Modulation of Constitutive Activity and Signaling Bias of the Ghrelin Receptor by Conformational Constraint in the Second Extracellular Loop

Mokrosiński, Jacek; Frimurer, Thomas M.; Sivertsen, Bjoern; Schwartz, Thue W.; Holst, Birgitte

doi:10.1074/jbc.m112.383240

Cited by 35 publications

(38 citation statements)

References 72 publications

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“…To assess whether the occurrence of the active complex in the absence of ligand is related to the high constitutive activity of the ghrelin receptor, we investigated the interaction between Gq and the A 204 E mutant of GHS-R1a. As is the case in cellular systems (17,25), the purified A 204 E mutant exhibits significantly decreased constitutive activity while it can be fully activated with MK0677 (SI Appendix, Fig. S9).…”

Section: Resultsmentioning

confidence: 99%

“…The observation that the inactive mutant is frozen in a basal inactive conformation, whereas the WT receptor oscillates between this same basal state and an active state, provides an additional piece of evidence for the model in which the absence of constitutive activity is associated with reduced conformational dynamics of GHS-R1a (25). Restriction of the conformational flexibility of the A 204 E mutant could result from an additional structural constraint introduced at the level of the e2 loop on substitution of the A 204 residue (25). Consistent with occurrence of the basal conformation as a major state, the inactive preassembled complex is the major species in the case of the ligandfree, constitutively inactive A 204 E mutant.…”

Section: Discussionmentioning

confidence: 99%

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Ghrelin receptor conformational dynamics regulate the transition from a preassembled to an active receptor:Gq complex

Damian

Mary

Maingot

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

118

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How G protein-coupled receptor conformational dynamics control G protein coupling to trigger signaling is a key but still open question. We addressed this question with a model system composed of the purified ghrelin receptor assembled into lipid discs. Combining receptor labeling through genetic incorporation of unnatural amino acids, lanthanide resonance energy transfer, and normal mode analyses, we directly demonstrate the occurrence of two distinct receptor:Gq assemblies with different geometries whose relative populations parallel the activation state of the receptor. The first of these assemblies is a preassembled complex with the receptor in its basal conformation. This complex is specific of Gq and is not observed with Gi. The second one is an active assembly in which the receptor in its active conformation triggers G protein activation. The active complex is present even in the absence of agonist, in a direct relationship with the high constitutive activity of the ghrelin receptor. These data provide direct evidence of a mechanism for ghrelin receptor-mediated Gq signaling in which transition of the receptor from an inactive to an active conformation is accompanied by a rearrangement of a preassembled receptor:G protein complex, ultimately leading to G protein activation and signaling.GPCR | G protein | preassembly | conformation dynamics | signaling G protein-coupled receptors (GPCRs), one of the largest cell surface receptor families, are involved in many cellular signaling processes (1). Based on this property, as well as their importance as drug targets, the molecular aspects of GPCR functioning have been extensively investigated. In particular, coupling to heterotrimeric G proteins has been the focus of numerous studies. Indeed, delineating the molecular mechanisms responsible for receptor:G protein interaction is absolutely required to better understand how signaling is controlled. Recent years have seen spectacular advances that have culminated in elucidation of the 3D structure of the β 2 -adrenergic receptor:Gs complex (2). Nevertheless, the need for further progress remains, in particular to fully understand the dynamics of this interaction. This is a crucial question, given that how the receptor interacts with its G protein partner governs signaling, and thus biological and pathophysiological responses.To date, two different models for GPCR:G protein interaction have been proposed: collision coupling and preassembly. Originally, it was proposed that receptors and G proteins couple by collision (3, 4). One of the main features of this model is that only activated receptors interact with G proteins. Since then, alternative models of signaling have been developed. One of these, the preassembly model, proposes that the receptor and the G protein make a complex even in the absence of agonist (5-8).

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Ghrelin receptor conformational dynamics regulate the transition from a preassembled to an active receptor:Gq complex

Damian

Mary

Maingot

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

118

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“…Recently, another interesting hypothesis was suggested based on the finding that the GHSR1a receptor has significant basal activity [224] and that the GHSR knockout mice had a higher seizure threshold than their wild-type littermates [225]: an endogenous agonist can have anticonvulsant action by reducing the activity of the constitutively active receptor with a combination of inverse agonism and desensitization/internalization of the receptor [225]. This hypothesis should be tested by newly developed inverse agonists of the GHSR1a receptor [226,227].…”

Section: Ghrelinmentioning

confidence: 99%

Receptors of Peptides as Therapeutic Targets in Epilepsy Research

Dobolyi¹,

Kékesi²,

Juhász³

et al. 2014

CMC

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Neuropeptides are signaling molecules participating in the modulation of synaptic transmission. Neuropeptides are stored in dense core synaptic vesicles, the release of which requires profound excitation. Only in the extracellular space, neuropeptides act on G-protein coupled receptors to exert a relatively slow action both pre-and postsynaptically. Consequently, neuropeptide modulators are ideal candidates to influence epileptic tissue overexcited during seizures. Indeed, a number of neuropeptides have been implicated in epilepsy and many of them are considered to have endogenous neuroprotective actions. Neuropeptides, present in the hippocampus, the most frequent focus of seizures in temporal lobe epilepsy, received the largest attention as potential anti-epileptic substances. Hippocampal neuropeptides, somatostatin, neuropeptide Y, galanin, dynorphin, enkephalin, substance P, cholecystokinin, vasoactive intestinal polypeptide, and some neuropeptides, which are also hormones such as ghrelin, angiotensins, corticotropin-releasing hormone, adrenocorticotropin, thyrotropin-releasing hormone, oxytocin and vasopressin involved in epilepsy are discussed in the review article. Oral application of neuropeptides as drugs is typically not efficient because of low bioavailability: rapid degradation and insufficient penetration through the blood-brain barrier. Recent progress in the development of non-peptide agonists and antagonists of neuropeptide receptors as well as gene therapeutic approaches leading to the local production of neuropeptides within the central nervous system will also be discussed.

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“…The spectrum of these discrete physiological responses observed following biochemical separation of G protein from ␤-arrestin activity suggest that the signaling bias obtained by their pharmacological separation will provide a blueprint for designing new generations of selective therapies (2). Recent studies indicate that the growth hormone secretagogue receptor GHSR1a binds ␤-arrestin following treatment with the hormone ghrelin (3)(4)(5). The GHSR1a ghrelin receptor belongs to a small family of GPCRs for peptide hormones and neuropeptides (6), and, by increasing dopamine release (7)(8)(9), it mediates the reinforcement of natural rewards, such as food (10 -12), and the reinforcement of chemical rewards, such as alcohol (13) and drugs of abuse (9).…”

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confidence: 99%

G Protein and β-Arrestin Signaling Bias at the Ghrelin Receptor

Evron

Peterson

Urs

et al. 2014

Journal of Biological Chemistry

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Background:The G protein coupled receptor GHSR1a mediates feeding and addictive behaviors. Results: Mutagenesis of the second intracellular loop of GHSR1a generates biased receptors, favoring distinct signaling events. Conclusion: Receptor conformations that support signaling bias at the wild-type receptor should exist. Significance: Recapitulating signaling bias at GHSR1a may facilitate the identification of novel selective therapies to treat addiction.

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Modulation of Constitutive Activity and Signaling Bias of the Ghrelin Receptor by Conformational Constraint in the Second Extracellular Loop

Cited by 35 publications

References 72 publications

Ghrelin receptor conformational dynamics regulate the transition from a preassembled to an active receptor:Gq complex

Ghrelin receptor conformational dynamics regulate the transition from a preassembled to an active receptor:Gq complex

Receptors of Peptides as Therapeutic Targets in Epilepsy Research

G Protein and β-Arrestin Signaling Bias at the Ghrelin Receptor

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