title: Distinct catalytic roles of the SecYE, SecG and SecDFyajC subunits of preprotein translocase holoenzyme.
abstract: Escherichia coli preprotein translocase contains a membrane-embedded trimeric complex of SecY, SecE and SecG (SecYEG) and the peripheral SecA protein. SecYE is the conserved functional 'core' of the SecYEG complex. Although sufficient to provide sites for high-affinity binding and membrane insertion of SecA, and for its activation as a preprotein-dependent ATPase, SecYE has only very low capacity to support translocation. The proteins encoded by the secD operon--SecD, SecF and YajC--also form an integral membrane heterotrimeric complex (SecDFyajC). Physical and functional studies show that these two trimeric complexes are associated to form SecYEGDFyajC, the hexameric integral membrane domain of the preprotein translocase 'holoenzyme'. Either SecG or SecDFyajC can support the translocation activity of SecYE by facilitating the ATP-driven cycle of SecA membrane insertion and de-insertion at different stages of the translocation reaction. Our findings show that each of the prokaryote-specific subunits (SecA, SecG and SecDFyajC) function together to promote preprotein movement at the SecYE core of the translocase.
authors.affiliation: Dartmouth Medical School, Department of Biochemistry, Hanover, NH 03755, USA.
authors.forename: F
authors.initials: F
authors.lastname: Duong
authors.forename: W
authors.initials: W
authors.lastname: Wickner
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D003067:Coenzymes / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D006868:Hydrolysis; D046911:Macromolecular Substances; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D011233:Precipitin Tests; D011485:Protein Binding; D011498:Protein Precursors / Q000378:metabolism*; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
chemical_list: D001426:Bacterial Proteins; D003067:Coenzymes; D029968:Escherichia coli Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D011498:Protein Precursors; D000069816:SEC Translocation Channels; C499394:SecD protein, E coli; C065493:SecE protein, E coli; C489583:SecF protein, E coli; C088616:SecG protein, E coli; C057841:SecY protein, E coli; C075767:secD protein, Bacteria; C075768:secF protein, Bacteria; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins