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Structural Basis for Ligand-Regulated Oligomerization of AraC

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Science  18 Apr 1997:
Vol. 276, Issue 5311, pp. 421-425
DOI: 10.1126/science.276.5311.421

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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 β 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.

  • * To whom correspondence should be addressed. E-mail: bob{at}gene.bio.jhu.edu (R.S) or cynthia{at}groucho.med.jhmi.edu (C.W.)

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