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Sci Rep. 2016 Dec 7;6:38399. doi: 10.1038/srep38399.

A central cavity within the holo-translocon suggests a mechanism for membrane protein insertion.

Author information

1
European Molecular Biology Laboratory, Grenoble Outstation, 71 Avenue des Martyrs, 38042 Grenoble, France.
2
School of Biochemistry, University of Bristol, BS8 1TD, United Kingdom.
3
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.
4
Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, EH9 3JR, United Kingdom.
5
Department of Physics, University of Illinois Urbana Champaign, 3217 Beckman Institute, 405 N Mathews Ave., Urbana, IL 61801, USA.
6
Department of Bioanalytics, Institute of Biotechnology, Technische Universität Berlin, 13355 Berlin, Germany.
7
Institut Laue Langevin, 71 Avenue des Martyrs, F-38042 Grenoble, France.
8
CNRS, Institut de Biologie Structurale, F-38044 Grenoble, France.

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.

PMID:
27924919
PMCID:
PMC5141469
DOI:
10.1038/srep38399
[Indexed for MEDLINE]
Free PMC Article

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