Three-dimensional structure-function relationship of vitamin D and vitaminD receptor model

On the basis of conformational analysis of the vitamin D side chain and stu dies using conformationally restricted synthetic vitamin D analogs, we have suggested the active space region concept of vitamin D: The vitamin D side -chain region was grouped into four regions (A, G, EA and EG) and the A and EA regions were suggested to be important for vitamin D actions. We extend ed our theory to known highly potent vitamin D analogs and found a new regi on F. The analogs which occupy the F region have such modifications as 22-o xa, 22-ene, 16-ene and 18-nor. Altogether, the following relationship betwe en the space region and activity was found: Affinity for vitamin D receptor (VDR), EA > A > F > G > EG; Affinity for vitamin D binding protein (DBP), A >> G,EA,EG; Target gene transactivation, EA > F > A > EG greater than or equal to G; Cell differentiation, EA > F > A > EG greater than or equal to G; Bone calcium mobilization, EA > GA > F greater than or equal to EG; Inte stinal calcium absorption, EA = A greater than or equal to G >> EG. We mode led the 3D structure of VDR-LBD (ligand binding domain) using hRAR gamma as a template, to develop our structure-function theory into a theory involvi ng VDR. 1 alpha ,25(OH)(2)D-3 was docked into the ligand binding pocket of the VDR with the side chain heading the wide cavity at the H-11 site, the A -ring toward the narrow beta -turn site, and the beta -face of the CD ring facing H3. Amino acid residues forming hydrogen bonds with the 1 alpha- and 25-OH groups were specified: S237 and R274 forming a pincer type hydrogen- bond for the 1 alpha -OH and H397 for the 25-OH. Mutants of several amino a cid residues that are hydrogen-bond candidates were prepared and their biol ogic properties were evaluated. All of our mutation results together with k nown mutation data support our VDR model docked with the natural ligand. (C ) 2001 Elsevier Science Inc. All rights reserved.