Cryo-EM structure of the human PAC1 receptor coupled to an engineered heterotrimeric G protein

Nat Struct Mol Biol. 2020 Mar;27(3):274-280. doi: 10.1038/s41594-020-0386-8. Epub 2020 Mar 9.


Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic neuropeptide hormone. The PACAP receptor PAC1R, which belongs to the class B G-protein-coupled receptors (GPCRs), is a drug target for mental disorders and dry eye syndrome. Here, we present a cryo-EM structure of human PAC1R bound to PACAP and an engineered Gs heterotrimer. The structure revealed that transmembrane helix TM1 plays an essential role in PACAP recognition. The extracellular domain (ECD) of PAC1R tilts by ~40° compared with that of the glucagon-like peptide-1 receptor (GLP-1R) and thus does not cover the peptide ligand. A functional analysis demonstrated that the PAC1R ECD functions as an affinity trap and is not required for receptor activation, whereas the GLP-1R ECD plays an indispensable role in receptor activation, illuminating the functional diversity of the ECDs in class B GPCRs. Our structural information will facilitate the design and improvement of better PAC1R agonists for clinical applications.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Baculoviridae / genetics
  • Baculoviridae / metabolism
  • Binding Sites
  • Cloning, Molecular
  • Cryoelectron Microscopy
  • Crystallography, X-Ray
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Gene Expression
  • Genetic Vectors / chemistry
  • Genetic Vectors / metabolism
  • Glucagon-Like Peptide-1 Receptor / chemistry*
  • Glucagon-Like Peptide-1 Receptor / genetics
  • Glucagon-Like Peptide-1 Receptor / metabolism
  • Humans
  • Models, Molecular
  • Peptides / chemistry*
  • Peptides / metabolism
  • Pituitary Adenylate Cyclase-Activating Polypeptide / chemistry*
  • Pituitary Adenylate Cyclase-Activating Polypeptide / genetics
  • Pituitary Adenylate Cyclase-Activating Polypeptide / metabolism
  • Protein Binding
  • Protein Conformation, alpha-Helical
  • Protein Conformation, beta-Strand
  • Protein Engineering
  • Protein Interaction Domains and Motifs
  • Protein Multimerization
  • Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I / chemistry*
  • Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I / genetics
  • Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I / metabolism
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Sf9 Cells
  • Spodoptera
  • Structural Homology, Protein


  • ADCYAP1 protein, human
  • GLP1R protein, human
  • Glucagon-Like Peptide-1 Receptor
  • Peptides
  • Pituitary Adenylate Cyclase-Activating Polypeptide
  • Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I
  • Recombinant Proteins