title: Three-dimensional structure of the bacterial protein-translocation complex SecYEG.
abstract: Transport and membrane integration of polypeptides is carried out by specific protein complexes in the membranes of all living cells. The Sec transport path provides an essential and ubiquitous route for protein translocation. In the bacterial cytoplasmic membrane, the channel is formed by oligomers of a heterotrimeric membrane protein complex consisting of subunits SecY, SecE and SecG. In the endoplasmic reticulum membrane, the channel is formed from the related Sec61 complex. Here we report the structure of the Escherichia coli SecYEG assembly at an in-plane resolution of 8 A. The three-dimensional map, calculated from two-dimensional SecYEG crystals, reveals a sandwich of two membranes interacting through the extensive cytoplasmic domains. Each membrane is composed of dimers of SecYEG. The monomeric complex contains 15 transmembrane helices. In the centre of the dimer we observe a 16 x 25 A cavity closed on the periplasmic side by two highly tilted transmembrane helices. This may represent the closed state of the protein-conducting channel.
authors.affiliation: Max-Planck-Institut für Biophysik, Abteilung Strukturbiologie, Heinrich-Hoffmann-Strasse 7, 60528 Frankfurt am Main, Germany. Cecile.Breyton@ibpc.fr
authors.forename: Cécile
authors.initials: C
authors.lastname: Breyton
authors.forename: Winfried
authors.initials: W
authors.lastname: Haase
authors.forename: Tom A
authors.initials: TA
authors.lastname: Rapoport
authors.forename: Werner
authors.initials: W
authors.lastname: Kühlbrandt
authors.forename: Ian
authors.initials: I
authors.lastname: Collinson
mesh_terms: D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D020285:Cryoelectron Microscopy; D003460:Crystallization; D019281:Dimerization; D004926:Escherichia coli / Q000737:chemistry* / Q000166:cytology; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D021381:Protein Transport; D000069816:SEC Translocation Channels
chemical_list: D029968:Escherichia coli Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D021122:Protein Subunits; D000069816:SEC Translocation Channels; C065493:SecE protein, E coli; C088616:SecG protein, E coli; C057841:SecY protein, E coli