Specific structural motifs determine TRAP220 interactions with nuclear hormone receptors

Area of Science:

• Molecular Biology
• Gene Regulation
• Protein-Protein Interactions

Background:

• The TRAP coactivator complex enhances nuclear hormone receptor (NR) transcription.
• TRAP220, a subunit of TRAP, contains two LXXLL motifs for NR interaction.
• These motifs are crucial for coactivator binding to liganded receptors.

Purpose of the Study:

• To investigate the differential binding preferences of TRAP220's LXXLL motifs to various NRs.
• To elucidate the structural basis for these binding preferences.
• To determine the functional significance of both receptor binding domains (RBD-1 and RBD-2) in TRAP220 coactivation.

Main Methods:

• Site-directed mutagenesis to analyze LXXLL motif function.
• Assays to measure NR-coactivator interactions.
• Studies on TRAP220 binding to NR heterodimers.

Main Results:

• Specific NRs exhibit distinct preferences for RBD-1 or RBD-2 within TRAP220.
• Retinoid X receptor (RXR) prefers RBD-1, while thyroid hormone receptor (TR), vitamin D3 receptor (VDR), and PPAR favor RBD-2.
• Basic-polar residues at the N-terminus of the LXXLL motif dictate RBD-2 preference.
• Both RBD-1 and RBD-2 are essential for optimal TRAP220 association with RXR-TR or RXR-VDR heterodimers and coactivator activity.

Conclusions:

• TRAP220's two receptor binding domains display differential NR specificity.
• The structural features of the LXXLL motifs influence NR binding.
• TRAP220 can potentially interact with both subunits of a DNA-bound NR heterodimer, facilitating synergistic coactivation.