title: The catalytic cycle of the escherichia coli SecA ATPase comprises two distinct preprotein translocation events.
abstract: SecA is the ATP-dependent force generator in the Escherichia coli precursor protein translocation cascade, and is bound at the membrane surface to the integral membrane domain of the preprotein translocase. Preproteins are thought to be translocated in a stepwise manner by nucleotide-dependent cycles of SecA membrane insertion and de-insertion, or as large polypeptide segments by the protonmotive force (Deltap) in the absence of SecA. To determine the step size of a complete ATP- and SecA-dependent catalytic cycle, translocation intermediates of the preprotein proOmpA were generated at limiting SecA translocation ATPase activity. Distinct intermediates were formed, spaced by intervals of approximately 5 kDa. Inhibition of the SecA ATPase by azide trapped SecA in a membrane-inserted state and shifted the step size to 2-2.5 kDa. The latter corresponds to the translocation elicited by binding of non-hydrolysable ATP analogues to SecA, or by the re-binding of partially translocated polypeptide chains by SecA. Therefore, a complete catalytic cycle of the preprotein translocase permits the stepwise translocation of 5 kDa polypeptide segments by two consecutive events, i.e. approximately 2.5 kDa upon binding of the polypeptide by SecA, and another 2.5 kDa upon binding of ATP to SecA.
authors.affiliation: Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands.
authors.forename: J P
authors.initials: JP
authors.lastname: van der Wolk
authors.forename: J G
authors.initials: JG
authors.lastname: de Wit
authors.forename: A J
authors.initials: AJ
authors.lastname: Driessen
mesh_terms: D000251:Adenosine Triphosphatases / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D019943:Amino Acid Substitution; D001386:Azides / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism*; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D002384:Catalysis; D017931:DNA Primers; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D007700:Kinetics; D026901:Membrane Transport Proteins; D016297:Mutagenesis, Site-Directed; D011498:Protein Precursors / Q000378:metabolism*; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
chemical_list: D001386:Azides; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D017931:DNA Primers; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D011498:Protein Precursors; D011994:Recombinant Proteins; D000069816:SEC Translocation Channels; C057184:outer membrane protein A precursor (E coli); D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins