Fig. 6.

Structural features and common activation mechanism of class B GPCRs. a, b Structural features of the peptide-binding pocket. The shift of peptide C-terminus (a) and ECD (b) is indicated as red arrows. The peptides urocortin 1 (UCN1)¹ bound to CRF1R (light blue, PDB code: 6PB0), UCN1² bound to CRF2R (salmon, PDB code: 6PB1), PACAP38 (red, PDB code: 6P9Y), long-acting PTH (LA-PTH, green, PDB code: 6NBF), GLP-1 (cyan, PDB code: 5VAI), sCT (yellow, PDB code: 6NIY), and CGRP (magenta, PDB code: 6PB1) are shown as cartoons. Binding poses of the antagonist (green) and allosteric ligand (salmon) are shown as sticks (c, PDB codes: 4K5Y, 5EE7, 4Z9G, 5VEW, and 5VEX). d, e The common activation mechanism of class B GPCRs as exampled by the structures of inactive GCGR (gray, PDB code 3NYA) and active VIP1R (green, PDB code 6VN7). Side chains of residues in three conserved polar network are shown in stick presentation. The conserved P^6.47bxxG^6.50b motifs in TM6 are shown as single red spheres