Structures of the E. coli translating ribosome with SRP and its receptor and with the translocon

Nat Commun. 2016 Jan 25:7:10471. doi: 10.1038/ncomms10471.


Co-translational protein targeting to membranes is a universally conserved process. Central steps include cargo recognition by the signal recognition particle and handover to the Sec translocon. Here we present snapshots of key co-translational-targeting complexes solved by cryo-electron microscopy at near-atomic resolution, establishing the molecular contacts between the Escherichia coli translating ribosome, the signal recognition particle and the translocon. Our results reveal the conformational changes that regulate the latching of the signal sequence, the release of the heterodimeric domains of the signal recognition particle and its receptor, and the handover of the signal sequence to the translocon. We also observe that the signal recognition particle and the translocon insert-specific structural elements into the ribosomal tunnel to remodel it, possibly to sense nascent chains. Our work provides structural evidence for a conformational state of the signal recognition particle and its receptor primed for translocon binding to the ribosome-nascent chain complex.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Codon / genetics*
  • Codon / metabolism
  • Cryoelectron Microscopy
  • Escherichia coli / chemistry
  • Escherichia coli / genetics*
  • Escherichia coli / metabolism
  • Escherichia coli Proteins / genetics*
  • Escherichia coli Proteins / metabolism
  • Models, Molecular
  • Protein Binding
  • Protein Biosynthesis
  • Protein Transport
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Receptors, Cytoplasmic and Nuclear / chemistry*
  • Receptors, Cytoplasmic and Nuclear / genetics
  • Receptors, Cytoplasmic and Nuclear / metabolism
  • Receptors, Peptide / chemistry*
  • Receptors, Peptide / genetics
  • Receptors, Peptide / metabolism
  • Ribosomes / chemistry*
  • Ribosomes / genetics
  • Ribosomes / metabolism
  • Signal Recognition Particle / chemistry*
  • Signal Recognition Particle / genetics
  • Signal Recognition Particle / metabolism
  • Transcription Factors / genetics
  • Transcription Factors / metabolism


  • Codon
  • Escherichia coli Proteins
  • RNA, Messenger
  • Receptors, Cytoplasmic and Nuclear
  • Receptors, Peptide
  • SecM protein, E coli
  • Signal Recognition Particle
  • Transcription Factors
  • signal peptide receptor