EMD-13180
Cryo-EM structure of 70S ribosome stalled with TnaC peptide (control)
EMD-13180
Single-particle2.9 Å
Deposition: 08/07/2021
Map released: 27/10/2021
Last modified: 13/11/2024
Sample Organism:
Escherichia coli K-12
Sample: 70S ribosome
Fitted models: 7p3k (Avg. Q-score: 0.541)
Deposition Authors: Buschauer R, Komar T
Sample: 70S ribosome
Fitted models: 7p3k (Avg. Q-score: 0.541)
Deposition Authors: Buschauer R, Komar T
Structural basis of l-tryptophan-dependent inhibition of release factor 2 by the TnaC arrest peptide.
Su T,
Kudva R,
Becker T,
Buschauer R,
Komar T ,
Berninghausen O,
von Heijne G,
Cheng J ,
Beckmann R
(2021) Nucleic Acids Res , 49 , 9539 - 9547
(2021) Nucleic Acids Res , 49 , 9539 - 9547
Abstract:
In Escherichia coli, elevated levels of free l-tryptophan (l-Trp) promote translational arrest of the TnaC peptide by inhibiting its termination. However, the mechanism by which translation-termination by the UGA-specific decoding release factor 2 (RF2) is inhibited at the UGA stop codon of stalled TnaC-ribosome-nascent chain complexes has so far been ambiguous. This study presents cryo-EM structures for ribosomes stalled by TnaC in the absence and presence of RF2 at average resolutions of 2.9 and 3.5 Å, respectively. Stalled TnaC assumes a distinct conformation composed of two small α-helices that act together with residues in the peptide exit tunnel (PET) to coordinate a single L-Trp molecule. In addition, while the peptidyl-transferase center (PTC) is locked in a conformation that allows RF2 to adopt its canonical position in the ribosome, it prevents the conserved and catalytically essential GGQ motif of RF2 from adopting its active conformation in the PTC. This explains how translation of the TnaC peptide effectively allows the ribosome to function as a L-Trp-specific small-molecule sensor that regulates the tnaCAB operon.
In Escherichia coli, elevated levels of free l-tryptophan (l-Trp) promote translational arrest of the TnaC peptide by inhibiting its termination. However, the mechanism by which translation-termination by the UGA-specific decoding release factor 2 (RF2) is inhibited at the UGA stop codon of stalled TnaC-ribosome-nascent chain complexes has so far been ambiguous. This study presents cryo-EM structures for ribosomes stalled by TnaC in the absence and presence of RF2 at average resolutions of 2.9 and 3.5 Å, respectively. Stalled TnaC assumes a distinct conformation composed of two small α-helices that act together with residues in the peptide exit tunnel (PET) to coordinate a single L-Trp molecule. In addition, while the peptidyl-transferase center (PTC) is locked in a conformation that allows RF2 to adopt its canonical position in the ribosome, it prevents the conserved and catalytically essential GGQ motif of RF2 from adopting its active conformation in the PTC. This explains how translation of the TnaC peptide effectively allows the ribosome to function as a L-Trp-specific small-molecule sensor that regulates the tnaCAB operon.