Ligand-Specific Structural Changes in the Vitamin D Receptor in Solution

Kiran K. Singarapu, Jinge Zhu, Marco Tonelli, Hongyu Rao, Fariba M. Assadi-Porter, William M. Westler, Hector F. DeLuca, John L. Markley
2011 Biochemistry  
Vitamin D receptor (VDR) is a member of the nuclear hormone receptor superfamily. When bound to a variety of vitamin D analogs, VDR manifests a wide diversity of physiological actions. The molecular mechanism by which different vitamin D analogs cause specific responses is not understood. The published crystallographic structures of the ligand binding domain of VDR (VDR-LBD) complexed with ligands that have differential biological activities have exhibited identical protein conformations. Here
more » ... e report that rat VDR-LBD (rVDR-LBD) in solution exhibits differential chemical shifts when bound to three ligands that cause diverse responses: the natural hormone, 1,25-dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ], a potent agonist analog, 2methylene-19-nor-(20S)-1,25-dihydroxyvitamin D 3 [2MD], and an antagonist, 2-methylene-(22E)-(24R)-25-carbobutoxy-26,27-cyclo-22-dehydro-1α,24-dihydroxy-19-norvitamin D 3 [OU-72]. Ligand-specific chemical shifts mapped not only to residues at or near the binding pocket but also to residues remote from the ligand binding site. The complexes of rVDR-LBD with native hormone and the potent agonist 2MD exhibited chemical shift differences in signals from helix-12, which is part of the AF2 transactivation domain that appears to play a role in the selective recruitment of co-activators. By contrast, formation of the complex of rVDR-LBD with the antagonist OU-72 led to disappearance of signals from residues in helices-11 and 12. We present evidence that disorder in this region of the receptor in the antagonist complex prevents the attachment of co-activators. VDR belongs to the type II class of nuclear hormone receptor superfamily, which comprises proteins that share a common structural architecture and are localized in the cell nucleus. 1 1α,25-Dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ], the natural hormone that interacts with VDR, has been investigated in clinical treatment of divergent diseases including osteoporosis, cancers, autoimmune dysfunctions, cardiovascular diseases and infections. 2-4 A recent study of the human genome sequence suggested that VDR binds to more than 2700 sites on the DNA and affects the expression levels of at least 229 gene products in response to vitamin D3. 5 Many analogs of 1,25(OH) 2 D 3 have been prepared in an attempt to target specific actions of vitamin D. 6 VDR exhibits a wide diversity of physiological activities when bound to different vitamin D analogs; however, the molecular mechanism behind the ability of different vitamin D analogs to cause this diversity is yet to be elucidated. † Dedicated to the memory of Norma Marchesini
doi:10.1021/bi201637p pmid:22112050 pmcid:PMC3246842 fatcat:bolrmjrw6vfcjel5dhsee6ooku