Molecular Basis of BioJ, a Unique Gatekeeper in Bacterial Biotin Synthesis.

Biotin is an indispensable cofactor in the three domains of life. The unusual virulence factor BioJ of Francisella catalyzes the formation of pimeloyl-ACP, an intermediate in biotin synthesis. Here, we report the 1.58 Å crystal structure of BioJ, the enzymatic activity of which is determined with the in vitro reconstituted reaction and biotin bioassay in vivo. Unlike the paradigm BioH, BioJ displays an atypical α/β-hydrolase fold. A structurally conserved catalytic triad (S151, D248, and H278) of BioJ is functionally defined. A proposed model for BioJ catalysis involves two basic residues-rich cavities, of which cavity-1, rather than cavity-2, binds to the ACP moiety of its physiological substrate, pimeloyl-ACP methyl ester. In summary, this finding provides molecular insights into the BioJ gatekeeper of biotin synthesis.