1: Biochemistry. 2005 Jan 18;44(2):734-43. 

Induced alpha-helix structure in the aryl hydrocarbon receptor transactivation
domain modulates protein-protein interactions.

Watt K, Jess TJ, Kelly SM, Price NC, McEwan IJ.

School of Medical Sciences, Institute of Medical Sciences, University of
Aberdeen, Foresterhill, Aberdeen AB25 2ZD, Scotland, UK.

The aryl hydrocarbon receptor (AhR) is an intracellular receptor protein that
regulates gene transcription in response to both man-made and natural ligands. A
modular transactivaton domain (TAD) has been mapped to the 304 C-terminal amino
acids and consists of acidic, Q-rich, and P/S/T-rich subdomains. We have used
steady-state intrinsic tryptophan fluorescence and circular dichroism
spectroscopy to investigate the conformation of the acidic Q-rich region. The
results reveal that this region of the protein is structurally flexible but
adopts a more folded conformation in the presence of the natural osmolyte
trimethylamine N-oxide (TMAO) and the solvent trifluoroethanol (TFE). In
protein-protein interaction studies, the acidic Q-rich region bound to
components of the general transcription machinery [TATA-binding protein (TBP),
TAF4, and TAF6] as well as the coactivator proteins SRC-1a and TIF2. The binding
site for TBP mapped to the acidic subdomain, while SRC-1a bound preferentially
to the Q-rich sequence. Significantly, the binding of TBP was modulated by
induced folding of the TAD with TMAO. The results indicate that the AhR TAD
makes multiple interactions with the transcriptional machinery and protein
conformation plays a critical role in receptor function. Taken together, these
findings support a role for protein folding in AhR action and suggest possible
mechanisms of receptor-dependent gene activation.

PMID: 15641800 [PubMed - indexed for MEDLINE]


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