ABSTRACT
Retinoid-related orphan receptor gamma (RORγ) directly controls the differentiation of Th17 cell and the production of interleukin-17, which plays an integral role in autoimmune diseases. To obtain insight into RORγ, we have determined the first crystal structure of a ternary complex containing RORγ ligand-binding domain (LBD) bound with a novel synthetic inhibitor and a repressor peptide, 22-mer peptide from silencing mediator of retinoic acid and thyroid hormone receptor (SMRT). Comparison of a binary complex of nonliganded (apo) RORγ-LBD with a nuclear receptor co-activator (NCoA-1) peptide has shown that our inhibitor displays a unique mechanism different from those caused by natural inhibitor, ursolic acid (UA). The compound unprecedentedly induces indirect disruption of a hydrogen bond between His479 on helix 11 (H11) and Tyr502 on H12, which is crucial for active conformation. This crystallographic study will allow us to develop novel synthetic compounds for autoimmune disease therapy.
Subject(s)
Nuclear Receptor Co-Repressor 2/metabolism , Nuclear Receptor Coactivator 1/metabolism , Nuclear Receptor Subfamily 1, Group F, Member 3/metabolism , Binding Sites , Humans , Hydrogen Bonding , Models, Molecular , Mutation , Nuclear Receptor Co-Repressor 2/agonists , Nuclear Receptor Co-Repressor 2/chemistry , Nuclear Receptor Co-Repressor 2/genetics , Nuclear Receptor Coactivator 1/chemistry , Nuclear Receptor Coactivator 1/genetics , Peptide Fragments , Protein Binding , Protein Conformation , Triterpenes/pharmacology , Ursolic AcidABSTRACT
The absolute stereochemistry of (-)-galbonolide A (1) was assigned by chemical methods. First, 1 was degraded to diol 3. After selective silylation of the primary alcohol, two independent methods were carried out to determine the chirality at C13. Both established its S-configuration. Using the methodology developed in the total synthesis of (-)-galbonolide B, diols 13(S,S) and 13(S,R) were prepared. Their (R)-MTPA esters, 14(S,S,R) and 14(S,R,R), were compared with the analogous (R)-MTPA ester of the degradation product 3, which subsequently established the S-chirality at C8. To determine the chirality at C4, two independent methods were carried out. One involved a comparison with the chirality of C4 of galbonolide B. The other involved a comparison of the degradation product of galbonolide A, 22, with its synthetic equivalents. Both methods confirmed the S-configuration at C4. Since three of the four chiral centers of galbonolides A and B have been confirmed to be identical and since the two galbonolides share very similar conformations as suggested by their (1)H NMR spectra, the configurations at C2 of these two compounds should also be the same.
