A Francisella virulence factor catalyses an essential reaction of biotin synthesis

Mol Microbiol. 2014 Jan;91(2):300-14. doi: 10.1111/mmi.12460. Epub 2013 Dec 9.

Abstract

We recently identified a gene (FTN_0818) required for Francisella virulence that seemed likely involved in biotin metabolism. However, the molecular function of this virulence determinant was unclear. Here we show that this protein named BioJ is the enzyme of the biotin biosynthesis pathway that determines the chain length of the biotin valeryl side-chain. Expression of bioJ allows growth of an Escherichia coli bioH strain on biotin-free medium, indicating functional equivalence of BioJ to the paradigm pimeloyl-ACP methyl ester carboxyl-esterase, BioH. BioJ was purified to homogeneity, shown to be monomeric and capable of hydrolysis of its physiological substrate methyl pimeloyl-ACP to pimeloyl-ACP, the precursor required to begin formation of the fused heterocyclic rings of biotin. Phylogenetic analyses confirmed that distinct from BioH, BioJ represents a novel subclade of the α/β-hydrolase family. Structure-guided mapping combined with site-directed mutagenesis revealed that the BioJ catalytic triad consists of Ser151, Asp248 and His278, all of which are essential for activity and virulence. The biotin synthesis pathway was reconstituted reaction in vitro and the physiological role of BioJ directly assayed. To the best of our knowledge, these data represent further evidence linking biotin synthesis to bacterial virulence.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Asparagine / metabolism
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Biocatalysis
  • Biotin / biosynthesis*
  • Carboxylesterase / metabolism
  • Catalytic Domain / genetics
  • Female
  • Francisella / enzymology*
  • Francisella / genetics
  • Francisella / pathogenicity*
  • Genes, Essential
  • Gram-Negative Bacterial Infections / microbiology
  • Histidine / metabolism
  • Hydrolases / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Models, Molecular
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Phylogeny
  • Protein Conformation
  • Protein Structure, Secondary
  • Serine / metabolism
  • Virulence Factors / chemistry
  • Virulence Factors / genetics
  • Virulence Factors / metabolism*

Substances

  • Bacterial Proteins
  • Virulence Factors
  • Serine
  • Histidine
  • Biotin
  • Asparagine
  • Hydrolases
  • Carboxylesterase