Structure of the quaternary complex between SRP, SR, and translocon bound to the translating ribosome

Nat Commun. 2017 May 19:8:15470. doi: 10.1038/ncomms15470.

Abstract

During co-translational protein targeting, the signal recognition particle (SRP) binds to the translating ribosome displaying the signal sequence to deliver it to the SRP receptor (SR) on the membrane, where the signal peptide is transferred to the translocon. Using electron cryo-microscopy, we have determined the structure of a quaternary complex of the translating Escherichia coli ribosome, the SRP-SR in the 'activated' state and the translocon. Our structure, supported by biochemical experiments, reveals that the SRP RNA adopts a kinked and untwisted conformation to allow repositioning of the 'activated' SRP-SR complex on the ribosome. In addition, we observe the translocon positioned through interactions with the SR in the vicinity of the ribosome exit tunnel where the signal sequence is extending beyond its hydrophobic binding groove of the SRP M domain towards the translocon. Our study provides new insights into the mechanism of signal sequence transfer from the SRP to the translocon.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cryoelectron Microscopy
  • Escherichia coli / metabolism*
  • Escherichia coli Proteins / metabolism*
  • GTP Phosphohydrolases / metabolism
  • Hydrophobic and Hydrophilic Interactions
  • Molecular Docking Simulation
  • Mutation
  • Protein Binding
  • Protein Biosynthesis
  • Protein Sorting Signals / genetics
  • Protein Structure, Quaternary
  • Protein Transport
  • Receptors, Cytoplasmic and Nuclear / metabolism*
  • Receptors, Peptide / metabolism*
  • Ribosomes / metabolism*
  • Signal Recognition Particle / metabolism*

Substances

  • Escherichia coli Proteins
  • Protein Sorting Signals
  • Receptors, Cytoplasmic and Nuclear
  • Receptors, Peptide
  • Signal Recognition Particle
  • signal peptide receptor
  • GTP Phosphohydrolases