Dynamics of the PAC1 receptor in apo, peptide agonist-bound, and G protein complexed states

G protein-coupled receptors (GPCRs) are key regulators of intercellular communication. One sub-family, named class B1 GPCRs, including the pituitary adenylate cyclase-activating polypeptide 1 receptor (PAC1R), is important for metabolic, cardiovascular, and endocrine functions. Currently, there is a wealth of structural data describing the active G protein-coupled state of class B1 GPCRs, and more limited information on inactive or intermediate states. Although these structures provide insight into conformational differences between different activation states, the receptor dynamics underpinning them remain largely unknown. Here, we employed hydrogen deuterium exchange mass spectrometry (HDX-MS) to investigate the dynamics of PAC1R across three distinct states: inactive (apo), intermediate (peptide agonist-bound), and fully active (peptide agonist and G protein-bound). This revealed dynamics of different states along the PAC1R activation pathway and deepens the understanding of class B1 GPCR dynamics and molecular mechanisms of receptor activation.