Ribosome binding of a single copy of the SecY complex: implications for protein translocation

Mol Cell. 2007 Dec 28;28(6):1083-92. doi: 10.1016/j.molcel.2007.10.034.


The SecY complex associates with the ribosome to form a protein translocation channel in the bacterial plasma membrane. We have used cryo-electron microscopy and quantitative mass spectrometry to show that a nontranslating E. coli ribosome binds to a single SecY complex. The crystal structure of an archaeal SecY complex was then docked into the electron density maps. In the resulting model, two cytoplasmic loops of SecY extend into the exit tunnel near proteins L23, L29, and L24. The loop between transmembrane helices 8 and 9 interacts with helices H59 and H50 in the large subunit RNA, while the 6/7 loop interacts with H7. We also show that point mutations of basic residues within either loop abolish ribosome binding. We suggest that SecY binds to this primary site on the ribosome and subsequently captures and translocates the nascent chain.

Publication types

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

MeSH terms

  • Archaeal Proteins / chemistry
  • Archaeal Proteins / genetics
  • Archaeal Proteins / metabolism
  • Cell Membrane / metabolism*
  • Cryoelectron Microscopy
  • Crystallization
  • Electrophoresis, Polyacrylamide Gel
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism*
  • Models, Molecular
  • Point Mutation
  • Protein Binding
  • Protein Structure, Tertiary
  • Protein Transport
  • RNA, Ribosomal / metabolism
  • Ribosomes / chemistry
  • Ribosomes / metabolism*
  • Ribosomes / ultrastructure
  • SEC Translocation Channels


  • Archaeal Proteins
  • Escherichia coli Proteins
  • RNA, Ribosomal
  • SEC Translocation Channels
  • SecY protein, E coli

Associated data

  • PDB/3BO0
  • PDB/3BO1