title: Structural basis for ligand-regulated oligomerization of AraC.
abstract: The crystal structure of the arabinose-binding and dimerization domain of the Escherchia coli gene regulatory protein AraC was determined in the presence and absence of L-arabinose. The 1.5 angstrom structure of the arabinose-bound molecule shows that the protein adopts an unusual fold, binding sugar within a beta barrel and completely burying the arabinose with the amino-terminal arm of the protein. Dimer contacts in the presence of arabinose are mediated by an antiparallel coiled-coil. In the 2.8 angstrom structure of the uncomplexed protein, the amino-terminal arm is disordered, uncovering the sugar-binding pocket and allowing it to serve as an oligomerization interface. The ligand-gated oligomerization as seen in AraC provides the basis of a plausible mechanism for modulating the protein's DNA-looping properties.
authors.affiliation: Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Soisson
authors.forename: B
authors.initials: B
authors.lastname: MacDougall-Shackleton
authors.forename: R
authors.initials: R
authors.lastname: Schleif
authors.forename: C
authors.initials: C
authors.lastname: Wolberger
mesh_terms: D051777:AraC Transcription Factor; D001089:Arabinose / Q000378:metabolism; D001426:Bacterial Proteins; D001665:Binding Sites; D003460:Crystallization; D018360:Crystallography, X-Ray; D004247:DNA / Q000378:metabolism*; D019281:Dimerization; D006860:Hydrogen Bonding; D008024:Ligands; D008958:Models, Molecular; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012097:Repressor Proteins / Q000737:chemistry* / Q000378:metabolism; D014157:Transcription Factors
chemical_list: D051777:AraC Transcription Factor; D001426:Bacterial Proteins; D008024:Ligands; D012097:Repressor Proteins; D014157:Transcription Factors; D004247:DNA; D001089:Arabinose