title: Role of the Escherichia coli Tat pathway in outer membrane integrity.
abstract: The Escherichia coli Tat system serves to export folded proteins harbouring an N-terminal twin-arginine signal peptide across the cytoplasmic membrane. Previous work has demonstrated that strains mutated in genes encoding essential Tat pathway components are highly defective in the integrity of their cell envelope. Here, we report the isolation, by transposon mutagenesis, of tat mutant strains that have their outer membrane integrity restored. This outer membrane repair of the tat mutant arises as a result of upregulation of the amiB gene, which encodes a cell wall amidase. Overexpression of the genes encoding the two additional amidases, amiA and amiC, does not compensate for the outer membrane defect of the tatC strain. Analysis of the amiA and amiC coding sequences indicates that the proteins may be synthesized with plausible twin-arginine signal sequences, and we demonstrate that they are translocated to the periplasm by the Tat pathway. A Tat+ strain that has mislocalized AmiA and AmiC proteins because of deletion of their signal peptides displays an identical defective cell envelope phenotype. The presence of genes encoding amidases with twin-arginine signal sequences in the genomes of other Gram-negative bacteria suggests that a similar cell envelope defect may be a common feature of tat mutant strains.
authors.affiliation: Department of Molecular Microbiology, John Innes Centre, Norwich NR4 7UH, UK.
authors.forename: Bérengère
authors.initials: B
authors.lastname: Ize
authors.forename: Nicola R
authors.initials: NR
authors.lastname: Stanley
authors.forename: Grant
authors.initials: G
authors.lastname: Buchanan
authors.forename: Tracy
authors.initials: T
authors.lastname: Palmer
mesh_terms: D000581:Amidohydrolases / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D001483:Base Sequence; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism; D004251:DNA Transposable Elements; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009154:Mutation; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology
chemical_list: D004251:DNA Transposable Elements; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; C408585:twin-arginine translocase complex, E coli; D012967:Sodium Dodecyl Sulfate; D000581:Amidohydrolases