tokens: Therefore , in VDR - mediated transcriptional activation , 1 , 25 ( OH ) 2D3 binding to VDR alters the conformation of the ligand binding domain such that it : ( i ) engages in strong heterodimerization with RXR to facilitate VDRE binding , ( ii ) influences the RXR ligand binding domain such that it is resistant to the binding of 9 - cis RA but active in recruiting coactivator to its AF - 2 and ( iii ) presents the AF - 2 region in VDR for coactivator association .