title: Delta mu H+ and ATP function at different steps of the catalytic cycle of preprotein translocase.
abstract: Preprotein translocation in E. coli requires ATP, the membrane electrochemical potential delta mu H+, and translocase, an enzyme with an ATPase domain (SecA) and the membrane-embedded SecY/E. Studies of translocase and proOmpA binds to the SecA domain. Second, SecA binds ATP. Third, ATP-binding energy permits translocation of approximately 20 residues of proOmpA. Fourth, ATP hydrolysis releases proOmpA. ProOmpA may then rebind to SecA and reenter this cycle, allowing progress through a series of transmembrane intermediates. In the absence of delta mu H+ or association with SecA, proOmpA passes backward through the membrane, but moves forward when either ATP and SecA or a membrane electrochemical potential is supplied. However, in the presence of delta mu H+ (fifth step), proOmpA rapidly completes translocation. delta mu H(+)-driven translocation is blocked by SecA plus nonhydrolyzable ATP analogs, indicating that delta mu H+ drives translocation when ATP and proOmpA are not bound to SecA.
authors.affiliation: Molecular Biology Institute, University of California, Los Angeles 90024-15.
authors.forename: E
authors.initials: E
authors.lastname: Schiebel
authors.forename: A J
authors.initials: AJ
authors.lastname: Driessen
authors.forename: F U
authors.initials: FU
authors.lastname: Hartl
authors.forename: W
authors.initials: W
authors.lastname: Wickner
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D026901:Membrane Transport Proteins; D008954:Models, Biological; D010084:Oxidation-Reduction; D011485:Protein Binding; D011498:Protein Precursors / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D011498:Protein Precursors; D000069816:SEC Translocation Channels; C057184:outer membrane protein A precursor (E coli); D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins