title: Transmembrane insertion of twin-arginine signal peptides is driven by TatC and regulated by TatB.
abstract: The twin-arginine translocation (Tat) pathway of bacteria and plant chloroplasts mediates the transmembrane transport of folded proteins, which harbour signal sequences with a conserved twin-arginine motif. Many Tat translocases comprise the three membrane proteins TatA, TatB and TatC. TatC was previously shown to be involved in recognizing twin-arginine signal peptides. Here we show that beyond recognition, TatC mediates the transmembrane insertion of a twin-arginine signal sequence, thereby translocating the signal sequence cleavage site across the bilayer. In the absence of TatB, this can lead to the removal of the signal sequence even from a translocation-incompetent substrate. Hence interaction of twin-arginine signal peptides with TatB counteracts their premature cleavage uncoupled from translocation. This capacity of TatB is not shared by the homologous TatA protein. Collectively our results suggest that TatC is an insertase for twin-arginine signal peptides and that translocation-proficient signal sequence recognition requires the concerted action of TatC and TatB.
authors.affiliation: Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, Stefan-Meier-Strasse 17 D-79104 Freiburg, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Fröbel
authors.forename: Patrick
authors.initials: P
authors.lastname: Rose
authors.forename: Frank
authors.initials: F
authors.lastname: Lausberg
authors.forename: Anne-Sophie
authors.initials: AS
authors.lastname: Blümmel
authors.forename: Roland
authors.initials: R
authors.lastname: Freudl
authors.forename: Matthias
authors.initials: M
authors.lastname: Müller
mesh_terms: D004926:Escherichia coli / Q000378:metabolism / Q000502:physiology; D029968:Escherichia coli Proteins / Q000502:physiology*; D026901:Membrane Transport Proteins / Q000502:physiology*; D021382:Protein Sorting Signals / Q000502:physiology*
chemical_list: D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D021382:Protein Sorting Signals; C473116:TatB protein, E coli; C461379:TatC protein, E coli; C408585:twin-arginine translocase complex, E coli