title: SecD and SecF are required for the proton electrochemical gradient stimulation of preprotein translocation.
abstract: Mutations in secD and secF show impaired protein translocation across the inner membrane of Escherichia coli. We investigated the effect of SecD and SecF (SecD/F) depletion on preprotein translocation into inverted inner membrane vesicles (IMVs). Both IMVs and cells which were depleted of SecD/F were defective in their ability to maintain a proton electrochemical gradient. The translocation of pre-maltose binding protein (preMBP), which is strongly delta microH+ dependent, showed a 5-fold decreased rate with IMVs lacking SecD/F. In contrast, proteolytic processing of preMBP to MBP by leader peptidase was similar in IMVs containing and lacking SecD/F, consistent with earlier findings that only ATP-dependent translocation is required for the initiation of translocation. In the absence of a delta microH+, with ATP as the sole energy source, preMBP translocation into IMVs which contained or were depleted of SecD/F was identical. Translocation of the precursor of outer membrane protein A (proOmpA) in the presence of subsaturating ATP also required a generated delta microH+ and, under these conditions, proOmpA translocation required SecD/F. With saturating concentrations of ATP, where delta microH+ has little effect on in vitro proOmpA translocation, SecD/F also had little effect on translocation. These results explain why SecD/F effects are precursor protein dependent in vitro.
authors.affiliation: Molecular Biology Institute, University of California, Los Angeles 90024-1570.
authors.forename: R A
authors.initials: RA
authors.lastname: Arkowitz
authors.forename: W
authors.initials: W
authors.lastname: Wickner
mesh_terms: D018528:ATP-Binding Cassette Transporters; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism*; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D004563:Electrochemistry; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D008320:Maltose / Q000378:metabolism*; D058619:Maltose-Binding Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins; D018272:Porins / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism*; D011510:Proteolipids / Q000378:metabolism; D011522:Protons
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D058619:Maltose-Binding Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D018272:Porins; D011498:Protein Precursors; D011510:Proteolipids; D011522:Protons; C499394:SecD protein, E coli; C489583:SecF protein, E coli; C461599:maltose transport system, E coli; C020485:proteoliposomes; C075767:secD protein, Bacteria; C075768:secF protein, Bacteria; D008320:Maltose