Structure of monomeric yeast and mammalian Sec61 complexes interacting with the translating ribosome.
The trimeric Sec61/SecY complex is a protein-conducting channel (PCC) for secretory and membrane proteins. Although Sec complexes can form oligomers, it has been suggested that a single copy may serve as an active PCC. We determined subnanometer-resolution cryo-electron microscopy structures of eukaryotic ribosome-Sec61 complexes. In combination with biochemical data, we found that in both idle and active states, the Sec complex is not oligomeric and interacts mainly via two cytoplasmic loops with the universal ribosomal adaptor site. In the active state, the ribosomal tunnel and a central pore of the monomeric PCC were occupied by the nascent chain, contacting loop 6 of the Sec complex. This provides a structural basis for the activity of a solitary Sec complex in cotranslational protein translocation.
Becker
Thomas
T
Gene Center Munich and Center for Integrated Protein Science, Department of Chemistry and Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany.
Bhushan
Shashi
S
Jarasch
Alexander
A
Armache
Jean-Paul
JP
Funes
Soledad
S
Jossinet
Fabrice
F
Gumbart
James
J
Mielke
Thorsten
T
Berninghausen
Otto
O
Schulten
Klaus
K
Westhof
Eric
E
Gilmore
Reid
R
Mandon
Elisabet C
EC
Beckmann
Roland
R
D000818:Animals; D001665:Binding Sites; D020285:Cryoelectron Microscopy; D004285:Dogs; D007091:Image Processing, Computer-Assisted; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D008958:Models, Molecular; D014176:Protein Biosynthesis; D011487:Protein Conformation; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D021381:Protein Transport; D011506:Proteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D012270:Ribosomes / Q000378:metabolism* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure
D008565:Membrane Proteins; D011506:Proteins; C499381:SSH1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins