title: Determining the conductance of the SecY protein translocation channel for small molecules.
abstract: The channel formed by the SecY complex must maintain the membrane barrier for ions and other small molecules during the translocation of membrane or secretory proteins. We have tested the permeability of the channel by using planar bilayers containing reconstituted purified E. coli SecY complex. Wild-type SecY complex did not show any conductance for ions or water. Deletion of the "plug," a short helix normally located in the center of the SecY complex, or modification of a cysteine introduced into the plug resulted in transient channel openings; a similar effect was seen with a mutation in the pore ring, a constriction in the center of the channel. Permanent channel opening occurred when the plug was moved out of the way by disulfide-bridge formation. These data show that the resting channel on its own forms a barrier for small molecules, with both the pore ring and the plug required for the seal; channel opening requires movement of the plug.
authors.affiliation: Institut fuer Biophysik, Johannes Kepler Universitaet Linz, Linz, Austria.
authors.forename: Sapar M
authors.initials: SM
authors.lastname: Saparov
authors.forename: Karl
authors.initials: K
authors.lastname: Erlandson
authors.forename: Kurt
authors.initials: K
authors.lastname: Cannon
authors.forename: Julia
authors.initials: J
authors.lastname: Schaletzky
authors.forename: Sol
authors.initials: S
authors.lastname: Schulman
authors.forename: Tom A
authors.initials: TA
authors.lastname: Rapoport
authors.forename: Peter
authors.initials: P
authors.lastname: Pohl
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D001692:Biological Transport; D002462:Cell Membrane / Q000648:ultrastructure; D002463:Cell Membrane Permeability; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D008051:Lipid Bilayers; D009154:Mutation; D021381:Protein Transport; D000069816:SEC Translocation Channels; D017384:Sequence Deletion
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008051:Lipid Bilayers; D000069816:SEC Translocation Channels; C057841:SecY protein, E coli