Selective G protein signaling driven by Substance P-Neurokinin Receptor structural 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 cryo-EM 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 deep in the NK1R pocket. 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.