title: A subset of bacterial inner membrane proteins integrated by the twin-arginine translocase.
abstract: A group of bacterial exported proteins are synthesized with N-terminal signal peptides containing a SRRxFLK 'twin-arginine' amino acid motif. Proteins bearing twin-arginine signal peptides are targeted post-translationally to the twin-arginine translocation (Tat) system which transports folded substrates across the inner membrane. In Escherichia coli, most integral inner membrane proteins are assembled by a co-translational process directed by SRP/FtsY, the SecYEG translocase, and YidC. In this work we define a novel class of integral membrane proteins assembled by a Tat-dependent mechanism. We show that at least five E. coli Tat substrate proteins contain hydrophobic C-terminal transmembrane helices (or 'C-tails'). Fusions between the identified transmembrane C-tails and the exclusively Tat-dependent reporter proteins TorA and SufI render the resultant chimeras membrane-bound. Export-linked signal peptide processing and membrane integration of the chimeras is shown to be both Tat-dependent and YidC-independent. It is proposed that the mechanism of membrane integration of proteins by the Tat system is fundamentally distinct from that employed for other bacterial inner membrane proteins.
authors.affiliation: Centre for Metalloprotein Spectroscopy and Biology, School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, UK.
authors.forename: Kostas
authors.initials: K
authors.lastname: Hatzixanthis
authors.forename: Tracy
authors.initials: T
authors.lastname: Palmer
authors.forename: Frank
authors.initials: F
authors.lastname: Sargent
mesh_terms: D018528:ATP-Binding Cassette Transporters; D019677:Artificial Gene Fusion; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D017930:Genes, Reporter / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D010089:Oxidoreductases, N-Demethylating / Q000235:genetics; D021382:Protein Sorting Signals; D021381:Protein Transport; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D021382:Protein Sorting Signals; D011994:Recombinant Proteins; C473632:SufI protein, E coli; C412443:YIDC protein, E coli; C089849:nikA protein, E coli; C408585:twin-arginine translocase complex, E coli; D010089:Oxidoreductases, N-Demethylating; C023186:trimethylamine dehydrogenase