Identification of a novel co-regulator interaction surface on the ligand binding domain of Nurr1 using NMR footprinting

The nuclear receptor Nurr1 is a transcription factor essential for the development of midbrain dopaminergic neurons in vertebrates. Recent crystal structures of the Nurr1 ligand binding domain (LBD) and the Drosophila orthologue dHR38 revealed that, although these receptors share the classical LBD architecture, they lack a ligand binding cavity. This volume is instead filled with bulky hydrophobic side chains. Furthermore the canonical non-polar co-regulator binding groove is filled with polar side chains; thus, the regulation of transcription by this sub-family of nuclear receptor LBDs may be mediated by some other interaction surface on the LBD. We report here the identification of a novel co-regulator interface on the LBD of Nurr1. We used an NMR footprinting strategy that facilitates the identification of an interaction surface without the need of a full assignment. We found that non-polar peptides derived from the co-repressors SMRT and NCoR bind to a hydrophobic patch on the LBD of Nurr1. This binding surface involves a groove between helices 11 and 12. Mutations in this site abolish activation by the Nurr1 LBD. These findings give insight into the unique mechanism of action of this class of nuclear receptors.