Two distinct dimerization interfaces differentially modulate target gene specificity of nuclear hormone receptors

Area of Science:

• Molecular Biology
• Endocrinology
• Structural Biology

Background:

• Nuclear receptors, such as the all-trans retinoic acid receptor (RAR) and 9-cis retinoic acid receptor (RXR), form heterodimers.
• These heterodimers exhibit flexible DNA binding, recognizing various DNA repeat sequences.
• Previous studies identified DNA-binding domain (DBD) interfaces crucial for specific DNA repeat recognition.

Purpose of the Study:

• To identify and characterize an additional dimerization domain within the ligand-binding domains (LBDs) of nuclear receptors.
• To elucidate the sequential mechanism of nuclear receptor heterodimerization and its impact on DNA binding specificity.

Main Methods:

• Localization of a transferable 40-amino acid region within the LBDs of RXR, RAR, thyroid hormone receptor (TR), and chicken ovalbumin upstream promoter transcription factor.
• Analysis of the role of this LBD region in heterodimeric interactions and DNA binding affinity.
• Integration of structural data from RXR LBD crystal structures.

Main Results:

• A conserved 40-amino acid region in the LBDs is critical for heterodimer identity and high-affinity DNA binding.
• This LBD dimerization interface initiates the formation of solution heterodimers with broad DNA recognition capabilities.
• Subsequent formation of a DBD dimerization interface restricts DNA binding to specific direct repeat elements.

Conclusions:

• Nuclear receptor dimerization occurs sequentially, initiated by the LBD interface and refined by the DBD interface.
• This dual-interface mechanism provides dynamic DNA-binding potential, increasing hormonal response diversity while ensuring physiological specificity.
• The LBD dimerization domain is essential for initial heterodimer formation, while the DBD dimerization domain confers target sequence restriction.