The basis for half-site specificity explored through a non-cognate steroid receptor-DNA complex

Area of Science:

• Molecular biology
• Structural biology
• Biochemistry

Background:

• Steroid receptors are crucial transcription factors that bind to specific DNA sequences called response elements.
• These response elements are bipartite, consisting of two six-base-pair half-sites.
• Two canonical half-site types exist, differing in their central two base pairs, dictating specific receptor binding.

Purpose of the Study:

• To investigate the structural basis of non-cognate DNA binding by steroid receptors.
• To elucidate the molecular interactions and defects when an estrogen receptor binds to a glucocorticoid response element.

Main Methods:

• X-ray crystallography was used to determine the structure of an estrogen receptor DNA-binding domain bound to a non-cognate DNA half-site.
• Structural analysis focused on the interface between the receptor and DNA, comparing it to cognate interactions.

Main Results:

• The crystal structure revealed that the estrogen receptor-like DNA-binding domain bound to a glucocorticoid response element (non-cognate) forms an interface resembling specific cognate interfaces.
• A key defect identified was altered helical geometry in the non-cognate DNA half-site, preventing a critical side-chain contact.
• This defect created a gap filled by multiple water molecules, potentially destabilizing the receptor-DNA interaction due to entropic penalties.

Conclusions:

• The study elucidates the structural mechanism underlying weakened binding of steroid receptors to non-cognate DNA half-sites.
• Altered DNA helical geometry and the role of water molecules are critical factors in the specificity and stability of steroid receptor-DNA interactions.
• Understanding these molecular details is vital for comprehending gene regulation by steroid receptors.