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

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Botte, Mathieu 
Zaccai, Nathan R 
Nijeholt, Jelger Lycklama À 
Martin, Remy 
Knoops, Kèvin 


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.



Binding Sites, Cloning, Molecular, Cryoelectron Microscopy, Escherichia coli, Escherichia coli Proteins, Gene Expression, Genetic Vectors, Membrane Transport Proteins, Methanocaldococcus, Models, Molecular, Neutron Diffraction, Protein Binding, Protein Conformation, alpha-Helical, Protein Conformation, beta-Strand, Protein Interaction Domains and Motifs, Protein Transport, Recombinant Proteins, SEC Translocation Channels, Scattering, Small Angle, Structural Homology, Protein, Substrate Specificity, Thermus thermophilus

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Springer Science and Business Media LLC