Crystal Structures of Human Orexin 2 Receptor Bound to the Subtype-Selective Antagonist EMPA

Summary Orexinpeptides in the brain regulate physiological functions such as the sleep-wake cycle, and are thus drug targets for the treatment of insomnia. Using serial femtosecond crystallography and multi-crystal data collection with a synchrotron light source, we determined structures of human orexin2 receptor in complex with the subtype-selective antagonist EMPA( N -ethyl-2-[(6-methoxy-pyridin-3-yl)-(toluene-2- sulfonyl)-amino]- N -pyridin-3-ylmethyl- acetamide) at 2.30-A and 1.96-A resolution. In comparison with the non-subtype-selective antagonist suvorexant, EMPAcontacted fewer residues through hydrogen bonds at the orthosteric site, explaining the faster dissociation rate. Comparisons among these OX 2 R structures in complex with selective antagonistsand previously determined OX 1 R/OX 2 R structures bound to non-selective antagonistsrevealed that the residue at positions 2.61 and 3.33 were critical for the antagonistselectivity in OX 2 R. The importance of these residues for binding selectivityto OX 2 R was also revealed by molecular dynamics simulation. These results should facilitate the development of antagonistsfor orexin receptors.