Crystal Structures of the Vitamin D Nuclear Receptor Liganded with the Vitamin D Side Chain Analogues Calcipotriol and Seocalcitol, Receptor Agonists of Clinical Importance. Insights into a Structural Basis for the Switching of Calcipotriol to a Receptor Antagonist by Further Side Chain Modification

Abstract

The plethora of actions of 1alpha,25(OH)(2)D(3) in various systems suggested wide clinical applications of vitamin D nuclear receptor (VDR) ligands in treatments of inflammation, dermatological indication, osteoporosis, cancers, and autoimmune diseases. More than 3000 vitamin D analogues have been synthesized in order to reduce the calcemic side effects while maintaining the transactivation potency of these ligands. Here, we report the crystal structures of VDR ligand binding domain bound to two vitamin D agonists of therapeutical interest, calcipotriol and seocalcitol, which are characterized by their side chain modifications. These structures show the conservation of the VDR structure and the adaptation of the side chain anchored by hydroxyl moieties. The structure of VDR-calcipotriol helps us to understand the structural basis for for the switching of calcipotriol to a receptor antagonist by further side chain modification. The VDR-seocalcitol structure, in comparison with the structure of VDR-KH1060, a superagonist ligand closely related to seocalcitol, shows adaptation of the D ring and position of C-21 in order to adapt its more rigid side chain.

The vitamin D receptor interacts preferentially with DRIP205-like LxxLL motifs

“…Nuclear receptor-coactivator interactions are mediated by LxxLL motifs located in the coactivator protein that interact with the AF-2 region of a nuclear receptor [9,10]. In this study, we screened a (x) 7 LxxLL(x) 7 phage library against VDR in the presence of 1,25 (OH) 2 D 3 or ZK159222, a selective antagonist of VDR-mediated transcription that competes with the natural ligand for binding to VDR [22][23][24]. Our agonist-derived class of LxxLL peptides showed strong sequence conservation across the region N-terminal to the LxxLL box giving the consensus sequence Lx E/H x H/F P L/M/I LxxLL, which was also consistent with the first three residues N-terminal to the DRIP 205 LxxLL motif.…”

On the Mechanism Underlying (23S)-25-Dehydro-1α(OH)-vitamin D3-26,23-lactone Antagonism of hVDRwt Gene Activation and Its Switch to a Superagonist

“…Crucial to 1,25D-hVDR Transactivation-Based on the hVDR x-ray crystallographic results (5,(25)(26)(27) His-305 and His-397 form hydrogen bonds (H-bonds) with the 25-OH group of 1,25D (28,29) (Fig. 2).…”

New insights into Vitamin D sterol-VDR proteolysis, allostery, structure–function from the perspective of a conformational ensemble model

“…1C, yellow circles). Residues N424, E425, I426, and S427 are unresolved in the 1,25D-VDR x-ray structures [11,12,13,14,15], but when added in an α-helical orientation to the x-ray construct (pdb code: 1DB1), prior to assembly minimization, it was observed that R402 (H11) formed Coulombic interactions with either E425 and S398 or S427 and S398 (see methods; Fig. 1C, pink ribbon in yellow circle).…”

“…1B), have shown that agonists occupy the same relative steric space in the VDR LBD, termed the genomic pocket (G-pocket), and stabilize only the closed helix-12 conformation (VDR-c1, Fig. 1C) [11,12,13,14,15]. Analysis of these VDR structures and molecular models with complete AF2-domains, reveal that unlike any other hormonally regulated NR, H12 is held in the closed conformation (c1) by three salt-bridges: 1) K264---E420 2) R154---K413/ R154---L414/ R154---D232 and 3) R402---S427/ S398/ E425 (Fig.…”