Aryl hydrocarbon (Ah) receptor DNA-binding activity. Sequence specificity and Zn2+ requirement

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• The aryl hydrocarbon (Ah) receptor regulates gene expression, including the cytochrome P-450c (CYP1A1) gene, by binding to xenobiotic response elements.
• The precise molecular mechanisms and cofactor requirements for Ah receptor DNA binding are not fully elucidated.

Purpose of the Study:

• To investigate the role of metal ions in the DNA-binding activity of the aryl hydrocarbon (Ah) receptor.
• To map the specific interactions between the Ah receptor and its DNA response element (XRE1).

Main Methods:

• Methylation interference footprinting to identify critical DNA contact points.
• Mobility shift competition assays with synthetic oligonucleotides to define the core recognition sequence.
• Orthophenanthroline/Cu+ footprinting to probe metal ion involvement.

Main Results:

• Evidence suggests a divalent metal ion, likely Zn2+, is an essential cofactor for Ah receptor DNA binding.
• The consensus DNA recognition sequence for the Ah receptor was determined as CNA/TNA/TCACGCA/TA/T.
• Chelators inhibited DNA binding, an effect reversed by Zn2+, indicating a requirement for metal ions.

Conclusions:

• The aryl hydrocarbon (Ah) receptor requires a divalent metal ion, likely Zn2+, for sequence-specific DNA binding.
• This Zn2+ requirement is analogous to that of other nuclear receptors, supporting its classification within the steroid/thyroid hormone receptor superfamily.
• Metal ion binding is critical for receptor function and becomes inaccessible upon DNA binding.