[NMR paper] Solution NMR Studies of the Ligand-Binding Domain of an Orphan Nuclear Receptor Reveals a Dynamic Helix in the Ligand-Binding Pocket.

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Solution NMR Studies of the Ligand-Binding Domain of an Orphan Nuclear Receptor Reveals a Dynamic Helix in the Ligand-Binding Pocket.

Solution NMR Studies of the Ligand-Binding Domain of an Orphan Nuclear Receptor Reveals a Dynamic Helix in the Ligand-Binding Pocket.

Biochemistry. 2018 Mar 16;:

Authors: Daffern N, Chen Z, Zhang Y, Pick L, Radhakrishnan I

Abstract
The ligand-binding domains (LBD) of the NR5A subfamily of nuclear receptors activate transcription via ligand-dependent and ligand-independent mechanisms. The Drosophila Ftz-F1 receptor (NR5A3) belongs to the latter category and its ligand-independence is attributed to a short helical segment (?6) within the protein that resides in the canonical ligand-binding pocket (LBP) in the crystalline state. Here, we show that the ?6 helix is dynamic in solution when Ftz-F1 is bound to the LxxLL motif of its cofactor Ftz, undergoing motions on the fast (picosecond-nanosecond) as well as slow (microsecond-millisecond) timescales. Motions on the slow timescale (ca. 10-3 s) appear to pervade through the domain, most prominently in the LBP and residues at or near the cofactor binding site. We ascribe the fast timescale motions to a solvent-accessible conformation for the ?6 helix akin to those described for its orthologs in higher organisms. We assign this conformation where the LBP is 'open' to a lowly-populated species while the major conformer bears the properties of the crystal structure where the LBP is 'closed'. We propose that these conformational transitions signal binding to small molecule ligands and/or play a role in cofactor dissociation from the binding site. Indeed, we show that Ftz-F1 LBD can bind phospholipids, not unlike its orthologs. Our studies provide the first detailed insights into intrinsic motions occurring on a variety of timescales in a nuclear receptor LBD and reveal that potentially functionally significant motions could pervade the domain in solution, despite evidence to the contrary implied by the crystal structure.


PMID: 29547262 [PubMed - as supplied by publisher]



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