Structural basis for the cell-specific activities of the NGFI-B and the Nurr1 ligand-binding domain.
NGFI-B is a ligand-independent orphan nuclear receptor of the NR4A subfamily that displays important functional differences with its homolog Nurr1. In particular, the NGFI-B ligand-binding domain (LBD) exhibits only modest activity in cell lines in which the Nurr1 LBD strongly activates transcription. To gain insight into the structural basis for the distinct activation potentials, we determined the crystal structure of the NGFI-B LBD at 2.4-angstroms resolution. Superimposition with the Nurr1 LBD revealed a significant shift of the position of helix 12, potentially caused by conservative amino acids exchanges in helix 3 or helix 12. Replacement of the helix 11-12 region of Nurr1 with that of NGFI-B dramatically reduces the transcriptional activity of the Nurr1 LBD. Similarly, mutation of Met414 in helix 3 to leucine or of Leu591 in helix 12 to isoleucine (the corresponding residues found in NGFI-B) significantly affects Nurr1 transactivation. In comparison, swapping the helix 11-12 region of Nurr1 into NGFI-B results in a modest increase of activity. These observations reveal a high sensitivity of LBD activity to changes that influence helix 12 positioning. Furthermore, mutation of hydrophobic surface residues in the helix 11-12 region (outside the canonical co-activator surface constituted by helices 3, 4, and 12) severely affects Nurr1 transactivation. Together, our data suggest that a novel co-regulator surface that includes helix 11 and a specifically positioned helix 12 determine the cell type-dependent activities of the NGFI-B and the Nurr1 LBD.
Flaig
Ralf
R
Département de Biologie et Génomique Structurales, IGBMC, CNRS/INSERM/ULP, 1 Rue Laurent Fries, B.P. 10142, Illkirch 67404, France.
Greschik
Holger
H
Peluso-Iltis
Carole
C
Moras
Dino
D
D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D018360:Crystallography, X-Ray; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000502:physiology*; D019281:Dimerization; D006639:Histidine / Q000737:chemistry; D007930:Leucine / Q000737:chemistry; D008024:Ligands; D008715:Methionine / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D057105:Nuclear Receptor Subfamily 4, Group A, Member 1; D057126:Nuclear Receptor Subfamily 4, Group A, Member 2; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000502:physiology*; D011987:Receptors, Steroid / Q000737:chemistry* / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry* / Q000502:physiology*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection
D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D008024:Ligands; C539820:Nr4a1 protein, rat; C539884:Nr4a2 protein, rat; D057105:Nuclear Receptor Subfamily 4, Group A, Member 1; D057126:Nuclear Receptor Subfamily 4, Group A, Member 2; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D014157:Transcription Factors; D006639:Histidine; D008715:Methionine; D007930:Leucine