Document Detail

Profligate biotin synthesis in α-proteobacteria - a developing or degenerating regulatory system?
MedLine Citation:
PMID:  23387333     Owner:  NLM     Status:  MEDLINE    
Biotin (vitamin H) is a key enzyme cofactor required in all three domains of life. Although this cofactor was discovered over 70 years ago and has long been recognized as an essential nutrient for animals, our knowledge of the strategies bacteria use to sense biotin demand is very limited. The paradigm mechanism is that of Escherichia coli in which BirA protein, the prototypical bi-functional biotin protein ligase, both covalently attaches biotin to the acceptor proteins of central metabolism and represses transcription of the biotin biosynthetic pathway in response to biotin demand. However, in other bacteria the biotin protein ligase lacks a DNA-binding domain which raises the question of how these bacteria regulate the synthesis of biotin, an energetically expensive molecule. A bioinformatic study by Rodionov and Gelfand identified a protein termed BioR in α-proteobacteria and predicted that BioR would have the biotin operon regulatory role that in most other bacteria is fulfilled by the BirA DNA-binding domain. We have now tested this prediction in the plant pathogen Agrobacterium tumefaciens. As predicted the A. tumefaciens biotin protein ligase is a fully functional ligase that has no role in regulation of biotin synthesis whereas BioR represses transcription of the biotin synthesis genes. Moreover, as determined by electrophoretic mobility shift assays, BioR binds the predicted operator site, which is located downstream of the mapped transcription start site. qPCR measurements indicated that deletion of BioR resulted in a c. 15-fold increase of bio operon transcription in the presence of high biotin levels. Effective repression of a plasmid-borne bioB-lacZ reporter was seen only upon the overproduction of BioR. In contrast to E. coli and Bacillus subtilis where biotin synthesis is tightly controlled, A. tumefaciens synthesizes much more biotin than needed for modification of the biotin-requiring enzymes. Protein-bound biotin constitutes only about 0.5% of the total biotin, most of which is found in the culture medium. To the best of our knowledge, A. tumefaciens represents the first example of profligate biotin synthesis by a wild type bacterium.
Youjun Feng; Huimin Zhang; John E Cronan
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Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural     Date:  2013-03-12
Journal Detail:
Title:  Molecular microbiology     Volume:  88     ISSN:  1365-2958     ISO Abbreviation:  Mol. Microbiol.     Publication Date:  2013 Apr 
Date Detail:
Created Date:  2013-03-25     Completed Date:  2013-09-26     Revised Date:  2014-04-17    
Medline Journal Info:
Nlm Unique ID:  8712028     Medline TA:  Mol Microbiol     Country:  England    
Other Details:
Languages:  eng     Pagination:  77-92     Citation Subset:  IM    
Copyright Information:
© 2013 Blackwell Publishing Ltd.
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MeSH Terms
Agrobacterium tumefaciens / genetics,  growth & development,  metabolism*
Amino Acid Sequence
Bacillus subtilis / metabolism
Bacterial Proteins / genetics,  metabolism
Base Sequence
Biotin / biosynthesis*
Carbon-Nitrogen Ligases / chemistry,  metabolism
DNA, Bacterial / metabolism
Escherichia coli / metabolism
Genes, Bacterial / genetics
Membrane Transport Proteins / metabolism
Molecular Sequence Data
Multigene Family / genetics
Operon / genetics
Promoter Regions, Genetic / genetics
Protein Binding / genetics
Repressor Proteins / metabolism
Transcription, Genetic
Grant Support
Reg. No./Substance:
0/Bacterial Proteins; 0/DNA, Bacterial; 0/Ligands; 0/Membrane Transport Proteins; 0/Repressor Proteins; 6SO6U10H04/Biotin; EC 6.3.-/Carbon-Nitrogen Ligases

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