title: TatBC-independent TatA/Tat substrate interactions contribute to transport efficiency.
abstract: The Tat system can transport folded, signal peptide-containing proteins (Tat substrates) across energized membranes of prokaryotes and plant plastids. A twin-arginine motif in the signal peptide of Tat substrates is recognized by TatC-containing complexes, and TatA permits the membrane passage. Often, as in the model Tat systems of Escherichia coli and plant plastids, a third component - TatB - is involved that resembles TatA but has a higher affinity to TatC. It is not known why most TatA dissociates from TatBC complexes in vivo and distributes more evenly in the membrane. Here we show a TatBC-independent substrate-binding to TatA from Escherichia coli, and we provide evidence that this binding enhances Tat transport. First hints came from in vivo cross-linking data, which could be confirmed by affinity co-purification of TatA with the natural Tat substrates HiPIP and NrfC. Two positions on the surface of HiPIP could be identified that are important for the TatA interaction and transport efficiency, indicating physiological relevance of the interaction. Distributed TatA thus may serve to accompany membrane-interacting Tat substrates to the few TatBC spots in the cells.
authors.affiliation: Institute of Microbiology, Leibniz Universität Hannover, Schneiderberg 50, 30167, Hannover, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Taubert
authors.affiliation: Institute of Microbiology, Leibniz Universität Hannover, Schneiderberg 50, 30167, Hannover, Germany.
authors.forename: Bo
authors.initials: B
authors.lastname: Hou
authors.affiliation: Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany.
authors.forename: H Jelger
authors.initials: HJ
authors.lastname: Risselada
authors.affiliation: Institute of Microbiology, Leibniz Universität Hannover, Schneiderberg 50, 30167, Hannover, Germany.
authors.forename: Denise
authors.initials: D
authors.lastname: Mehner
authors.affiliation: Helmholtz Centre of Infection Research, Inhoffenstraße 7, 38124, Braunschweig, Germany.
authors.forename: Heinrich
authors.initials: H
authors.lastname: Lünsdorf
authors.affiliation: Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany.
authors.forename: Helmut
authors.initials: H
authors.lastname: Grubmüller
authors.affiliation: Institute of Microbiology, Leibniz Universität Hannover, Schneiderberg 50, 30167, Hannover, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Brüser
mesh_terms: D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology
chemical_list: D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; C499697:TatA protein, E coli; C473116:TatB protein, E coli; C461379:TatC protein, E coli