Vivienne Mahon

Publications (5)15.13 Total impact

• Article: Snap denaturation reveals dimerization by AraC-like protein Rns.

  Vivienne Mahon, Robert P Fagan, Stephen G J Smith
  [show abstract] [hide abstract]
  ABSTRACT: Here we show that the Rns regulator of Escherichia coli dimerises in vivo and in vitro. Furthermore, we demonstrate that Rns forms aggregates in vitro and describe a methodology to ameliorate aggregation thus permitting the analysis of Rns by cross-linking.
  Biochimie 05/2012; 94(9):2058-61. · 3.02 Impact Factor
• Article: A novel role for SarX in Staphylococcus epidermidis biofilm regulation.

  Sarah E Rowe, Vivienne Mahon, Stephen G Smith, James P O'Gara
  [show abstract] [hide abstract]
  ABSTRACT: Biofilm production by staphylococci is an important virulence determinant mediated by the icaADBC-encoded polysaccharide intercellular adhesin (PIA) or by surface and extracellular proteins. Deletion of the Staphylococcus accessory regulator sarX significantly reduced biofilm-forming capacity in Staphylococcus epidermidis CSF41498, whereas multicopy sarX complemented the sarX mutant and increased wild-type biofilm production. In Staphylococcus aureus, SarX negatively regulates the accessory gene regulator (Agr) system, which in turn has strain-specific effects on biofilm regulation. Here we found that purified S. epidermidis SarX protein bound specifically to the agr P3 promoter. However RT-PCR analysis revealed that both mutation of sarX and multicopy sarX activated RNAIII transcription, making it difficult to correlate sarX-mediated biofilm regulation with altered agr activity. In contrast, RT-PCR and immunoblot analysis revealed that icaA transcription and PIA expression were decreased in the sarX mutant, whereas multicopy sarX increased ica and PIA expression. Furthermore, multicopy sarX did not promote biofilms in an icaC mutant. Finally, purified SarX protein bound specifically to the ica operon promoter. Taken together, these data reveal that the S. epidermidis SarX protein regulates the transcriptional activity of the agr and ica loci and controls the biofilm phenotype, primarily by regulating icaADBC transcription and PIA production.
  Microbiology 02/2011; 157(Pt 4):1042-9. · 3.06 Impact Factor
• Source

  Available from: Ian R Henderson

  Article: A commensal gone bad: complete genome sequence of the prototypical enterotoxigenic Escherichia coli strain H10407.

  Lisa C Crossman, Roy R Chaudhuri, Scott A Beatson, Timothy J Wells, Mickael Desvaux, Adam F Cunningham, Nicola K Petty, Vivienne Mahon, Carl Brinkley, Jon L Hobman, Stephen J Savarino, Susan M Turner, Mark J Pallen, Charles W Penn, Julian Parkhill, A Keith Turner, Timothy J Johnson, Nicholas R Thomson, Stephen G J Smith, Ian R Henderson
  [show abstract] [hide abstract]
  ABSTRACT: In most cases, Escherichia coli exists as a harmless commensal organism, but it may on occasion cause intestinal and/or extraintestinal disease. Enterotoxigenic E. coli (ETEC) is the predominant cause of E. coli-mediated diarrhea in the developing world and is responsible for a significant portion of pediatric deaths. In this study, we determined the complete genomic sequence of E. coli H10407, a prototypical strain of enterotoxigenic E. coli, which reproducibly elicits diarrhea in human volunteer studies. We performed genomic and phylogenetic comparisons with other E. coli strains, revealing that the chromosome is closely related to that of the nonpathogenic commensal strain E. coli HS and to those of the laboratory strains E. coli K-12 and C. Furthermore, these analyses demonstrated that there were no chromosomally encoded factors unique to any sequenced ETEC strains. Comparison of the E. coli H10407 plasmids with those from several ETEC strains revealed that the plasmids had a mosaic structure but that several loci were conserved among ETEC strains. This study provides a genetic context for the vast amount of experimental and epidemiological data that have been published.
  Journal of bacteriology 11/2010; 192(21):5822-31. · 3.94 Impact Factor
• Article: Mutagenesis of the Rns regulator of enterotoxigenic Escherichia coli reveals roles for a linker sequence and two helix-turn-helix motifs.

  Vivienne Mahon, Cyril J Smyth, Stephen G J Smith
  [show abstract] [hide abstract]
  ABSTRACT: The pathogenesis of diarrhoeal disease due to human enterotoxigenic Escherichia coli absolutely requires the expression of fimbriae. The expression of CS1 fimbriae is positively regulated by the AraC-like protein Rns. AraC-like proteins are DNA-binding proteins that typically contain two helix-turn-helix (HTH) motifs. A program of pentapeptide insertion mutagenesis of the Rns protein was performed, and this revealed that both HTH motifs are required by Rns to positively regulate CS1 fimbrial gene expression. Intriguingly, a pentapeptide insertion after amino acid C102 reduced the ability of Rns to transactivate CS1 fimbrial expression. The structure of Rns in this vicinity (NACRS) was predicted to be disordered and thus might act as a flexible linker. This hypothesis was confirmed by deletion of this amino acid sequence from the Rns protein; a truncated protein that lacked this sequence was no longer functional. Strikingly, this sequence could be functionally substituted in vivo and in vitro by a flexible seven amino acid sequence from another E. coli AraC-like protein RhaS. Our data indicate that HTH motifs and a flexible sequence are required by Rns for maximal activation of fimbrial gene expression.
  Microbiology 09/2010; 156(Pt 9):2796-806. · 3.06 Impact Factor
• Article: A molecular Swiss army knife: OmpA structure, function and expression.

  Stephen G J Smith, Vivienne Mahon, Matthew A Lambert, Robert P Fagan
  [show abstract] [hide abstract]
  ABSTRACT: The OmpA outer membrane protein of Escherichia coli and other enterobacteria is a multifaceted protein. This protein is expressed to very high levels and ompA is tightly regulated at the posttranscriptional level. It can function as an adhesin and invasin, participate in biofilm formation, act as both an immune target and evasin, and serves as a receptor for several bacteriophages. Many of these properties are due to four short protein loops that emanate from the protein to the outside of the cell. Herein it is described how the structure of this protein relates to its many functions.
  FEMS Microbiology Letters 09/2007; 273(1):1-11. · 2.04 Impact Factor