Thomas Becker, Elisabet Mandon, Shashi Bhushan, Alexander Jarasch, Jean-Paul
Armache, Soledad Funes, Fabrice Jossinet, James Gumbart, Thorsten Mielke,
Otto Berninghausen, Klaus Schulten, Eric Westhof, Reid Gilmore, and Roland
Beckmann.
Structure of monomeric yeast and mammalian Sec61 complexes
interacting with the translating ribosome.
Science, 2009.
Published online October 29 2009; 10.1126/science.1178535.
BECK2009
The trimeric Sec61/SecY complex is serving a vital function as a protein-conducting
channel (PCC) for secretory and membrane proteins. Although Sec complexes can form
oligomers, the crystal structures of prokaryotic SecY complexes and other data suggest
that a single copy may serve as an active PCC. Here, we present sub-nanometer resolution
cryo-EM structures of eukaryotic ribosome-Sec61 complexes in combination with
biochemical data demonstrating that in both states, idle and active, the Sec complex is
non-oligomeric and interacts mainly via loop 8 with the universal ribosomal adaptor site.
In the active state the ribosomal tunnel and a central pore of the monomeric PCC are
occupied by the nascent chain contacting loop 6 of the Sec complex. Our findings provide
the structural basis for understanding the activity of a solitary Sec complex in
cotranslational translocation.
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