title: Dual topology of the Escherichia coli TatA protein.
abstract: The Escherichia coli Tat system has unusual capacity of translocating folded proteins across the cytoplasmic membrane. The TatA protein is the most abundant known Tat component and consists of a transmembrane segment followed by an amphipathic helix and a hydrophilic C terminus. To study the operation mechanism of the Tat apparatus, we analyzed the topology of TatA. Intriguingly, alkaline phosphatase (PhoA)-positive fusions were obtained at positions Gly-38, Lys-40, Asp-51, and Thr-53, which are all located at the cytoplasmic C terminus of the TatA protein. Interestingly, replacing phoA with uidA at Thr-53 led to positive beta-glucuronidase fusion, implying cytoplasmic location of the TatA C terminus. To further determine cellular localization of the TatA C terminus, we deleted the phoA gene and left 46 exogenous residues, including the tobacco etch virus (Tev) protease cleavage site (Tcs) after Thr-53, yielding TatA(T53)::Tcs. Unlike the PhoA and UidA fusions, which abolished the TatA function, the TatA(T53)::Tcs construct was able to restore the growth of tatA mutants on the minimal trimethlyamine N-oxide media. In vitro and in vivo proteolysis assay showed that the Tcs site of TatA(T53)::Tcs was accessible from both the periplasm and cytoplasm, indicating a dual topology of the TatA C terminus. Importantly, growth conditions seemed to influence the protein level of TatA and the cytoplasmic accessibility of the Tcs site of TatA(T53)::Tcs. A function-linked change of the TatA topology is suggested, and its implication in protein transport is discussed.
authors.affiliation: Laboratoire de Chimie Bactérienne, UPR9043, Institut de Biologie Structurale et Microbiologie, CNRS, 31 chemin Joseph Aiguier, F-13402 Marseille cedex 20, France.
authors.forename: Kamila
authors.initials: K
authors.lastname: Gouffi
authors.forename: Fabien
authors.initials: F
authors.lastname: Gérard
authors.forename: Claire-Lise
authors.initials: CL
authors.lastname: Santini
authors.forename: Long-Fei
authors.initials: LF
authors.lastname: Wu
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D017931:DNA Primers; D004926:Escherichia coli / Q000737:chemistry*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D029968:Escherichia coli Proteins