Journal
NUCLEIC ACIDS RESEARCH
Volume 41, Issue 3, Pages 1998-2008Publisher
OXFORD UNIV PRESS
DOI: 10.1093/nar/gks1207
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Funding
- M.D. Anderson Trust Fellowship
- National Institutes of Health [GM068453]
- NIH (SIG program)
- UNMC Program of Excellence (POE)
- Nebraska Research Initiative (NRI)
- Duke University
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Escherichia coli can rapidly switch to the metabolism of L-arabinose and D-xylose in the absence of its preferred carbon source, glucose, in a process called carbon catabolite repression. Transcription of the genes required for L-arabinose and D-xylose consumption is regulated by the sugar-responsive transcription factors, AraC and XylR. E. coli represents a promising candidate for biofuel production through the metabolism of hemicellulose, which is composed of D-xylose and L-arabinose. Understanding the L-arabinose/D-xylose regulatory network is key for such biocatalyst development. Unlike AraC, which is a well-studied protein, little is known about XylR. To gain insight into XylR function, we performed biochemical and structural studies. XylR contains a C-terminal AraC-like domain. However, its N-terminal D-xylose-binding domain contains a periplasmic-binding protein (PBP) fold with structural homology to LacI/GalR transcription regulators. Like LacI/GalR proteins, the XylR PBP domain mediates dimerization. However, unlike LacI/GalR proteins, which dimerize in a parallel, side-to-side manner, XylR PBP dimers are antiparallel. Strikingly, D-xylose binding to this domain results in a helix to strand transition at the dimer interface that reorients both DNA-binding domains, allowing them to bind and loop distant operator sites. Thus, the combined data reveal the ligand-induced activation mechanism of a new family of DNA-binding proteins.
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