Structure of the E. coli protein-conducting channel bound to a translating ribosome

Nature. 2005 Nov 17;438(7066):318-24. doi: 10.1038/nature04133.


Secreted and membrane proteins are translocated across or into cell membranes through a protein-conducting channel (PCC). Here we present a cryo-electron microscopy reconstruction of the Escherichia coli PCC, SecYEG, complexed with the ribosome and a nascent chain containing a signal anchor. This reconstruction shows a messenger RNA, three transfer RNAs, the nascent chain, and detailed features of both a translocating PCC and a second, non-translocating PCC bound to mRNA hairpins. The translocating PCC forms connections with ribosomal RNA hairpins on two sides and ribosomal proteins at the back, leaving a frontal opening. Normal mode-based flexible fitting of the archaeal SecYEbeta structure into the PCC electron microscopy densities favours a front-to-front arrangement of two SecYEG complexes in the PCC, and supports channel formation by the opening of two linked SecY halves during polypeptide translocation. On the basis of our observation in the translocating PCC of two segregated pores with different degrees of access to bulk lipid, we propose a model for co-translational protein translocation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Cell Membrane / chemistry
  • Cell Membrane / metabolism
  • Cryoelectron Microscopy
  • Escherichia coli Proteins / biosynthesis
  • Escherichia coli Proteins / chemistry*
  • Escherichia coli Proteins / metabolism*
  • Membrane Proteins / chemistry
  • Membrane Proteins / metabolism
  • Models, Molecular
  • Multiprotein Complexes / chemistry
  • Multiprotein Complexes / metabolism
  • Pliability
  • Protein Binding
  • Protein Biosynthesis*
  • Protein Structure, Quaternary
  • Protein Transport
  • Ribosomes / metabolism*
  • SEC Translocation Channels


  • Escherichia coli Proteins
  • Membrane Proteins
  • Multiprotein Complexes
  • SEC Translocation Channels
  • SecE protein, E coli
  • SecG protein, E coli
  • SecY protein, E coli

Associated data

  • PDB/2AKH
  • PDB/2AKI