title: Subunit organization in the TatA complex of the twin arginine protein translocase: a site-directed EPR spin labeling study.
abstract: The Tat system is used to transport folded proteins across the cytoplasmic membrane in bacteria and archaea and across the thylakoid membrane of plant chloroplasts. Multimers of the integral membrane TatA protein are thought to form the protein-conducting element of the Tat pathway. Nitroxide radicals were introduced at selected positions within the transmembrane helix of Escherichia coli TatA and used to probe the structure of detergent-solubilized TatA complexes by EPR spectroscopy. A comparison of spin label mobilities allowed classification of individual residues as buried within the TatA complex or exposed at the surface and suggested that residues Ile(12) and Val(14) are involved in interactions between helices. Analysis of inter-spin distances suggested that the transmembrane helices of TatA subunits are arranged as a single-walled ring containing a contact interface between Ile(12) on one subunit and Val(14) on an adjacent subunit. Experiments in which labeled and unlabeled TatA samples were mixed demonstrate that TatA subunits are exchanged between TatA complexes. This observation is consistent with the TatA dynamic polymerization model for the mechanism of Tat transport.
authors.affiliation: School of Chemistry, University of East Anglia, Norwich, Norfolk NR4 7TJ, UK.
authors.forename: Gaye F
authors.initials: GF
authors.lastname: White
authors.forename: Sonya M
authors.initials: SM
authors.lastname: Schermann
authors.forename: Justin
authors.initials: J
authors.lastname: Bradley
authors.forename: Andrew
authors.initials: A
authors.lastname: Roberts
authors.forename: Nicholas P
authors.initials: NP
authors.lastname: Greene
authors.forename: Ben C
authors.initials: BC
authors.lastname: Berks
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Thomson
mesh_terms: D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010957:Plasmids; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013113:Spin Labels
chemical_list: D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D021122:Protein Subunits; D013113:Spin Labels; C408585:twin-arginine translocase complex, E coli