P. Coumailleau et al., DEFINITION OF A MINIMAL DOMAIN OF THE DIOXIN RECEPTOR THAT IS ASSOCIATED WITH HSP90 AND MAINTAINS WILD-TYPE LIGAND-BINDING AFFINITY AND SPECIFICITY, The Journal of biological chemistry, 270(42), 1995, pp. 25291-25300
The dioxin receptor is a cytoplasmic basic helix-loop-helix/Per-Arnt-S
im homology (bHLH/PAS) protein known to bind planar polycyclic ligands
including polycyclic aromatic hydrocarbons, benzoflavones, heterocycl
ic amines, and halogenated aromatic hydrocarbons, e.g. dioxins. Ligand
-induced activation of the dioxin receptor initiates a process whereby
the receptor is transformed into a nuclear transcription factor compl
ex with a specific bHLH/PAS partner protein, Arnt. In analogy to the g
lucocorticoid receptor, the latent dioxin receptor is found associated
with the molecular chaperone hsp90. We have defined and isolated a mi
nimal ligand binding domain of the dioxin receptor from the central PA
S region, comprising of amino acids 230 to 421, and found this domain
to interact with hsp90 in vitro. Expression of the minimal ligand bind
ing domain in wheat germ lysates or bacteria, systems which harbor hsp
90 homologs unable to interact with the glucocorticoid or dioxin recep
tors, resulted in non-ligand binding forms of this minimal 230 to 421
fragment. Importantly, affinity of the minimal ligand binding domain f
or dioxin was similar to the affinity inherent in the full-length diox
in receptor, and a profile of ligand structures which specifically bou
nd the minimal ligand binding domain was found to be conserved between
this domain and the native receptor. These experiments show that the
minimal ligand binding domain maintains the quantitative and qualitati
ve aspects of ligand binding exhibited by the full-length receptor, im
plying that the central ligand binding pocket may exist to accommodate
all classes of specific dioxin receptor ligands, and that this pocket
is critically dependent upon hsp90 for its ligand binding conformatio
n.