title: Structure of the SecY complex unlocked by a preprotein mimic.
abstract: The Sec complex forms the core of a conserved machinery coordinating the passage of proteins across or into biological membranes. The bacterial complex SecYEG interacts with the ATPase SecA or translating ribosomes to translocate secretory and membrane proteins accordingly. A truncated preprotein competes with the physiological full-length substrate and primes the protein-channel complex for transport. We have employed electron cryomicroscopy of two-dimensional crystals to determine the structure of the complex unlocked by the preprotein. Its visualization in the native environment of the membrane preserves the active arrangement of SecYEG dimers, in which only one of the two channels is occupied by the polypeptide substrate. The signal sequence could be identified along with the corresponding conformational changes in SecY, including relocation of transmembrane segments 2b and 7 as well as the plug, which presumably then promote channel opening. Therefore, we propose that the structure describes the translocon unlocked by preprotein and poised for protein translocation.
authors.affiliation: Max Planck Institute of Biophysics, Department of Structural Biology, Max-von-Laue-Straße 3, D-60438 Frankfurt am Main, Germany.
authors.forename: Dilem
authors.initials: D
authors.lastname: Hizlan
authors.forename: Alice
authors.initials: A
authors.lastname: Robson
authors.forename: Sarah
authors.initials: S
authors.lastname: Whitehouse
authors.forename: Vicki A
authors.initials: VA
authors.lastname: Gold
authors.forename: Janet
authors.initials: J
authors.lastname: Vonck
authors.forename: Deryck
authors.initials: D
authors.lastname: Mills
authors.forename: Werner
authors.initials: W
authors.lastname: Kühlbrandt
authors.forename: Ian
authors.initials: I
authors.lastname: Collinson
mesh_terms: D000595:Amino Acid Sequence; D003460:Crystallization; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism; D011485:Protein Binding; D055503:Protein Multimerization; D011498:Protein Precursors / Q000378:metabolism*; D021382:Protein Sorting Signals; D017433:Protein Structure, Secondary; D021381:Protein Transport; D000069816:SEC Translocation Channels; D015533:Transcriptional Activation / Q000235:genetics
chemical_list: D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D010455:Peptides; D011498:Protein Precursors; D021382:Protein Sorting Signals; D000069816:SEC Translocation Channels; C065493:SecE protein, E coli; C088616:SecG protein, E coli; C057841:SecY protein, E coli