Selective G protein signaling driven by substance P–neurokinin receptor dynamics

The neuropeptide substance P (SP) is important in pain and inflammation. SP activates the neurokinin-1 receptor (NK1R) to signal via G q and G s proteins. Neurokinin A also activates NK1R, but leads to selective G q signaling. How two stimuli yield distinct G protein signaling at the same G protein-coupled receptor remains unclear. We determined cryogenic-electron microscopy structures of active NK1R bound to SP or the G q -biased peptide SP6–11. Peptide interactions deep within NK1R are critical for receptor activation. Conversely, interactions between SP and NK1R extracellular loops are required for potent G s signaling but not G q signaling. Molecular dynamics simulations showed that these superficial contacts restrict SP flexibility. SP6–11, which lacks these interactions, is dynamic while bound to NK1R. Structural dynamics of NK1R agonists therefore depend on interactions with the receptor extracellular loops and regulate G protein signaling selectivity. Similar interactions between other neuropeptides and their cognate receptors may tune intracellular signaling.