Structural basis for ligand-independent activation of the orphan nuclear receptor LRH-1.
The orphan nuclear receptors SF-1 and LRH-1 are constitutively active, but it remains uncertain whether their activation is hormone dependent. We report the crystal structure of the LRH-1 ligand binding domain to 2.4 A resolution and find the receptor to be a monomer that adopts an active conformation with a large but empty hydrophobic pocket. Adding bulky side chains into this pocket resulted in full or greater activity suggesting that, while LRH-1 could accommodate potential ligands, these are dispensable for basal activity. Constitutive LRH-1 activity appears to be conferred by a distinct structural element consisting of an extended helix 2 that provides an additional layer to the canonical LBD fold. Mutating the conserved arginine in helix 2 reduced LRH-1 receptor activity and coregulator recruitment, consistent with the partial loss-of-function phenotype exhibited by an analogous SF-1 human mutant. These findings illustrate an alternative structural strategy for nuclear receptor stabilization in the absence of ligand binding.
Sablin
Elena P
EP
Department of Biochemistry and Biophysics, University of California-San Francisco, San Francisco, CA 94143, USA.
Krylova
Irina N
IN
Fletterick
Robert J
RJ
Ingraham
Holly A
HA
D000595:Amino Acid Sequence; D001665:Binding Sites; D006528:Carcinoma, Hepatocellular / Q000473:pathology; D018360:Crystallography, X-Ray; D019281:Dimerization; D017930:Genes, Reporter; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010641:Phenotype; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured
D008024:Ligands; C431936:Nr5a2 protein, mouse; D018160:Receptors, Cytoplasmic and Nuclear