Structures of the human cholecystokinin 1 (CCK1) receptor bound to Gs and Gq mimetic proteins provide insight into mechanisms of G protein selectivity

Abstract

G protein–coupled receptors (GPCRs) are critical regulators of cellular function acting via heterotrimeric G proteins as their primary transducers with individual GPCRs capable of pleiotropic coupling to multiple G proteins. Structural features governing G protein selectivity and promiscuity are currently unclear. Here, we used cryo-electron microscopy (cryo-EM) to determine structures of the cholecystokinin (CCK) type 1 receptor (CCK1R) bound to the CCK peptide agonist, CCK-8 and 2 distinct transducer proteins, its primary transducer Gq, and the more weakly coupled Gs. As seen with other Gq/11–GPCR complexes, the Gq–α5 helix (αH5) bound to a relatively narrow pocket in the CCK1R core. Surprisingly, the backbone of the CCK1R and volume of the G protein binding pocket were essentially equivalent when Gs was bound, with the Gs αH5 displaying a conformation that arises from “unwinding” of the far carboxyl-terminal residues, compared to canonically Gs coupled receptors. Thus, integrated changes in the conformations of both the receptor and G protein are likely to play critical roles in the promiscuous coupling of individual GPCRs.

Structures of signaling complexes of lipid receptors S1PR1 and S1PR5 reveal mechanisms of activation and drug recognition

“…Additionally, water-mediated interactions play an important role in activation of GPCRs as indicated by a molecular dynamics simulation study 25 and the high-resolution structures of GPCRs. 26 Therefore, water-mediated interactions may be involved in the contacts between siponimod and the receptor.…”

Discovery of a Positive Allosteric Modulator of Cholecystokinin Action at CCK1R in Normal and Elevated Cholesterol

“… Molecular models of Compound 1 bound to the CCK1R. Shown are molecular models of the docking of Compound 1 to the active CCK1R ( 11 ), following removal of the peptide agonist. The two poses depicted represent the two principal converged clusters based on their interaction patterns: the largest cluster (A) , and the cluster containing the highest scoring IFD pose (B) .…”

“…The recently solved CCK-occupied CCK1R complexed with Gs ( 11 ) was used as a starting point for the modeling since it had the best ligand-binding region resolution of the structures reported in that study. All molecules except for the receptor CCK1R (chain R) were deleted and CCK1R was prepared using the Maestro (Schrodinger, LLC) protein preparation wizard as follows: adding hydrogens, adding missing side chains, determining protonation states and side-chain orientation based on hydrogen bond optimization, removing the waters, and minimizing the structure using the OPLS4 force field.…”

“…The PAM action of Compound 1 was, at least partially, mediated by slowing the off-rate of CCK bound to CCK1R. Computational docking of Compound 1 to our recently reported high-resolution, active structure of CCK1R (11) yielded multiple potential poses. To probe the potential site of receptor interaction, we developed a photolabile probe based on the structure of Compound 1 to establish spatial approximations to the receptor.…”

Structure determination of GPCRs: cryo-EM compared with X-ray crystallography

“…In 2019 with the first dozen GPCR-G protein complexes solved [ 53 ] the average resolution was 3.76 Å with the best being 3.3 Å. In comparison, in the first six months of 2021, 48 GPCR-G protein cryo-EM structures were determined (21 unique receptors) with an average resolution of 3.11 Å (highest resolution, 1.95 Å) [ 54 ] and 16 structures with resolutions below 3 Å. The resolution of these structures is comparable to standard X-ray crystallography and has been achieved through further developments in cryo-EM technology [ 55 ].…”