

Eukaryotic translation initiation begins with assembly of a 43S preinitiation complex. First, methionylated initiator methionine transfer RNA (Met-tRNAiMet), eukaryotic initiation factor (eIF) 2, and guanosine triphosphate form a ternary complex (TC). The TC, eIF3, eIF1, and eIF1A cooperatively bind to the 40S subunit, yielding the 43S preinitiation complex, which is ready to attach to messenger RNA (mRNA) and start scanning to the initiation codon. Scanning on structured mRNAs additionally requires DHX29, a DExH-box protein that also binds directly to the 40S subunit. Here, we present a cryo-electron microscopy structure of the mammalian DHX29-bound 43S complex at 11.6 Å resolution. It reveals that eIF2 interacts with the 40S subunit via its α subunit and supports Met-tRNAiMet in an unexpected P/I orientation (eP/I). The structural core of eIF3 resides on the back of the 40S subunit, establishing two principal points of contact, whereas DHX29 binds around helix 16. The structure provides insights into eukaryote-specific aspects of translation, including the mechanism of action of DHX29.
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•The eIF3e core binds the 40S subunit via ribosomal proteins S1e, S13e, S26e, and S27e•eIF2 binds the 40S subunit via interaction of the eIF2a-D1 domain with ribosomal protein S5e•Initiator transfer RNA adopts an unexpected P/I orientation close to that in prokaryotic initiation•In DHX29-43S complexes, DHX29 binds h16 of 18S ribosomal RNA, and the mRNA latch is closed
The DHX29 helicase promotes mRNA scanning of the 40S ribosome for translation initiation, and a new structure provides insights into eukaryote-specific aspects of initiation, including how initiator transfer RNA, eIF2, eIF3, and DHX29 interact with the 40S subunit.