Structural perspective of class B1 GPCR signaling

Class B1 G protein-coupled receptors (GPCRs) play important roles in human physiology and disease pathology. Using cryo-electron microscopy (cryo-EM) and X-ray crystallography, the 3D structures of all 15 members of this receptor subfamily have been determined in recent years at the near-atomic level. Although they share many structural commonalities, they show distinct features in terms of ligand recognition and receptor activation. In-depth structural analyses have yielded valuable insights into the N termini of both peptide hormones and cognate receptors, the outward movement of transmembrane helix 6 (TM6), the allosteric modulation sites located in the transmembrane domain (TMD), and the constitutive signaling bias mediated by receptor splice variants. These provide new directions for the design of better therapeutic agents, thereby making these targets more druggable.