title: The isolated complex of the translocase of the outer membrane of mitochondria. Characterization of the cation-selective and voltage-gated preprotein-conducting pore.
abstract: The complex of the translocase mitochondrial outer membrane (TOM), mediates recognition, unfolding, and translocation of preproteins. We have used a combination of biochemical and electrophysiological methods to study the properties of the preprotein-conducting pore of the purified TOM complex. The pore is cation-selective and voltage-gated. It shows three main conductance levels with characteristic slow and fast kinetics transitions to states of lower conductance following application of transmembrane voltages. These electrical properties distinguish it from the mitochondrial voltage-dependent anion channel (porin) and are identical to those of the previously described peptide-sensitive channel. Binding of antibodies to the C terminus of Tom40 on the intermembrane space side of the outer membrane modifies the channel properties and allows determination of the orientation of the channel within the lipid bilayer. Mitochondrial presequence peptides specifically interact with the pore and decrease the ion flow through the channel in a voltage-dependent manner. We propose that the presequence-induced closures of the pore are related to structural alterations of the TOM complex observed during the various stages of preprotein movement across the mitochondrial outer membrane.
authors.affiliation: Institut für Physiologische Chemie, Physikalische Biochemie und Zellbiologie der Universität München, Goethestrasse 33, 80336 Munich, Federal Republic of Germany.
authors.forename: K P
authors.initials: KP
authors.lastname: Künkele
authors.forename: P
authors.initials: P
authors.lastname: Juin
authors.forename: C
authors.initials: C
authors.lastname: Pompa
authors.forename: F E
authors.initials: FE
authors.lastname: Nargang
authors.forename: J P
authors.initials: JP
authors.lastname: Henry
authors.forename: W
authors.initials: W
authors.lastname: Neupert
authors.forename: R
authors.initials: R
authors.lastname: Lill
authors.forename: M
authors.initials: M
authors.lastname: Thieffry
mesh_terms: D001692:Biological Transport; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism*; D002412:Cations / Q000378:metabolism; D016764:Cell Polarity; D004553:Electric Conductivity; D004594:Electrophysiology; D015640:Ion Channel Gating; D007473:Ion Channels / Q000302:isolation & purification / Q000378:metabolism*; D008051:Lipid Bilayers; D008565:Membrane Proteins / Q000276:immunology / Q000378:metabolism; D026901:Membrane Transport Proteins; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D009492:Neurospora crassa / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D002412:Cations; D007473:Ion Channels; D008051:Lipid Bilayers; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D011498:Protein Precursors; D021382:Protein Sorting Signals; D029701:Saccharomyces cerevisiae Proteins; C066555:Tom40 protein, S cerevisiae; C093986:peptide sensitive channel