Structural insight into the protein translocation channel
A structurally conserved protein translocation channel is formed by the heterotrimeric Sec61 complex in eukaryotes, and SecY complex in archaea and bacteria. Electron microscopy studies suggest that the channel may function as an oligomeric assembly of Sec61 or SecY complexes. Remarkably, the recently determined X-ray structure of an archaeal SecY complex indicates that the pore is located at the center of a single molecule of the complex. This structure suggests how the pore opens perpendicular to the plane of the membrane to allow the passage of newly synthesized secretory proteins across the membrane and opens laterally to allow transmembrane segments of nascent membrane proteins to enter the lipid bilayer. The electron microscopy and X-ray results together suggest that only one copy of the SecY or Sec61 complex within an oligomer translocates a polypeptide chain at any given time.
© 2004 Elsevier. Available online 21 July 2004. We thank AR Osborne and B van den Berg for critical reading of the manuscript. WMC was supported by a Damon-Runyon Cancer Research Foundation fellowship. Both TAR and CWA are supported by National Institutes of Health grants. TAR is an investigator of the Howard Hughes Medical Institute.