title: Mutations in the consensus ATP-binding sites of XcpR and PilB eliminate extracellular protein secretion and pilus biogenesis in Pseudomonas aeruginosa.
abstract: The process of extracellular secretion in Pseudomonas aeruginosa requires specialized machinery which is widely distributed among bacteria that actively secrete proteins to the extracellular medium. One of the components of this machinery is the product of the xcpR gene, which is homologous to pilB, a gene encoding a protein essential for the biogenesis of type IV pili. Both XcpR and PilB are characterized by the presence of a conserved ATP-binding motif (Walker sequence). The codons of highly conserved glycine residues within the Walker sequences of xcpR and pilB were altered to encode a serine, and the effects of these substitutions were examined. Bacteria expressing mutant XcpR or PilB were unable to secrete exotoxin A or assemble pili, respectively. In addition, high-level expression of mutant XcpR in wild-type P. aeruginosa led to a pleiotropic extracellular secretion defect, resulting in the periplasmic accumulation of enzymes that are normally secreted from the cell. These studies show that the putative ATP-binding sites of XcpR and PilB are essential for their functions in protein secretion and assembly of pili, respectively. Moreover, the observed dominant negative phenotype of mutant XcpR suggests that this protein functions as a multimer or, alternatively, interacts with another essential component of the extracellular protein secretion machinery.
authors.affiliation: Department of Microbiology, School of Medicine, University of Washington, Seattle 98195.
authors.forename: L R
authors.initials: LR
authors.lastname: Turner
authors.forename: J C
authors.initials: JC
authors.lastname: Lara
authors.forename: D N
authors.initials: DN
authors.lastname: Nunn
authors.forename: S
authors.initials: S
authors.lastname: Lory
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D002451:Cell Compartmentation; D016384:Consensus Sequence / Q000235:genetics; D010861:Fimbriae, Bacterial / Q000378:metabolism* / Q000648:ultrastructure; D005998:Glycine / Q000235:genetics; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010088:Oxidoreductases; D017105:Pseudomonas Phages / Q000254:growth & development; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D012694:Serine / Q000235:genetics; D014170:Transformation, Genetic; D001618:beta-Lactamases / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; C082573:xcpR protein, Pseudomonas aeruginosa; D012694:Serine; D000255:Adenosine Triphosphate; D010088:Oxidoreductases; C068255:pilB protein, Bacteria; D000469:Alkaline Phosphatase; D001618:beta-Lactamases; D005998:Glycine