- Xia G, Boerma LJ, Cox BD, Qiu C, Kang S, Smith CD, Renfrow MB, Muccio DD
- Structure, Energetics and Dynamics of Binding Coactivator Peptide to Human Retinoid X Receptor Alpha Ligand Binding Domain Complex with 9-cis-Retinoic Acid.
- Biochemistry. 2010 Nov 4.
- Retinoid X receptors (RXRs) are ligand-dependent nuclear receptors, which are activated by the potent agonist 9-cis retinoic acid (9cRA). 9cRA binds to the ligand binding domain (LBD) of RXRs, and recruits coactivator proteins for gene transcription. Using isothermal titration calorimetry, the binding of a 13-mer coactivator peptide, GRIP-1, to the hRXRalpha-LBD homodimer complex containing 9cRA (hRXRalpha-LBD:9cRA:GRIP-1) is reported between 20 degrees and 37 degrees C. DeltaG is temperature independent (-8.5 kcal/mol), and GRIP-1 binding is driven by DeltaH (-9.2 kcal/mol) at 25 degrees C. DeltaCp is large and negative (-401 cal/mol-K). The crystal structure of hRXRalpha-LBD:9cRA:GRIP-1 is reported at 2.05 A. When the structures of hRXRalpha-LBD:9cRA:GRIP-1 and hRXRalpha-LBD:9cRA (1FBY) homodimers are compared, E453 and E456 on helix 12 bury and form ionic interactions with GRIP-1. R302 on helix 4 realigns to form new salt bridges to both E453 and E456. F277 (helix 3), F437 (helix 11), and F450 (helix 12) move toward the hydrophobic interior. The changes in the near-UV spectrum at 260 nm of the hRXRalpha-LBD:9cRA:GRIP-1 support this structural change. Helix 11 tilts toward helix 12 by approximately 1 A modifying the ring conformation of 9cRA. Hydrogen-deuterium exchange mass spectroscopy indicate GRIP-1 binding to hRXRalpha-LBD:9cRA significantly decreases the exchange rates for peptides containing helices 3 (F277), 4 (R302), 11 (F437) and 12 (E453; E456). The structural changes and loss of dynamics of the GRIP-1 bound structure are used to interpret the energetics of coactivator peptide binding to the agonist-bound hRXRalpha-LBD.