title: Proteolytic processing of Escherichia coli twin-arginine signal peptides by LepB.
abstract: The twin-arginine translocation (Tat) apparatus is a protein targeting system found in the cytoplasmic membranes of many prokaryotes. Substrate proteins of the Tat pathway are synthesised with signal peptides bearing SRRxFLK 'twin-arginine' amino acid motifs. All Tat signal peptides have a common tripartite structure comprising a polar N-terminal region, followed by a hydrophobic region of variable length and a polar C-terminal region. In Escherichia coli, Tat signal peptides are proteolytically cleaved after translocation. The signal peptide C-terminal regions contain conserved AxA motifs, which are possible recognition sequences for leader peptidase I (LepB). In this work, the role of LepB in Tat signal peptide processing was addressed directly. Deliberate repression of lepB expression prevented processing of all Tat substrates tested, including SufI, AmiC, and a TorA-23K reporter protein. In addition, electron microscopy revealed gross defects in cell architecture and membrane integrity following depletion of cellular LepB protein levels.
authors.affiliation: Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK.
authors.forename: Iris
authors.initials: I
authors.lastname: Lüke
authors.forename: Jennifer I
authors.initials: JI
authors.lastname: Handford
authors.forename: Tracy
authors.initials: T
authors.lastname: Palmer
authors.forename: Frank
authors.initials: F
authors.lastname: Sargent
mesh_terms: D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D012697:Serine Endopeptidases; C026515:type I signal peptidase