Abstract
Vitamin D actions are expressed through binding to specific proteins related to metabolism, transport and transcription. The proteins are cytochrome P450 (CYP) which is vitamin D hydroxylase, vitamin D binding protein (DBP) which is a plasma carrier protein of vitamin D, and vitamin D receptor (VDR) which is gene transcription factor. Vitamin D directly binds to these proteins. In recent years, crystal structures of CYP, DBP and VDR were analyzed and binding modes of vitamin D to these proteins were also shown. In this review, I summarize the crystal structures of CYP2R1/vitamin D_3, CYP24A1/detergent, DBP/25-hydroxyvitmain D_3 and VDR/ligand complexes. Crystal structures showed that the hydroxyl group of vitamin D forms a specific hydrogen bond with the protein and the remaining part of vitamin D interacts with hydrophobic residues of the protein. Interestingly, vitamin D in the complexes adopted specific conformation to adapt to the binding site of each protein. The information obtained from the structural analyses of vitamin D and related proteins is strongly expected to open an interesting new perspective to develop alternative drugs for treatment of vitamin D-related diseases.
