Ligand recognition by the vitamin D receptor

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Pharmacology

Background:

• The vitamin D receptor (VDR) plays a crucial role in gene regulation.
• Understanding VDR's interaction with ligands is key to developing new therapeutics.
• Previous studies solved the VDR's structure with its natural ligand.

Purpose of the Study:

• To investigate the VDR's recognition and interaction mechanisms with novel synthetic ligands.
• To elucidate the structural basis for selective VDR activation by specific synthetic compounds.
• To develop computational models for VDR-ligand interactions.

Main Methods:

• Computational docking studies of VDR with three synthetic ligands: 22-oxa-1,25-(OH)(2)D(3) (OCT), 20-epi-1,25-(OH)(2)D(3), and 20-epi-22-oxa-24,26,27-trihomo-1,25-(OH)(2)D(3).
• Site-directed mutagenesis of VDR ligand-binding pocket residues.
• Transactivation assays to evaluate ligand-induced VDR activity in VDR mutants.

Main Results:

• Docking models were generated for VDR with synthetic ligands.
• Mutagenesis identified key residues (L233, R274, W286, H397, Y401) essential for binding all tested ligands.
• Residues S278 and Q400 showed no importance, while others exhibited variable importance based on ligand structure.
• Structural factors conferring selective action to OCT and enhanced activity to 20-epi-ligands were proposed.

Conclusions:

• Specific amino acid residues in the VDR ligand-binding pocket are critical for recognizing and interacting with diverse ligands.
• The study provides insights into the structural determinants of VDR's selective and augmented activities.
• Docking models align with the proposed active space-region theory of vitamin D action.