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Compact IF2 allows initiator tRNA accommodation into the P site and gates the ribosome to elongation. 2022

Ritwika S Basu, and Michael B Sherman, and Matthieu G Gagnon
Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, TX, 77555, USA.

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.

UI MeSH Term Description Entries
D006160 Guanosine Triphosphate Guanosine 5'-(tetrahydrogen triphosphate). A guanine nucleotide containing three phosphate groups esterified to the sugar moiety. GTP,Triphosphate, Guanosine
D012270 Ribosomes Multicomponent ribonucleoprotein structures found in the CYTOPLASM of all cells, and in MITOCHONDRIA, and PLASTIDS. They function in PROTEIN BIOSYNTHESIS via GENETIC TRANSLATION. Ribosome
D012358 RNA, Transfer, Met A transfer RNA which is specific for carrying methionine to sites on the ribosomes. During initiation of protein synthesis, tRNA(f)Met in prokaryotic cells and tRNA(i)Met in eukaryotic cells binds to the start codon (CODON, INITIATOR). Initiator tRNA,Methionine-Specific tRNA,Methionine-Specific tRNAm,RNA, Transfer, Initiator,Transfer RNA, Met,tRNA(f)Met,tRNA(i)Met,tRNA(m)Met,tRNAMet,tRNA(Met),Met Transfer RNA,Methionine Specific tRNA,Methionine Specific tRNAm,RNA, Met Transfer,tRNA, Initiator,tRNA, Methionine-Specific,tRNAm, Methionine-Specific
D020285 Cryoelectron Microscopy Electron microscopy involving rapid freezing of the samples. The imaging of frozen-hydrated molecules and organelles permits the best possible resolution closest to the living state, free of chemical fixatives or stains. Electron Cryomicroscopy,Cryo-electron Microscopy,Cryo electron Microscopy,Cryo-electron Microscopies,Cryoelectron Microscopies,Cryomicroscopies, Electron,Cryomicroscopy, Electron,Electron Cryomicroscopies,Microscopies, Cryo-electron,Microscopies, Cryoelectron,Microscopy, Cryo-electron,Microscopy, Cryoelectron
D039881 Prokaryotic Initiation Factor-2 The largest of the three prokaryotic initiation factors with a molecular size of approximately 80 kD. It functions in the transcription initiation process by promoting the binding of formylmethionine-tRNA to the P-site of the 30S ribosome and by preventing the incorrect binding of elongator tRNA to the translation initiation site. Peptide Initiation Factor IF-2,IF2 Protein,Initiation Factor-2,Peptide Initiation Factor 2,Translational Initiation Factor 2,infB Gene Product,infB Protein,Initiation Factor 2,Initiation Factor-2, Prokaryotic,Peptide Initiation Factor IF 2,Prokaryotic Initiation Factor 2

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