title: Lateral opening of the bacterial translocon on ribosome binding and signal peptide insertion.
abstract: Proteins are co-translationally inserted into the bacterial plasma membrane via the SecYEG translocon by lateral release of hydrophobic transmembrane segments into the phospholipid bilayer. The trigger for lateral opening of the translocon is not known. Here we monitor lateral opening by photo-induced electron transfer (PET) between two fluorophores attached to the two SecY helices at the rim of the gate. In the resting translocon, the fluorescence is quenched, consistent with a closed conformation. Ribosome binding to the translocon diminishes PET quenching, indicating opening of the gate. The effect is larger with ribosomes exposing hydrophobic transmembrane segments and vanishes at low temperature. We propose a temperature-dependent dynamic equilibrium between closed and open conformations of the translocon that is shifted towards partially and fully open by ribosome binding and insertion of a hydrophobic peptide, respectively. The combined effects of ribosome and peptide binding allow for co-translational membrane insertion of successive transmembrane segments.
authors.affiliation: Department of Physical Biochemistry, Max-Planck-Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
authors.forename: Yan
authors.initials: Y
authors.lastname: Ge
authors.affiliation: Department of Physical Biochemistry, Max-Planck-Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
authors.forename: Albena
authors.initials: A
authors.lastname: Draycheva
authors.affiliation: Department of Physical Biochemistry, Max-Planck-Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Bornemann
authors.affiliation: Department of Physical Biochemistry, Max-Planck-Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
authors.forename: Marina V
authors.initials: MV
authors.lastname: Rodnina
authors.affiliation: Department of Physical Biochemistry, Max-Planck-Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wintermeyer
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D004579:Electron Transport; D005456:Fluorescent Dyes / Q000737:chemistry; D063747:Methanocaldococcus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D021382:Protein Sorting Signals; D012270:Ribosomes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D005456:Fluorescent Dyes; D021382:Protein Sorting Signals