Structure-function analysis of vitamin D and VDR model

Area of Science:

• Structural biology
• Molecular pharmacology
• Biochemistry

Background:

• Nuclear receptors (NR) possess a ligand-binding domain (LBD) with crucial roles in gene regulation.
• The three-dimensional structures of NR-LBDs reveal distinct conformations influencing transactivation.
• Vitamin D's biological functions are mediated through its interaction with the vitamin D receptor (VDR).

Purpose of the Study:

• To analyze the structure-function relationship of vitamin D by defining its active spatial regions.
• To investigate the binding interactions of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) with the VDR ligand-binding domain.
• To explore the structure-activity relationships of potent vitamin D analogs.

Main Methods:

• Systematic conformational analysis of vitamin D side chain.
• Conformationally restricted synthetic vitamin D analog studies.
• Homology modeling of VDR-LBD and molecular docking.
• Site-directed mutagenesis for VDR model validation.

Main Results:

• The vitamin D side chain was functionally grouped into five regions (A, G, EA, EG, F).
• Specific regions demonstrated differential activity for VDR binding, DBP binding, gene transactivation, cell differentiation, bone calcium mobilization, and intestinal calcium absorption.
• Key amino acid residues (R274, S237, H397) forming hydrogen bonds with 1,25-(OH)2D3 in the VDR-LBD were identified.
• A validated VDR-LBD/1,25-(OH)2D3 docking model was established.

Conclusions:

• The "active space region" concept provides a framework for understanding vitamin D's diverse biological activities.
• Precise interactions within the VDR-LBD are critical for vitamin D's signaling.
• The developed VDR model facilitates the study of novel vitamin D analogs with enhanced potency.