The importance of the putative helices 4 and 5 of human vitamin D-3 receptor for conformation and ligand binding

The 3-D structure of the human vitamin D-3 receptor has not been solved to date. To study the conformation of the ligand binding pocket and the amino acid residues important for binding of calcitriol and its synthetic 20-epi analog MC1288, we have introduced several point mutations into putative hel ices 4 and 5 of human vitamin D-3 receptor by site-directed mutagenesis, Th e amino acid residues Ser256, Glu257, Asp258, Gln259, Lys264, Ser265, Ser26 6, Glu269, Arg274, Ser278, and Phe279 were substituted by alanine. Our resu lts suggest that Arg274 is important for the binding of calcitriol and prob ably also for the binding of the synthetic vitamin D analog MC1288, whereas Asp258, Gln259, Glu269, and Phe279 may have an important role in stabilizi ng the conformation of hVDR after ligand binding. (C) 1999 Academic Press.