Structure, Energetics, and Dynamics of Binding Coactivator Peptide to the Human Retinoid X Receptor α Ligand Binding Domain Complex with 9-cis-Retinoic Acid

摘要

Retinoid X receptors (RXRs) are ligand-dependent nuclear receptors, which are activated by thenpotent agonist 9-cis-retinoic acid (9cRA). 9cRA binds to the ligand binding domain (LBD) of RXRs andnrecruits coactivator proteins for gene transcription. Using isothermal titration calorimetry, the binding of an13-mer coactivator peptide, GRIP-1, to the hRXRR-LBD homodimer complex containing 9cRA (hRXRR-nLBD:9cRA:GRIP-1) is reported between 20 and 37 u0002C. ΔG is temperature independent (-8.5 kcal/mol), andnGRIP-1 binding is driven by ΔH (-9.2 kcal/mol) at 25 u0002C. ΔCp is large and negative (-401 cal moln-1nK-1n).nThe crystal structure of hRXRR-LBD:9cRA:GRIP-1 is reported at 2.05 A ˚n.When the structures of hRXRR-nLBD:9cRA:GRIP-1 and hRXRR-LBD:9cRA (1FBY) homodimers are compared, E453 and E456 on helix 12nbury and form ionic interactions with GRIP-1. R302 on helix 4 realigns to form new salt bridges to both E453nand E456. F277 (helix 3), F437 (helix 11), and F450 (helix 12) move toward the hydrophobic interior. Thenchanges in the near-UV spectrum at 260 nm of the hRXRR-LBD:9cRA:GRIP-1 support this structuralnchange. Helix 11 tilts toward helix 12 by ≈1A ˚n, modifying the ring conformation of 9cRA. Hydrogen-ndeuterium exchangemass spectroscopy indicates GRIP-1 binding to hRXRR-LBD:9cRA significantly decreasesnthe exchange rates for peptides containing helices 3 (F277), 4 (R302), 11 (F437), and 12 (E453, E456). Thenstructural changes and loss of dynamics of the GRIP-1-bound structure are used to interpret the energetics ofncoactivator peptide binding to the agonist-bound hRXRR-LBD.