Transient GPCR states reveal how NTSR1 chooses its G proteins

Time-resolved cryo-EM maps reveal multiple GTP-bound intermediate states for the NTSR1–Gi1 and NTSR1–G11 complexes, showing that receptor intracellular loops ICL2 and ICL3, along with G protein regions, shape subtype selectivity beyond nucleotide-free structures. Gi1 forms more stable intermediates and dissociates slower than G11, explaining differential signaling, and swapping ICL2/ICL3 between NTSR1 and MOR disrupts these intermediates and signaling, highlighting a dynamic, intermediate-state mechanism underlying GPCR–G protein coupling and selectivity.