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

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

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

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

Substances

  • Escherichia coli Proteins
  • Membrane Transport Proteins
  • Recombinant Proteins
  • SEC Translocation Channels
  • SecD protein, E coli
  • SecY protein, E coli
  • YIDC protein, E coli