Ligand-specific structural changes in the vitamin D receptor in solution

Area of Science:

• Molecular Biology
• Structural Biology
• Endocrinology

Background:

• The vitamin D receptor (VDR) is a nuclear hormone receptor mediating diverse physiological actions.
• Understanding how different vitamin D analogues elicit specific VDR responses remains unclear.
• Previous crystallographic studies showed static VDR conformations despite varying ligand activities.

Purpose of the Study:

• To investigate ligand-induced conformational dynamics of the VDR ligand-binding domain (VDR-LBD) in solution.
• To elucidate the molecular mechanisms underlying differential VDR activation by various vitamin D analogues.

Main Methods:

• Utilized Nuclear Magnetic Resonance (NMR) spectroscopy to study rat VDR-LBD (rVDR-LBD) in solution.
• Analyzed differential chemical shifts upon binding of three distinct ligands: 1,25-dihydroxyvitamin D₃, 2MD (agonist), and OU-72 (antagonist).
• Mapped ligand-specific chemical shifts to identify affected protein residues.

Main Results:

• Observed ligand-specific chemical shifts in rVDR-LBD across multiple residues, both near and distant from the binding pocket.
• Agonist binding (1,25(OH)₂D₃ and 2MD) induced changes in helix-12, crucial for coactivator recruitment.
• Antagonist OU-72 binding led to the disappearance of signals from helices-11 and -12, indicating disorder and impaired coactivator attachment.

Conclusions:

• Solution dynamics of VDR-LBD, not just static crystal structures, are critical for differential ligand activity.
• Ligand-specific conformational changes, particularly in helix-12, dictate coactivator complex formation.
• Disruption of helix-11/12 structure by antagonists like OU-72 explains their inability to recruit coactivators.