title: Visualization of a polytopic membrane protein during SecY-mediated membrane insertion.
abstract: The biogenesis of polytopic membrane proteins occurs co-translationally on ribosomes that are tightly bound to a membrane-embedded protein-conducting channel: the Sec-complex. The path that is followed by nascent proteins inside the ribosome and the Sec-complex is relatively well established; however, it is not clear what the fate of the N-terminal transmembrane domains (TMDs) of polytopic membrane proteins is when the C-terminal TMDs domains are not yet synthesized. Here, we present the sub-nanometer cryo-electron microscopy structure of an in vivo generated ribosome-SecY complex that carries a membrane insertion intermediate of proteorhodopsin (PR). The structure reveals a pre-opened Sec-complex and the first two TMDs of PR already outside the SecY complex directly in front of its proposed lateral gate. Thus, our structure is in agreement with positioning of N-terminal TMDs at the periphery of SecY, and in addition, it provides clues for the molecular mechanism underlying membrane protein topogenesis.
authors.affiliation: Department of Biochemistry, Gene Center and Center for integrated Protein Science Munich, Feodor-Lynen-Strasse 25, University of Munich, 81377 Munich, Germany.
authors.forename: Lukas
authors.initials: L
authors.lastname: Bischoff
authors.affiliation: Department of Biochemistry, Gene Center and Center for integrated Protein Science Munich, Feodor-Lynen-Strasse 25, University of Munich, 81377 Munich, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Wickles
authors.affiliation: Department of Biochemistry, Gene Center and Center for integrated Protein Science Munich, Feodor-Lynen-Strasse 25, University of Munich, 81377 Munich, Germany.
authors.forename: Otto
authors.initials: O
authors.lastname: Berninghausen
authors.affiliation: Department of Biochemistry, Gene Center and Center for integrated Protein Science Munich, Feodor-Lynen-Strasse 25, University of Munich, 81377 Munich, Germany.
authors.forename: Eli O
authors.initials: EO
authors.lastname: van der Sluis
authors.affiliation: Department of Biochemistry, Gene Center and Center for integrated Protein Science Munich, Feodor-Lynen-Strasse 25, University of Munich, 81377 Munich, Germany.
authors.forename: Roland
authors.initials: R
authors.lastname: Beckmann
mesh_terms: D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure*; D020285:Cryoelectron Microscopy; D004926:Escherichia coli; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000378:metabolism / Q000648:ultrastructure*; D008958:Models, Molecular; D011487:Protein Conformation; D000069816:SEC Translocation Channels
chemical_list: D029968:Escherichia coli Proteins; D000069816:SEC Translocation Channels; C057841:SecY protein, E coli