title: Atomic model of the E. coli membrane-bound protein translocation complex SecYEG.
abstract: The Sec complex forms the core of a conserved machinery transporting proteins across or into membranes. In Escherichia coli SecYEG is active as an oligomer, but the structure predicts that the protein-conducting channel is formed by the monomer. A homology model of the E.coli complex was built using the atomic structure of Methanococcus jannaschii SecYEbeta. Another structure of the membrane-bound dimer was then determined by fitting the homology model to an 8A map of SecYEG determined by electron microscopy. We found that the substrate-binding site of the dimer has opened slightly and the plug domain moved toward the outside. This new position retains the channel in a closed state. These differences partially reflect the movements that have been proposed to occur during channel gating. Further opening of the substrate-binding pocket to bind and release bound substrate and displacement of the plug during secretion, presumably rely on the action of the partner proteins. The contacts arising at the dimer interface in the environment of the lipid bilayer may have activated the assembly.
authors.affiliation: Department of Structural Biology, Max-Planck-Institute of Biophysics, 60439 Frankfurt am Main, Germany.
authors.forename: Mihnea
authors.initials: M
authors.lastname: Bostina
authors.forename: Brigitte
authors.initials: B
authors.lastname: Mohsin
authors.forename: Werner
authors.initials: W
authors.lastname: Kühlbrandt
authors.forename: Ian
authors.initials: I
authors.lastname: Collinson
mesh_terms: D020285:Cryoelectron Microscopy; D019281:Dimerization; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D017017:Methanococcus; D008956:Models, Chemical; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D000069816:SEC Translocation Channels; D040681:Structural Homology, Protein
chemical_list: D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D000069816:SEC Translocation Channels; C065493:SecE protein, E coli; C088616:SecG protein, E coli; C057841:SecY protein, E coli