title: SecA supports a constant rate of preprotein translocation.
abstract: In Escherichia coli, secretory proteins (preproteins) are translocated across the cytoplasmic membrane by the Sec system composed of a protein-conducting channel, SecYEG, and an ATP-dependent motor protein, SecA. After binding of the preprotein to SecYEG-bound SecA, cycles of ATP binding and hydrolysis by SecA are thought to drive the stepwise translocation of the preprotein across the membrane. To address how the length of a preprotein substrate affects the SecA-driven translocation process, we constructed derivatives of the precursor of the outer membrane protein A (proOmpA) with 2, 4, 6, and 8 in-tandem repeats of the periplasmic domain. With increasing polypeptide length, an increasing delay in the time before full-length translocation was observed, but the translocation rate expressed as amino acid translocation per minute remained constant. These data indicate that in the ATP-dependent reaction, SecA drives a constant rate of preprotein translocation consistent with a stepping mechanism of translocation.
authors.affiliation: Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute and the Materials Science Centre Plus, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands.
authors.forename: Danuta
authors.initials: D
authors.lastname: Tomkiewicz
authors.forename: Nico
authors.initials: N
authors.lastname: Nouwen
authors.forename: Ruud
authors.initials: R
authors.lastname: van Leeuwen
authors.forename: Sander
authors.initials: S
authors.lastname: Tans
authors.forename: Arnold J M
authors.initials: AJ
authors.lastname: Driessen
mesh_terms: D000251:Adenosine Triphosphatases / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000378:metabolism; D001426:Bacterial Proteins / Q000502:physiology*; D006868:Hydrolysis; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000502:physiology*; D011498:Protein Precursors / Q000378:metabolism; D021381:Protein Transport; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
chemical_list: D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; D011498:Protein Precursors; D000069816:SEC Translocation Channels; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins