title: The Tat system proofreads FeS protein substrates and directly initiates the disposal of rejected molecules.
abstract: The twin-arginine translocation (Tat) system transports folded proteins across the bacterial plasma membrane, including FeS proteins that receive their cofactors in the cytoplasm. We have studied two Escherichia coli Tat substrates, NrfC and NapG, to examine how, or whether, the system exports only correctly folded and assembled FeS proteins. With NrfC, substitutions in even one of four predicted FeS centres completely block export, indicating an effective proofreading activity. The FeS mutants are rapidly degraded but only if they interact with the Tat translocon; they are stable in a tat deletion strain and equally stable in wild-type cells if the signal peptide twin-arginine motif is removed to block targeting. Basically similar results are obtained with NapG. The Tat apparatus thus proofreads these substrates and directly initiates the turnover of rejected molecules. Turnover of mutated FeS substrates is completely dependent on the TatA/E subunits that are believed to be involved in the late stages of translocation, and we propose that partial translocation triggers substrate turnover within an integrated quality control system for FeS proteins.
authors.affiliation: Department of Biological Sciences, University of Warwick, Coventry, UK.
authors.forename: Cristina F R O
authors.initials: CF
authors.lastname: Matos
authors.forename: Colin
authors.initials: C
authors.lastname: Robinson
authors.forename: Alessandra
authors.initials: A
authors.lastname: Di Cola
mesh_terms: D000595:Amino Acid Sequence; D002265:Carboxylic Ester Hydrolases / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D010088:Oxidoreductases / Q000378:metabolism*; D017510:Protein Folding; D021382:Protein Sorting Signals / Q000502:physiology; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D013379:Substrate Specificity
chemical_list: D029968:Escherichia coli Proteins; D007506:Iron-Sulfur Proteins; D026901:Membrane Transport Proteins; C532425:NrfC protein, E coli; D021382:Protein Sorting Signals; D021122:Protein Subunits; C408585:twin-arginine translocase complex, E coli; D010088:Oxidoreductases; C487715:NapG protein, E coli; D002265:Carboxylic Ester Hydrolases; C075139:ferric enterobactin esterase, E coli