The study explores the structural and molecular basis of interactions between nuclear receptors (NRs) and coactivators, focusing on the GRIP1 coactivator and the thyroid hormone receptor (TR). It reveals that hormone binding to the ligand-binding domain (LBD) of TR induces conformational changes that facilitate interactions with coactivators. Specifically, the LxxLL motif in GRIP1 interacts with a hydrophobic groove in the TR LBD, with the motif and adjacent residues determining the specificity of the interaction. The amphipathic α-helix of GRIP1 and the hydrophobic groove of the TR LBD form a stable interface, which is essential for coactivator binding and transcriptional activation. The study also shows that the interaction is influenced by the sequences adjacent to the LxxLL motif, with NR-box 2 being more preferred by TRβ than NR-box 3. Structural analysis of the TRβ LBD in complex with the NR-box 2 peptide revealed a hydrophobic groove formed by conserved residues in helices H3, H4, H5, and H12, which interacts with the amphipathic α-helix of GRIP1. The interaction is highly specific, with the hydrophobic residues and adjacent sequences playing critical roles. The study also highlights the importance of the LxxLL motif and its adjacent sequences in determining the specificity of interactions between NRs and coactivators. The findings suggest that the structural elements of the LBD and the coactivator interface contribute to the flexibility and specificity of combinatorial regulation in transcriptional control.The study explores the structural and molecular basis of interactions between nuclear receptors (NRs) and coactivators, focusing on the GRIP1 coactivator and the thyroid hormone receptor (TR). It reveals that hormone binding to the ligand-binding domain (LBD) of TR induces conformational changes that facilitate interactions with coactivators. Specifically, the LxxLL motif in GRIP1 interacts with a hydrophobic groove in the TR LBD, with the motif and adjacent residues determining the specificity of the interaction. The amphipathic α-helix of GRIP1 and the hydrophobic groove of the TR LBD form a stable interface, which is essential for coactivator binding and transcriptional activation. The study also shows that the interaction is influenced by the sequences adjacent to the LxxLL motif, with NR-box 2 being more preferred by TRβ than NR-box 3. Structural analysis of the TRβ LBD in complex with the NR-box 2 peptide revealed a hydrophobic groove formed by conserved residues in helices H3, H4, H5, and H12, which interacts with the amphipathic α-helix of GRIP1. The interaction is highly specific, with the hydrophobic residues and adjacent sequences playing critical roles. The study also highlights the importance of the LxxLL motif and its adjacent sequences in determining the specificity of interactions between NRs and coactivators. The findings suggest that the structural elements of the LBD and the coactivator interface contribute to the flexibility and specificity of combinatorial regulation in transcriptional control.