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Mol Microbiol. 2018 Sep;109(5):642-662. doi: 10.1111/mmi.14066. Epub 2018 Jul 24.

Crystal structure and acetylation of BioQ suggests a novel regulatory switch for biotin biosynthesis in Mycobacterium smegmatis.

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Department of Medical Microbiology & Parasitology and Department of General Intensive Care Unit of the Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang, 310058, China.
College of Life Sciences, Fujian Agriculture and Forestry University, Fuzhou, Fujian, 350002, China.
School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, China.
Key Laboratory of Bioorganic Synthesis of Zhejiang Province, College of Biotechnology and Bioengineering, Zhejiang University of Technology, Hangzhou, Zhejiang, 310014, China.
Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, School of Animal Sciences, Zhejiang University, Hangzhou, Zhejiang, 310058, China.


Biotin (vitamin B7), a sulfur-containing fatty acid derivative, is a nutritional virulence factor in certain mycobacterial species. Tight regulation of biotin biosynthesis is important because production of biotin is an energetically expensive process requiring 15-20 equivalents of ATP. The Escherichia coli bifunctional BirA is a prototypical biotin regulatory system. In contrast, mycobacterial BirA is an unusual biotin protein ligase without DNA-binding domain. Recently, we established a novel two-protein paradigm of BioQ-BirA. However, structural and molecular mechanism for BioQ is poorly understood. Here, we report crystal structure of the M. smegmatis BioQ at 1.9 Å resolution. Structure-guided functional mapping defined a seven residues-requiring motif for DNA-binding activity. Western blot and MALDI-TOF MS allowed us to unexpectedly discover that the K47 acetylation activates crosstalking of BioQ to its cognate DNA. More intriguingly, excess of biotin augments the acetylation status of BioQ in M. smegmatis. It seems likely that BioQ acetylation proceeds via a non-enzymatic mechanism. Mutation of this acetylation site K47 in BioQ significantly impairs its regulatory role in vivo. This explains in part (if not all) why BioQ has no detectable requirement of the presumable bio-5'-AMP effecter, which is a well-known ligand for the paradigm E. coli BirA regulator system. Unlike the scenario seen with E. coli carrying a single biotinylated protein, AccB, genome-wide search and Streptavidin blot revealed that no less than seven proteins require the rare post-translational modification, biotinylation in M. smegmatis, validating its physiological demand for biotin at relatively high level. Taken together, our finding defines a novel biotin regulatory machinery by BioQ, posing a possibility that development of new antibiotics targets biotin, the limited nutritional virulence factor in certain pathogenic mycobacterial species.


Mycobacterium smegmatis ; Acetylation; BioQ; Biotin; Crystal structure

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