Structural basis of G _s and G _i recognition by the human glucagon receptor

Abstract

Class B G protein–coupled receptors, an important class of therapeutic targets, signal mainly through the Gs class of heterotrimeric G proteins, although they do display some promiscuity in G protein binding. Using cryo–electron microscopy, we determined the structures of the human glucagon receptor (GCGR) bound to glucagon and distinct classes of heterotrimeric G proteins, Gs or Gi1. These two structures adopt a similar open binding cavity to accommodate Gs and Gi1. The Gs binding selectivity of GCGR is explained by a larger interaction interface, but there are specific interactions that affect Gi more than Gs binding. Conformational differences in the receptor intracellular loops were found to be key selectivity determinants. These distinctions in transducer engagement were supported by mutagenesis and functional studies.

Differential GLP-1R binding and activation by peptide and non-peptide agonists

“…While the resolution of the published TT-OAD2 bound structure did not allow for the visualisation of waters , the almost identical rotameric positioning of these side chains suggest the same stabilisation networks exist. At the intracellular face of the receptor, all agonist-bound structures adopt an equivalent conformation with the most predominant feature being a large outward movement of TM6 relative to the inactive receptor, consistent with previous observations in active state structures of class B1 GPCRs ( Figure 5) (Liang et al, 2020a;Liang et al, 2020b;Liang et al, 2018a;Liang et al, 2018b;Liang et al, 2017;Ma et al, 2020;Qiao et al, 2020;Zhang et al, 2017;Zhao et al, 2019;. As all the structures are coupled to G protein, it is likely that the common interaction networks in the centre and base of the receptor, regardless of the agonist, are allosterically influenced by the presence of the bound G protein.…”

“…These receptors predominantly couple to the stimulatory protein Gs to promote cAMP production, however they can activate a range of signalling pathways and are highly susceptible to biased agonism (Wootten et al, 2017). In the past three years numerous active state structures of class B1 GPCRs coupled to the stimulatory protein Gs have been determined using single particle cryo-electron microscopy (cryo-EM) (Liang et al, 2020a;Liang et al, 2020b;Liang et al, 2018a;Liang et al, 2018b;Liang et al, 2017;Ma et al, 2020;Qiao et al, 2020;Zhang et al, 2017;Zhao et al, 2019). The resulting structures revealed common peptide binding pockets and a conserved Gs binding site within the receptor transmembrane (TM) helix bundle.…”

Capturing Peptide–GPCR Interactions and Their Dynamics

“…Based on the analysis of available structures, ligands of the secretin family keep their helical conformation in the receptor-bound state. Only the very N-terminal segment, which interacts with the transmembrane (TM) bundle is usually unwound [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. The situation for ligands of rhodopsin-like ligands is diverse: Some peptides are bound with their N-termini towards the TM bundle, others with their C-termini.…”

“…These include, in the rhodopsin branch, neurotensin at the NTS 1 R [ 7 , 8 , 9 , 10 ], endothelin 1 and 3 at the ET B receptor [ 11 , 12 ], angiotensin at the AT 1 R [ 13 , 14 ], as well as synthetic endorphin-derivatives at the μ and δ-opioid receptors [ 15 , 16 ], and an apelin-mimetic at the APJR [ 17 ]. In the secretin family, a number of G protein bound peptide–receptor complexes have been resolved via cryo-EM, which includes glucagon- and glucagon-like peptide 1 (GLP-1) analogues at the glucagon receptor [ 18 , 19 ] and GLP 1 R [ 20 , 21 , 22 ], respectively; urocortin (Ucn) and corticopin-releasing factor (CRF) at CRF 1 R and CRF 2 R [ 23 , 24 ], pituitary adenylate cyclase-activating peptide (PACAP) at PAC 1 R [ 24 ], parathyroid hormone at the PTH 1 R [ 25 ], and calcitonin-derivatives at the CGRP receptor [ 26 , 27 , 28 ].…”

“…How GPCRs select specific transducers remains enigmatic and cannot be firmly predicted from sequence or structural data alone [ 38 , 39 , 40 ]. Instead, the dynamic of the interactions and the existence several intermediate states may drive recognition and activation of the effector [ 19 , 41 , 42 ]. Thus, in order to understand the specific activation and signal transduction of GPCRs, it is essential to define the receptor–ligand interface ( Figure 1 A), the conformational changes of the ligand during binding ( Figure 1 B), and the structural plasticity of the receptor itself ( Figure 1 C).…”