title: A central cavity within the holo-translocon suggests a mechanism for membrane protein insertion.
abstract: The conserved SecYEG protein-conducting channel and the accessory proteins SecDF-YajC and YidC constitute the bacterial holo-translocon (HTL), capable of protein-secretion and membrane-protein insertion. By employing an integrative approach combining small-angle neutron scattering (SANS), low-resolution electron microscopy and biophysical analyses we determined the arrangement of the proteins and lipids within the super-complex. The results guided the placement of X-ray structures of individual HTL components and allowed the proposal of a model of the functional translocon. Their arrangement around a central lipid-containing pool conveys an unexpected, but compelling mechanism for membrane-protein insertion. The periplasmic domains of YidC and SecD are poised at the protein-channel exit-site of SecY, presumably to aid the emergence of translocating polypeptides. The SecY lateral gate for membrane-insertion is adjacent to the membrane 'insertase' YidC. Absolute-scale SANS employing a novel contrast-match-point analysis revealed a dynamic complex adopting open and compact configurations around an adaptable central lipid-filled chamber, wherein polytopic membrane-proteins could fold, sheltered from aggregation and proteolysis.
authors.affiliation: European Molecular Biology Laboratory, Grenoble Outstation, 71 Avenue des Martyrs, 38042 Grenoble, France.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Botte
authors.affiliation: School of Biochemistry, University of Bristol, BS8 1TD, United Kingdom.
authors.forename: Nathan R
authors.initials: NR
authors.lastname: Zaccai
authors.affiliation: European Molecular Biology Laboratory, Grenoble Outstation, 71 Avenue des Martyrs, 38042 Grenoble, France.
authors.forename: Jelger Lycklama À
authors.initials: JL
authors.lastname: Nijeholt
authors.affiliation: School of Biochemistry, University of Bristol, BS8 1TD, United Kingdom.
authors.forename: Remy
authors.initials: R
authors.lastname: Martin
authors.affiliation: European Molecular Biology Laboratory, Grenoble Outstation, 71 Avenue des Martyrs, 38042 Grenoble, France.
authors.forename: Kèvin
authors.initials: K
authors.lastname: Knoops
authors.affiliation: Department of Integrated Structural Biology, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), U964 INSERM, UMR7104 CNRS; University of Strasbourg, 1 Rue Laurent Fries, BP10142, 67404 Illkirch, France.
authors.forename: Gabor
authors.initials: G
authors.lastname: Papai
authors.affiliation: Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, EH9 3JR, United Kingdom.
authors.forename: Juan
authors.initials: J
authors.lastname: Zou
authors.affiliation: European Molecular Biology Laboratory, Grenoble Outstation, 71 Avenue des Martyrs, 38042 Grenoble, France.
authors.forename: Aurélien
authors.initials: A
authors.lastname: Deniaud
authors.affiliation: European Molecular Biology Laboratory, Grenoble Outstation, 71 Avenue des Martyrs, 38042 Grenoble, France.
authors.forename: Manikandan
authors.initials: M
authors.lastname: Karuppasamy
authors.affiliation: European Molecular Biology Laboratory, Grenoble Outstation, 71 Avenue des Martyrs, 38042 Grenoble, France.
authors.forename: Qiyang
authors.initials: Q
authors.lastname: Jiang
authors.affiliation: Department of Physics, University of Illinois Urbana Champaign, 3217 Beckman Institute, 405 N Mathews Ave., Urbana, IL 61801, USA.
authors.forename: Abhishek Singha
authors.initials: AS
authors.lastname: Roy
authors.affiliation: Department of Physics, University of Illinois Urbana Champaign, 3217 Beckman Institute, 405 N Mathews Ave., Urbana, IL 61801, USA.
authors.forename: Klaus
authors.initials: K
authors.lastname: Schulten
authors.affiliation: Department of Integrated Structural Biology, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), U964 INSERM, UMR7104 CNRS; University of Strasbourg, 1 Rue Laurent Fries, BP10142, 67404 Illkirch, France.
authors.forename: Patrick
authors.initials: P
authors.lastname: Schultz
authors.affiliation: Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, EH9 3JR, United Kingdom.|Department of Bioanalytics, Institute of Biotechnology, Technische Universität Berlin, 13355 Berlin, Germany.
authors.forename: Juri
authors.initials: J
authors.lastname: Rappsilber
authors.affiliation: Institut Laue Langevin, 71 Avenue des Martyrs, F-38042 Grenoble, France.|CNRS, Institut de Biologie Structurale, F-38044 Grenoble, France.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Zaccai
authors.affiliation: European Molecular Biology Laboratory, Grenoble Outstation, 71 Avenue des Martyrs, 38042 Grenoble, France.|School of Biochemistry, University of Bristol, BS8 1TD, United Kingdom.
authors.forename: Imre
authors.initials: I
authors.lastname: Berger
authors.affiliation: School of Biochemistry, University of Bristol, BS8 1TD, United Kingdom.
authors.forename: Ian
authors.initials: I
authors.lastname: Collinson
authors.affiliation: European Molecular Biology Laboratory, Grenoble Outstation, 71 Avenue des Martyrs, 38042 Grenoble, France.|School of Biochemistry, University of Bristol, BS8 1TD, United Kingdom.
authors.forename: Christiane
authors.initials: C
authors.lastname: Schaffitzel
mesh_terms: D001665:Binding Sites; D003001:Cloning, Molecular; D020285:Cryoelectron Microscopy; D004926:Escherichia coli / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D005822:Genetic Vectors / Q000737:chemistry / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D063747:Methanocaldococcus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D033363:Neutron Diffraction; D011485:Protein Binding; D000072756:Protein Conformation, alpha-Helical; D000072757:Protein Conformation, beta-Strand; D054730:Protein Interaction Domains and Motifs; D021381:Protein Transport; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000069816:SEC Translocation Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D053838:Scattering, Small Angle; D040681:Structural Homology, Protein; D013379:Substrate Specificity; D016963:Thermus thermophilus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D011994:Recombinant Proteins; D000069816:SEC Translocation Channels; C499394:SecD protein, E coli; C057841:SecY protein, E coli; C412443:YIDC protein, E coli