9cg5
70S initiation complex (tRNA-fMet M1 + UUG start codon)
Structural highlights
FunctionPublication Abstract from PubMedTranslation initiation is a highly regulated, multi-step process which is critical for efficient and accurate protein synthesis. In bacteria, initiation begins when mRNA, initiation factors, and a dedicated initiator fMet-tRNA(fMet) bind the small (30S) ribosomal subunit. Specific binding of fMet-tRNA(fMet) in the peptidyl (P) site is mediated by the inspection of the fMet moiety by initiation factor IF2 and of three conserved G-C base pairs in the tRNA anticodon stem by the 30S head domain. Tandem A-minor interactions form between 16S ribosomal RNA nucleotides A1339 and G1338 and tRNA base pairs G30-C40 and G29-C41, respectively. Swapping the G30-C40 pair of tRNA(fMet) with C-G reduces discrimination against the noncanonical start codon CUG in vitro, suggesting crosstalk between gripping of the anticodon stem and recognition of the start codon. Here, we solved electron cryomicroscopy structures of E. coli 70S initiation complexes containing an fMet-tRNA(fMet) G30-C40 variant paired to noncanonical CUG start codon, in the presence or absence of IF2 and the non-hydrolyzable GTP analog GDPCP, alongside structures of 70S initiation complexes containing this tRNA(fMet) variant paired to the canonical bacterial start codons AUG, GUG, and UUG. We find that the M1 mutation weakens A-minor interactions between tRNA(fMet) and 16S nucleotides A1339 and G1338, with IF2 strengthening the interaction of G1338 with the tRNA minor groove. These structures suggest how even slight changes to the recognition of the fMet-tRNA(fMet) anticodon stem by the ribosome can impact start codon selection. Structural analysis of noncanonical translation initiation complexes.,Mattingly JM, Nguyen HA, Roy B, Fredrick K, Dunham CM J Biol Chem. 2024 Aug 31:107743. doi: 10.1016/j.jbc.2024.107743. PMID:39222680[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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