title: SecA promotes preprotein translocation by undergoing ATP-driven cycles of membrane insertion and deinsertion.
abstract: SecA, the peripheral subunit of E. coli preprotein translocase, alternates between a membrane inserted and a deinserted state as part of the catalytic cycle of preprotein translocation. When SecA is complexed with SecY/E and preprotein, ATP drives a profound conformational change, leading to membrane insertion of a 30 kDa domain of SecA. The inserted domain is protease-inaccessible from the cytosolic side of the membrane, but becomes accessible upon membrane disruption. Concomitant with 30 kDa domain insertion, approximately 20 aminoacyl residues of the preprotein are translocated. Additional ATP, which may be hydrolyzed at the second ATP site of SecA, releases the translocated preprotein and allows the 30 kDa domain to deinsert, whence it can exchange with cytosolic SecA. Thus, SecA is the mobile subunit of an integral membrane transporter, consuming ATP during both the insertion and deinsertion phases of its catalytic cycle while guiding preprotein segments across the membrane.
authors.affiliation: Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755-3844.
authors.forename: A
authors.initials: A
authors.lastname: Economou
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 / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D001692:Biological Transport; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000378:metabolism; D004926:Escherichia coli / Q000502:physiology*; D029968:Escherichia coli Proteins; D008565:Membrane Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D008954:Models, Biological; D011498:Protein Precursors / Q000378:metabolism*; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D011498:Protein Precursors; D000069816:SEC Translocation Channels; C065493:SecE protein, E coli; C057841:SecY protein, E coli; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins