title: Unusual genetic organization of a functional type I protein secretion system in Neisseria meningitidis.
abstract: Proteins secreted by Neisseria meningitidis are thought to play important roles in the pathogenesis of meningococcal disease. These proteins include the iron-repressible repeat-in-toxin (RTX) exoprotein FrpC. Related proteins in other pathogens are secreted via a type I secretion system (TOSS), but such a system has not been demonstrated in N. meningitidis. An in silico search of the group B meningococcal genome suggested the presence of a uniquely organized TOSS. Genes encoding homologs of the Escherichia coli HlyB (ATP-binding), HlyD (membrane fusion), and TolC (outer membrane channel) proteins were identified. In contrast to the cistronic organization of the secretion genes in most other rtx operons, the hlyD and tolC genes were adjacent but unlinked to hlyB; neither locus was part of an operon containing genes encoding putative TOSS substrates. Both loci were flanked by genes normally associated with mobile genetic elements. The three genes were shown to be expressed independently. Mutation at either locus resulted in an inability to secrete FrpC and a related protein, here called FrpC2. Successful complementation of these mutations at an ectopic site confirmed the observed phenotypes were caused by loss of function of the putative TOSS genes. We show that genes scattered in the meningococcal genome encode a functional TOSS required for secretion of the meningococcal RTX proteins.
authors.affiliation: Division of Microbiology and Infectious Diseases, Queens Medical Centre, Nottingham NG7 2UH, United Kingdom. karl.wooldridge@nottingham.ac.uk
authors.forename: Karl G
authors.initials: KG
authors.lastname: Wooldridge
authors.forename: Murat
authors.initials: M
authors.lastname: Kizil
authors.forename: Damien B
authors.initials: DB
authors.lastname: Wells
authors.forename: Dlawer A A
authors.initials: DA
authors.lastname: Ala'aldeen
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics* / Q000502:physiology; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D022761:Gene Transfer, Horizontal; D006460:Hemolysin Proteins; D007501:Iron / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D009344:Neisseria gonorrhoeae / Q000235:genetics; D042806:Neisseria lactamica / Q000235:genetics; D009345:Neisseria meningitidis / Q000235:genetics* / Q000502:physiology; D011506:Proteins / Q000378:metabolism*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D006460:Hemolysin Proteins; C504430:HlyD protein, Neisseria meningitidis; C050837:Hlyb protein, Bacteria; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D011506:Proteins; C083530:frpC protein, Neisseria meningitidis; C073126:tolC protein, E coli; D007501:Iron