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The active metabolite of vitamin D3, 1α,25-dihydroxyvitamin D3, acts as a ligand for the vitamin D receptor ( VDR) and activates VDR-mediated gene expression. Recently, we characterized 1α,25-dihydroxyvitamin D3-26,23-lactams ( DLAMs), which mimic vitamin D3 metabolites, as noncalcemic VDR ligands that barely activate the receptor. In this study, we present structural insights onto the regulation of VDR function by DLAMs. X-ray crystallographic analysis revealed that DLAMs induced a large conformational change in the loop region between helices H6 and H7 in the VDR ligand-binding domain. Our structural analysis suggests that targeting of the loop region may be a new mode of VDR regulation. [ABSTRACT FROM AUTHOR]

Abstract: Non-secosteroidal ligands for vitamin D receptor (VDR) have been developed for the agonist with non-calcemic profiles. Here, we provide the structural mechanism of VDR agonism by novel non-secosteroidal ligands. All ligands had the similar efficacy, while two had the higher potency. Crystallographic analyses revealed that all ligands interacted with helix H10 and the loop between helices H6 and H7 in a similar manner, but also that the two ligands with higher potency had different interaction modes. This study suggests that distinct ligand potency depend upon differences in the formation and rearrangement of hydrogen-bond networks induced by each ligand. [Copyright &y& Elsevier]