title: Structure of monomeric yeast and mammalian Sec61 complexes interacting with the translating ribosome.
abstract: 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.
authors.affiliation: 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.
authors.forename: Thomas
authors.initials: T
authors.lastname: Becker
authors.forename: Shashi
authors.initials: S
authors.lastname: Bhushan
authors.forename: Alexander
authors.initials: A
authors.lastname: Jarasch
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Armache
authors.forename: Soledad
authors.initials: S
authors.lastname: Funes
authors.forename: Fabrice
authors.initials: F
authors.lastname: Jossinet
authors.forename: James
authors.initials: J
authors.lastname: Gumbart
authors.forename: Thorsten
authors.initials: T
authors.lastname: Mielke
authors.forename: Otto
authors.initials: O
authors.lastname: Berninghausen
authors.forename: Klaus
authors.initials: K
authors.lastname: Schulten
authors.forename: Eric
authors.initials: E
authors.lastname: Westhof
authors.forename: Reid
authors.initials: R
authors.lastname: Gilmore
authors.forename: Elisabet C
authors.initials: EC
authors.lastname: Mandon
authors.forename: Roland
authors.initials: R
authors.lastname: Beckmann
mesh_terms: 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
chemical_list: D008565:Membrane Proteins; D011506:Proteins; C499381:SSH1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins