title: Ion conductivity of the bacterial translocation channel SecYEG engaged in translocation.
abstract: While engaged in protein transport, the bacterial translocon SecYEG must maintain the membrane barrier to small ions. The preservation of the proton motif force was attributed to (i) cation exclusion, (ii) engulfment of the nascent chain by the hydrophobic pore ring, and (iii) a half-helix partly plugging the channel. In contrast, we show here that preservation of the proton motif force is due to a voltage-driven conformational change. Preprotein or signal peptide binding to the purified and reconstituted SecYEG results in large cation and anion conductivities only when the membrane potential is small. Physiological values of membrane potential close the activated channel. This voltage-dependent closure is not dependent on the presence of the plug domain and is not affected by mutation of 3 of the 6 constriction residues to glycines. Cellular ion homeostasis is not challenged by the small remaining leak conductance.
authors.affiliation: From the Institute of Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, A-4020 Linz, Austria.
authors.forename: Denis G
authors.initials: DG
authors.lastname: Knyazev
authors.affiliation: From the Institute of Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, A-4020 Linz, Austria.
authors.forename: Lukas
authors.initials: L
authors.lastname: Winter
authors.affiliation: From the Institute of Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, A-4020 Linz, Austria.
authors.forename: Benedikt W
authors.initials: BW
authors.lastname: Bauer
authors.affiliation: From the Institute of Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, A-4020 Linz, Austria.
authors.forename: Christine
authors.initials: C
authors.lastname: Siligan
authors.affiliation: From the Institute of Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, A-4020 Linz, Austria peter.pohl@jku.at.
authors.forename: Peter
authors.initials: P
authors.lastname: Pohl
mesh_terms: D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D008051:Lipid Bilayers; D021381:Protein Transport; D000069816:SEC Translocation Channels
chemical_list: D029968:Escherichia coli Proteins; D008051:Lipid Bilayers; D000069816:SEC Translocation Channels
keywords: Electrophysiology; Lipid Bilayer; Membrane Transport; Membrane Transporter Reconstitution; Protein Translocation; Proton Motive Force