Structural basis of CD97 activation and G-protein coupling.

CD97 (ADGRE5) is an adhesion G protein-coupled receptor (aGPCR) which plays crucial roles in immune system and cancer. However, the mechanism of CD97 activation and the determinant of G coupling selectivity remain unknown. Here, we present the cryo-electron microscopy structures of human CD97 in complex with G, G, and G. Our structures reveal the stalk peptide recognition mode of CD97, adding missing information of the current tethered-peptide activation model of aGPCRs. For instance, a revised "FXφφφ" motif and a framework of conserved aromatic residues in the ligand-binding pocket. Importantly, structural comparisons of G, G, and G engagements of CD97 reveal key determinants of G coupling selectivity, where a deep insertion of the α helix 5 and a closer contact with the transmembrane helix 6, 5, and 3 dictate coupling preferences. Taken together, our structural study of CD97 provides a framework for understanding CD97 signaling and the G coupling selectivity.