TCB Publications - Paper Request

Thomas Becker, Shashi Bhushan, Alexander Jarasch, Jean-Paul Armache, Soledad Funes, Fabrice Jossinet, James Gumbart, Thorsten Mielke, Otto Berninghausen, Klaus Schulten, Eric Westhof, Reid Gilmore, Elisabet C. Mandon, and Roland Beckmann. Structure of monomeric yeast and mammalian Sec61 complexes interacting with the translating ribosome. Science, 326:1369-1373, 2009.

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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