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Structural analysis of RXR-VDR interactions on DR3 DNA
Paul L Shaffer1, Daniel T Gewirth
1Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA.
Summary
Researchers engineered Vitamin D receptor (VDR) mutants to form heterodimers with retinoid X receptor (RXR). This structural insight into VDR-RXR complexes advances understanding of gene regulation by these crucial receptors.
Area of Science:
- Molecular Biology
- Structural Biology
- Endocrinology
Background:
- The Vitamin D receptor (VDR) is a transcription factor that regulates gene expression.
- VDR typically forms dimers (homo- or heterodimers) on DNA response elements.
- Ligand binding to full-length VDR promotes heterodimerization with the 9-cis retinoic acid receptor (RXR).
Purpose of the Study:
- To investigate the DNA-binding domain (DBD) interactions between VDR and RXR.
- To engineer VDR mutants capable of forming heterodimeric DBD complexes with RXR.
- To determine the structure of a VDR-RXR DBD heterodimer.
Main Methods:
- Engineering of VDR mutants to disrupt homodimerization.
- Co-expression and purification of VDR and RXR DBDs.
- Crystallization and X-ray diffraction analysis of a VDR-RXR DBD heterodimer complex.
Main Results:
- VDR and RXR DBDs alone preferentially form homodimers.
- Engineered VDR mutants facilitate heterodimer formation with RXR DBD on DR3 elements.
- The crystal structure of a VDR-RXR DBD heterodimer was determined, revealing a non-physiological orientation due to crystal packing.
Conclusions:
- VDR DBD homodimerization is favored in the absence of the full VDR ligand-binding domain.
- Engineered VDR mutants can overcome this preference to form functional heterodimers with RXR DBD.
- The determined structure suggests that elements outside the core DBD are critical for heterodimer specificity and DNA recognition.