The solution structure of the human retinoic acid receptor-β DNA-binding domain

The three-dimensional structure of the DNA-binding domain of the human retinoic acid receptor-ß (hRAR-ß) has been determined by nuclear magnetic resonance spectroscopy in conjunction with distance geometry, restrained molecular dynamics and iterative relaxation matrix calculations. A total of 1244 distance restraints were obtained from NOE intensities, of which 448 were intra-residue and 796 inter-residue restraints. In addition 23 ? and 30 ? dihedral angle restraints were obtained from J-coupling data. The two ‘zinc-finger’ regions of the 80-amino acid residue protein are followed by two a-helices that cross each other perpendicularly. There is a short stretch of b-sheet near the N-terminus. The a-helical core of the protein is well determined with a backbone root-mean-square deviation (r.m.s.d.) with respect to the average of 0.18 Å and 0.37 Å when the side chains of residues 31, 32, 36, 61, 62, 65 and 69 are included. The r.m.s.d. for the backbone of residues 5–80 is 0.76 Å. For the first finger (residues 8–28), the r.m.s.d. of the backbone is 0.79 Å. For the second finger (residues 44–62) the r.m.s.d. is 0.64 Å. The overall structure is similar to that of the corresponding domain of the glucocorticoid receptor, although the C-terminal part of the protein is different. The second a-helix is two residues shorter and is followed by a well-defined region of extended backbone structure.