Crystal structure of the human OX2 orexin receptor bound to the insomnia drug suvorexant

Abstract

The orexin (also known as hypocretin) G protein-coupled receptors (GPCRs) respond to orexin neuropeptides in the central nervous system to regulate sleep and other behavioural functions in humans. Defects in orexin signalling are responsible for the human diseases of narcolepsy and cataplexy; inhibition of orexin receptors is an effective therapy for insomnia. The human OX2 receptor (OX2R) belongs to the β branch of the rhodopsin family of GPCRs, and can bind to diverse compounds including the native agonist peptides orexin-A and orexin-B and the potent therapeutic inhibitor suvorexant. Here, using lipid-mediated crystallization and protein engineering with a novel fusion chimaera, we solved the structure of the human OX2R bound to suvorexant at 2.5 Å resolution. The structure reveals how suvorexant adopts a π-stacked horseshoe-like conformation and binds to the receptor deep in the orthosteric pocket, stabilizing a network of extracellular salt bridges and blocking transmembrane helix motions necessary for activation. Computational docking suggests how other classes of synthetic antagonists may interact with the receptor at a similar position in an analogous π-stacked fashion. Elucidation of the molecular architecture of the human OX2R expands our understanding of peptidergic GPCR ligand recognition and will aid further efforts to modulate orexin signalling for therapeutic ends.

Application of GPCR Structures for Modelling of Free Fatty Acid Receptors

“…Recent advances in structural biology of GPCRs have provided alternative templates for homology modelling of GPR120. Among currently available templates the orexin receptors (OX1 and OX2) have recently published crystal structures (Yin et al 2015;Yin et al 2016) and the highest sequence conservation, 30 % in the transmembrane region. Moreover, EL2 of the OX2 receptor has a similar length and some similarity (16 %), especially in the region after the disulfide bridge, making OX crystal structures more suitable templates than other available GPCR crystal structures.…”

From G Protein-coupled Receptor Structure Resolution to Rational Drug Design

“…The nucleotide antagonist MRS2500 binds to a site at the top of the transmembrane domain between TM6 and TM7 but also involving the N terminus and extracellular loop 2. This site is distinct from the nucleotide binding site found in P2Y 12 , which sits deeper in the receptor. Interestingly, previous mutation studies on P2Y 1 have indicated that some antagonists may bind deeper in the receptor at a site analogous to the P2Y 12 receptor (Ref.…”

“…The x-ray structures of the protease-activated PAR 1 receptor and the related class A purinergic receptor P2Y 12 both indicated the presence of multiple binding pockets within the transmembrane domain (37,38). In P2Y 12 , pocket 1 is formed between TM3 and TM7, whereas pocket 2 is formed between TM1-3 and TM7 (Fig. 1).…”

“…This is similar to the position of vorapaxar binding to the PAR1 receptor. Modeling and mutagenesis studies suggest that some P2Y 12 antagonists including those that bind covalently to the receptor may bind to pocket 2 rather than pocket 1 (38).…”

“…Structures of P2Y 12 have also been solved in complex with the full agonist 2MeSADP and the related 2MeSATP (39). These agonists bind to the same overall pocket as AZD1283 (i.e.…”