Crystal structure of the human vitamin D receptor ligand binding domain complexed with (1R,2R,3R)-5-[(E)-2-{(1R,3aS,7aR)-1-[(R)-6-hydroxy-6-methylheptan-2-yl]-7a-methyl-2,3,3a,6,7,7a-hexahydro-1H-inden-4-yl}vinyl]-2-(3-hydroxypropyl)cyclohex-4-ene-1,3-diol