Compact IF2 allows initiator tRNA accommodation into the P site and gates the ribosome to elongation

Ritwika S. Basu, Michael B. Sherman and Matthieu G. Gagnon ()
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Ritwika S. Basu: University of Texas Medical Branch
Michael B. Sherman: University of Texas Medical Branch
Matthieu G. Gagnon: University of Texas Medical Branch

Nature Communications, 2022, vol. 13, issue 1, 1-12

Abstract: Abstract During translation initiation, initiation factor 2 (IF2) holds initiator transfer RNA (fMet-tRNAifMet) in a specific orientation in the peptidyl (P) site of the ribosome. Upon subunit joining IF2 hydrolyzes GTP and, concomitant with inorganic phosphate (Pi) release, changes conformation facilitating fMet-tRNAifMet accommodation into the P site and transition of the 70 S ribosome initiation complex (70S-IC) to an elongation-competent ribosome. The mechanism by which IF2 separates from initiator tRNA at the end of translation initiation remains elusive. Here, we report cryo-electron microscopy (cryo-EM) structures of the 70S-IC from Pseudomonas aeruginosa bound to compact IF2-GDP and initiator tRNA. Relative to GTP-bound IF2, rotation of the switch 2 α-helix in the G-domain bound to GDP unlocks a cascade of large-domain movements in IF2 that propagate to the distal tRNA-binding domain C2. The C2-domain relocates 35 angstroms away from tRNA, explaining how IF2 makes way for fMet-tRNAifMet accommodation into the P site. Our findings provide the basis by which IF2 gates the ribosome to the elongation phase.

Date: 2022
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DOI: 10.1038/s41467-022-31129-2

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