title: Consensus structural features of purified bacterial TatABC complexes.
abstract: The twin-arginine translocation (Tat) system transports folded proteins across bacterial plasma membranes and the chloroplast thylakoid membrane. Here, we investigate the composition and structural organization of three different purified Tat complexes from Escherichia coli, Salmonella typhimurium and Agrobacterium tumefaciens. First, we demonstrate the functional activity of these Tat systems in vivo, since expression of the tatABC operons from S.typhimurium or A.tumefaciens in an E.coli tat null mutant strain resulted in efficient Tat-dependent export of an E.coli cofactor-containing substrate, TMAO reductase. The three isolated, affinity-tagged Tat complexes comprised TatA, TatB and TatC in each case, demonstrating a strong interaction between these three subunits. Single-particle electron microscopy studies of all three complexes revealed approximately oval-shaped, asymmetric particles with maximal dimensions up to 13 nm. A common feature is a number of stain-excluding densities surrounding more or less central pools of stain, suggesting protein-lined pores or cavities. The characteristics of size variation among the particles suggest a modular form of assembly and/or the recruitment of varying numbers of TatBC/TatA units. Despite low levels of sequence homology, the combined data indicate structural and functional conservation in the Tat systems of these three bacterial species.
authors.affiliation: Department of Biological Sciences, University of Warwick, CV4 7AL, Coventry, UK.
authors.forename: Joanne
authors.initials: J
authors.lastname: Oates
authors.forename: Joanne
authors.initials: J
authors.lastname: Mathers
authors.forename: Dorothea
authors.initials: D
authors.lastname: Mangels
authors.forename: Werner
authors.initials: W
authors.lastname: Kühlbrandt
authors.forename: Colin
authors.initials: C
authors.lastname: Robinson
authors.forename: Kirstin
authors.initials: K
authors.lastname: Model
mesh_terms: D016960:Agrobacterium tumefaciens / Q000737:chemistry / Q000235:genetics; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure; D001483:Base Sequence; D016384:Consensus Sequence; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000648:ultrastructure; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000648:ultrastructure; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D015394:Molecular Structure; D021122:Protein Subunits; D012486:Salmonella typhimurium / Q000737:chemistry / Q000235:genetics; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D021122:Protein Subunits; C408585:twin-arginine translocase complex, E coli