7ac7
Structure of accomodated trans-translation complex on E. Coli stalled ribosome.
Structural highlights
FunctionSSRP_ECOLI Required for rescue of stalled ribosomes mediated by trans-translation. Binds to tmRNA RNA (also known as SsrA or 10Sa RNA, 363 nucleotides in this organism), required for stable binding of tmRNA to ribosomes (PubMed:10393194, PubMed:11904185, PubMed:11917023). tmRNA and SmpB together mimic tRNA shape, replacing the anticodon stem-loop with SmpB (Probable). tmRNA is encoded by the ssrA gene; the 2 termini fold to resemble tRNA(Ala) and it encodes a 'tag peptide', a short internal open reading frame. Able to recruit charged tmRNA to ribosomes (PubMed:15069072). Does not play a role in transcription, processing or Ala-aminoacylation of tmRNA (PubMed:10393194). Other studies have shown it stimulates aminoacylation of tmRNA (PubMed:11917023, PubMed:11904185). May protect tmRNA from degradation (PubMed:11917023). Binds to tmRNA that cannot be aminoacylated (tmRNA G3A), does not bind to tmRNA mutations near the tRNA-like termini (tmRNA G19C, A334U); other tmRNA mutations that block trans-translation still bind SmpB (PubMed:11917023). With tmRNA may play a role in bacterial persistence (PubMed:23812681). During trans-translation Ala-aminoacylated transfer-messenger RNA acts like a tRNA, entering the A-site of stalled ribosomes, displacing the stalled mRNA. The ribosome then switches to translate the ORF on the tmRNA, the nascent peptide is terminated with the 'tag peptide' encoded by the tmRNA and targeted for degradation. The ribosome is freed to recommence translation, which seems to be the essential function of trans-translation.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] Publication Abstract from PubMedIn bacteria, trans-translation is the main rescue system, freeing ribosomes stalled on defective messenger RNAs. This mechanism is driven by small protein B (SmpB) and transfer-messenger RNA (tmRNA), a hybrid RNA known to have both a tRNA-like and an mRNA-like domain. Here we present four cryo-EM structures of the ribosome during trans-translation at resolutions from 3.0 to 3.4 A. These include the high-resolution structure of the whole pre-accommodated state, as well as structures of the accommodated state, the translocated state, and a translocation intermediate. Together, they shed light on the movements of the tmRNA-SmpB complex in the ribosome, from its delivery by the elongation factor EF-Tu to its passage through the ribosomal A and P sites after the opening of the B1 bridges. Additionally, we describe the interactions between the tmRNA-SmpB complex and the ribosome. These explain why the process does not interfere with canonical translation. Structures of tmRNA and SmpB as they transit through the ribosome.,Guyomar C, D'Urso G, Chat S, Giudice E, Gillet R Nat Commun. 2021 Aug 13;12(1):4909. doi: 10.1038/s41467-021-24881-4. PMID:34389707[11] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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