Structures of neurokinin 1 receptor in complex with G and G proteins reveal substance P binding mode and unique activation features.

The neurokinin 1 receptor (NKR) is involved in inflammation and pain transmission. This pathophysiologically important G protein–coupled receptor is predominantly activated by its cognate agonist substance P (SP) but also by the closely related neurokinins A and B. Here, we report cryo–electron microscopy structures of SP-bound NKR in complex with its primary downstream signal mediators, G and G. Our structures reveal how a polar network at the extracellular, solvent-exposed receptor surface shapes the orthosteric pocket and that NKR adopts a noncanonical active-state conformation with an interface for G protein binding, which is distinct from previously reported structures. Detailed comparisons with antagonist-bound NKR crystal structures reveal that insurmountable antagonists induce a distinct and long-lasting receptor conformation that sterically blocks SP binding. Together, our structures provide important structural insights into ligand and G protein promiscuity, the lack of basal signaling, and agonist- and antagonist-induced conformations in the neurokinin receptor family.