title: Structural basis of the histidine-mediated vitamin D receptor agonistic and antagonistic mechanisms of (23S)-25-dehydro-1alpha-hydroxyvitamin D3-26,23-lactone.
abstract: TEI-9647 antagonizes vitamin D receptor (VDR) mediated genomic actions of 1alpha,25(OH)2D3 in human cells but is agonistic in rodent cells. The presence of Cys403, Cys410 or of both residues in the C-terminal region of human VDR (hVDR) results in antagonistic action of this compound. In the complexes of TEI-9647 with wild-type hVDR (hVDRwt) and H397F hVDR, TEI-9647 functions as an antagonist and forms a covalent adduct with hVDR according to MALDI-TOF MS. The crystal structures of complexes of TEI-9647 with rat VDR (rVDR), H305F hVDR and H305F/H397F hVDR showed that the agonistic activity of TEI-9647 is caused by a hydrogen-bond interaction with His397 or Phe397 located in helix 11. Both biological activity assays and the crystal structure of H305F hVDR complexed with TEI-9647 showed that the interaction between His305 and TEI-9647 is crucial for antagonist activity. This study indicates the following stepwise mechanism for TEI-9647 antagonism. Firstly, TEI-9647 forms hydrogen bonds to His305, which promote conformational changes in hVDR and draw Cys403 or Cys410 towards the ligand. This is followed by the formation of a 1,4-Michael addition adduct between the thiol (-SH) group of Cys403 or Cys410 and the exo-methylene group of TEI-9647.
authors.affiliation: Teijin Institute for Bio-Medical Research, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Kakuda
authors.forename: Seiichi
authors.initials: S
authors.lastname: Ishizuka
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Eguchi
authors.forename: Mathew T
authors.initials: MT
authors.lastname: Mizwicki
authors.forename: Anthony W
authors.initials: AW
authors.lastname: Norman
authors.forename: Midori
authors.initials: M
authors.lastname: Takimoto-Kamimura
mesh_terms: D002117:Calcitriol / Q000031:analogs & derivatives* / Q000737:chemistry; D018360:Crystallography, X-Ray; D006639:Histidine / Q000737:chemistry; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D018167:Receptors, Calcitriol / Q000819:agonists / Q000037:antagonists & inhibitors / Q000737:chemistry*
chemical_list: D008024:Ligands; D018167:Receptors, Calcitriol; C400545:TEI 9647; D006639:Histidine; D002117:Calcitriol