Molecular basis for the ribosome functioning as an L-tryptophan sensor.
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Bischoff L, Berninghausen O, Beckmann R
Molecular basis for the ribosome functioning as an L-tryptophan sensor.
Cell Rep. 2014 Oct 23;9(2):469-75. doi: 10.1016/j.celrep.2014.09.011. Epub 2014 Oct 9.
- PubMed ID
- 25310980 [ View in PubMed]
- Abstract
Elevated levels of the free amino acid L-tryptophan (L-Trp) trigger expression of the tryptophanase tnaCAB operon in E. coli. Activation depends on tryptophan-dependent ribosomal stalling during translation of the upstream TnaC peptide. Here, we present a cryoelectron microscopy (cryo-EM) reconstruction at 3.8 A resolution of a ribosome stalled by the TnaC peptide. Unexpectedly, we observe two L-Trp molecules in the ribosomal exit tunnel coordinated within composite hydrophobic pockets formed by the nascent TnaC peptide and the tunnel wall. As a result, the peptidyl transferase center (PTC) adopts a distinct conformation that precludes productive accommodation of release factor 2 (RF2), thereby inducing translational stalling. Collectively, our results demonstrate how the translating ribosome can act as a small molecule sensor for gene regulation.