Structure of the glucagon receptor in complex with a glucagon analogue

Abstract

Class B G-protein-coupled receptors (GPCRs), which consist of an extracellular domain (ECD) and a transmembrane domain (TMD), respond to secretin peptides to play a key part in hormonal homeostasis, and are important therapeutic targets for a variety of diseases. Previous work has suggested that peptide ligands bind to class B GPCRs according to a two-domain binding model, in which the C-terminal region of the peptide targets the ECD and the N-terminal region of the peptide binds to the TMD binding pocket. Recently, three structures of class B GPCRs in complex with peptide ligands have been solved. These structures provide essential insights into peptide ligand recognition by class B GPCRs. However, owing to resolution limitations, the specific molecular interactions for peptide binding to class B GPCRs remain ambiguous. Moreover, these previously solved structures have different ECD conformations relative to the TMD, which introduces questions regarding inter-domain conformational flexibility and the changes required for receptor activation. Here we report the 3.0 Å-resolution crystal structure of the full-length human glucagon receptor (GCGR) in complex with a glucagon analogue and partial agonist, NNC1702. This structure provides molecular details of the interactions between GCGR and the peptide ligand. It reveals a marked change in the relative orientation between the ECD and TMD of GCGR compared to the previously solved structure of the inactive GCGR-NNC0640-mAb1 complex. Notably, the stalk region and the first extracellular loop undergo major conformational changes in secondary structure during peptide binding, forming key interactions with the peptide. We further propose a dual-binding-site trigger model for GCGR activation-which requires conformational changes of the stalk, first extracellular loop and TMD-that extends our understanding of the previously established two-domain peptide-binding model of class B GPCRs.

PAC1 Receptors: Shapeshifters in Motion

“…1B). This singular distinguishing feature appears key in maintaining the open state of the PAC1 receptor for hundreds of microseconds; indeed, MD simulation of the receptor with the 21-amino acid segment deletion resulted in rapid open to closed state transition within 0.1 μsec, comparable to the transition times observed previously for the glucagon receptor (Yang et al 2015; Zhang et al 2018). …”

“…This structural detail allowed stabilization of the GCGR ECD in an inactive open state. However, more recent structural solutions of the full-length GCGR with the modified glucagon partial agonist NNC1702 revealed that upon peptide binding to the ECD, the linker/stalk region was poised as an α-helix similar to the original solution (PBDID: 4L6R); further, the ECL1 no longer interacted with linker but formed a short α-helix that may help to stabilize peptide–receptor interactions (Zhang et al 2018). Hence, glucagon peptide binding to the GCGR in this open conformation has been hypothesized to displace the ECL1–linker interaction to facilitate peptide-bound GCGR dynamics for TMD activation.…”

“…Perhaps not surprisingly, nearly 40% of all pharmaceutical drugs target class A receptors (Luttrell et al 2015; Zhang et al 2015). The structural solutions to the class B receptors, which encompass 15 members including CRH, glucagon, GLP-1, secretin, vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP) receptors, have lagged and the 7TM structures of only 4 members have become available only within the last 5 years (Hollenstein et al 2013; Siu et al 2013; Yang et al 2015; Jazayeri et al 2016; Jazayeri et al 2017; Liang et al 2017; Song et al 2017; Zhang et al 2017a; Zhang et al 2018). Although class B receptors are fewer in number, these receptors are increasingly being recognized as mediating some of the most critical physiological functions, including feeding and energy balance, sensory mechanisms, bone metabolism and stress responses (Harmar et al 2012; Culhane et al 2015).…”

An Inverse Agonist Ligand of the PTH Receptor Partially Rescues Skeletal Defects in a Mouse Model of Jansen's Metaphyseal Chondrodysplasia

“…PTHR1 is a family B G-protein-coupled receptor (GPCR) and, as for each of these receptors, binds its agonist peptide ligands, such as the bioactive PTH(1-34) fragment, via a two-site mechanism. This mechanism involves an initial docking of the (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34) portion of the ligand to the amino-terminal extracellular domain (ECD) portion of the receptor and a subsequent engagement of the N-terminal (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) portion of the ligand with the extracellular loop and seven-transmembrane helical domain (TMD) region of the receptor, which leads to receptor activation. (10,11) The recent high-resolution X-ray crystal (12) and cryogenic electron microscopy (cryo-EM) (13) structures of the PTHR1, each in complex with a PTH or PTHrP analog ligand, confirm and extend this model of ligand binding.…”

Assessment of Conformational State Transitions of Class B GPCRs Using Molecular Dynamics

“…Accordingly, these receptors are pharmacological targets for a variety of disorders including osteoporosis, hypercalcemia, type 2 diabetes, obesity, migraine and related chronic pain disorders, anxiety and depression. Despite the great pharmacological interests, only two full-length Class B receptor structures [6–8] have been determined. The three-dimensional molecular structures remain entirely or partially elusive among most Class B members.…”