Helen L Bullifent

Publications (2)6.18 Total impact

• Article: Role of trehalose biosynthesis in environmental survival and virulence of Salmonella enterica serovar typhimurium.

  Angela M Howells, Helen L Bullifent, Kam Dhaliwal, Kate Griffin, Arcadio García de Castro, Graeme Frith, Alan Tunnacliffe, Richard W Titball
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  ABSTRACT: The otsA and otsB genes, encoding trehalose-6-phosphate synthase and trehalose-6-phosphate phosphatase respectively, have been isolated from Salmonella enterica serovar typhimurium and nucleotide-sequenced. Induction of trehalose biosynthesis by exposure of bacteria to high osmotic strength resulted in the intracellular accumulation of trehalose. An otsA mutant of S. enterica serovar typhimurium was more susceptible to killing by heat, and grew poorly under conditions of high osmolarity. The wild-type and otsA mutant strains showed similar abilities to colonise spleen tissues after oral dosing of mice. These findings suggest that the otsBA gene products play a role in environmental survival, but not in virulence, of S. enterica serovar typhimurium.
  Research in Microbiology 07/2002; 153(5):281-7. · 2.76 Impact Factor
• Article: The first strain of Clostridium perfringens isolated from an avian source has an alpha-toxin with divergent structural and kinetic properties.

  Neil Justin, Nicola Walker, Helen L Bullifent, Glenn Songer, Dawn M Bueschel, Helen Jost, Claire Naylor, Julie Miller, David S Moss, Richard W Titball, Ajit K Basak
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  ABSTRACT: Clostridium perfringens alpha-toxin is a 370-residue, zinc-dependent, phospholipase C that is the key virulence determinant in gas gangrene. It is also implicated in the pathogenesis of sudden death syndrome in young animals and necrotic enteritis in chickens. Previously characterized alpha-toxins from different strains of C. perfringens are almost identical in sequence and biochemical properties. We describe the cloning, nucleotide sequencing, expression, characterization, and crystal structure of alpha-toxin from an avian strain, SWan C. perfringens (SWCP), which has a large degree of sequence variation and altered substrate specificity compared to these strains. The structure of alpha-toxin from strain CER89L43 has been previously reported in open (active site accessible to substrate) and closed (active site obscured by loop movements) conformations. The SWCP structure is in an open-form conformation, with three zinc ions in the active site. This is the first example of an open form of alpha-toxin crystallizing without the addition of divalent cations to the crystallization buffer, indicating that the protein can retain three zinc ions bound in the active site. The topology of the calcium binding site formed by residues 269, 271, 336, and 337, which is essential for membrane binding, is significantly altered in comparison with both the open and closed alpha-toxin structures. We are able to relate these structural changes to the different substrate specificity and membrane binding properties of this divergent alpha-toxin. This will provide essential information when developing an effective vaccine that will protect against C. perfringens infection in a wide range of domestic livestock.
  Biochemistry 06/2002; 41(20):6253-62. · 3.42 Impact Factor