A Francisella virulence factor catalyses an essential reaction of biotin synthesis

Authors

  • Youjun Feng,

    1. Department of Microbiology, University of Illinois at Urbana-Champaign, IL, USA
    2. Institute of Microbiology, College of Life Science, Zhejiang University, Hangzhou, Zhejiang Province, China
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  • Brooke A. Napier,

    1. Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA, USA
    2. Emory Vaccine Center, Emory University School of Medicine, Atlanta, GA, USA
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  • Miglena Manandhar,

    1. Department of Microbiology, University of Illinois at Urbana-Champaign, IL, USA
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  • Sarah K. Henke,

    1. Department of Microbiology, University of Illinois at Urbana-Champaign, IL, USA
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  • David S. Weiss,

    1. Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA, USA
    2. Emory Vaccine Center, Emory University School of Medicine, Atlanta, GA, USA
    3. Division of Infectious Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, GA, USA
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  • John E. Cronan

    Corresponding author
    1. Department of Microbiology, University of Illinois at Urbana-Champaign, IL, USA
    2. Department of Biochemistry, University of Illinois at Urbana-Champaign, IL, USA
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Summary

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 colibioH 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.

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