Non-canonical G activation by orexin receptor type 2 and lemborexant observed in microsecond molecular dynamics simulations.

Orexins are hypothalamic neuropeptides primarily involved in regulating the sleep/wakefulness cycle and circadian rhythm. They bind to the orexin receptor type 1 (OX) and type 2 (OX), well-known drug targets in the treatment of sleep disorders, that have recently been shown to play a significant role in different cancers. Lemborexant is one of a few orexin receptor antagonists that have been approved for the treatment of insomnia. Despite being classified as an antagonist, lemborexant may display agonist-like behavior in the non-canonical signaling pathway of the orexin receptors, as confirmed recently in cancer cell models. Here, we generated a model of OX in complex with the full-length G protein and used it in the molecular dynamics (MD) study. We compared the impact of lemborexant and the OX-selective, potent agonist compound 1 on OX activation and subsequent guanosine diphosphate (GDP) to guanosine triphosphate (GTP) exchange in the Gα subunit. These 2 µs MD simulations showed that both ligands evoke similar, activation-like conformational changes in OX and explained the observed lemborexant-mediated apoptosis of cancer cells. In addition, MD simulations of the active-state OX-G complexes allowed us to uncover a sequence of micro- and macroscale events during the activation of G and to detect important micro- and macroswitches in the Gα subunit.