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1
Jastrzebska, Beata, Yaroslav Tsybovsky, and Krzysztof Palczewski. "Complexes between photoactivated rhodopsin and transducin: progress and questions." Biochemical Journal 428, no. 1 (April 28, 2010): 1–10. http://dx.doi.org/10.1042/bj20100270.
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Activation of GPCRs (G-protein-coupled receptors) leads to conformational changes that ultimately initiate signal transduction. Activated GPCRs transiently combine with and activate heterotrimeric G-proteins resulting in GTP replacement of GDP on the G-protein α subunit. Both the detailed structural changes essential for productive GDP/GTP exchange on the G-protein α subunit and the structure of the GPCR–G-protein complex itself have yet to be elucidated. Nevertheless, transient GPCR–G-protein complexes can be trapped by nucleotide depletion, yielding an empty-nucleotide G-protein–GPCR complex that can be isolated. Whereas early biochemical studies indicated formation of a complex between G-protein and activated receptor only, more recent results suggest that G-protein can bind to pre-activated states of receptor or even couple transiently to non-activated receptor to facilitate rapid responses to stimuli. Efficient and reproducible formation of physiologically relevant, conformationally homogenous GPCR–G-protein complexes is a prerequisite for structural studies designed to address these possibilities.
2
Pellissier, Lucie P., Gaël Barthet, Florence Gaven, Elisabeth Cassier, Eric Trinquet, Jean-Philippe Pin, Philippe Marin, et al. "G Protein Activation by Serotonin Type 4 Receptor Dimers." Journal of Biological Chemistry 286, no. 12 (January 19, 2011): 9985–97. http://dx.doi.org/10.1074/jbc.m110.201939.
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The discovery that class C G protein-coupled receptors (GPCRs) function as obligatory dimeric entities has generated major interest in GPCR oligomerization. Oligomerization now appears to be a common feature among all GPCR classes. However, the functional significance of this process remains unclear because, in vitro, some monomeric GPCRs, such as rhodopsin and β2-adrenergic receptors, activate G proteins. By using wild type and mutant serotonin type 4 receptors (5-HT4Rs) (including a 5-HT4-RASSL) expressed in COS-7 cells as models of class A GPCRs, we show that activation of one protomer in a dimer was sufficient to stimulate G proteins. However, coupling efficiency was 2 times higher when both protomers were activated. Expression of combinations of 5-HT4, in which both protomers were able to bind to agonists but only one could couple to G proteins, suggested that upon agonist occupancy, protomers did not independently couple to G proteins but rather that only one G protein was activated. Coupling of a single heterotrimeric Gs protein to a receptor dimer was further confirmed in vitro, using the purified recombinant WT RASSL 5-HT4R obligatory heterodimer. These results, together with previous findings, demonstrate that, differently from class C GPCR dimers, class A GPCR dimers have pleiotropic activation mechanisms.
3
Bhattacharya, M., A. V. Babwah, and S. S. G. Ferguson. "Small GTP-binding protein-coupled receptors." Biochemical Society Transactions 32, no. 6 (October 26, 2004): 1040–44. http://dx.doi.org/10.1042/bst0321040.
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Heterotrimeric GPCRs (G-protein-coupled receptors) form the largest group of integral membrane receptor proteins and mediate diverse physiological processes. In addition to signalling via heterotrimeric G-proteins, GPCRs can also signal by interacting with various small G-proteins to regulate downstream effector pathways. The small G-protein superfamily is structurally classified into at least five families: the Ras, Rho/Rac/cdc42, Rab, Sar1/Arf and Ran families. They are monomeric G-proteins with molecular masses over the range 20–30 kDa, which function as molecular switches to control many eukaryotic cell functions. Several studies have provided evidence of crosstalk between GPCRs and small G-proteins. It is well documented that GPCR signalling through heterotrimeric G-proteins can lead to the activation of Ras and Rho GTPases. In addition, RhoA, Rabs, ARFs and ARF GEFs (guanine nucleotide-exchange factors) can associate directly with GPCRs, and GPCRs may also function as GEFs for small GTPases. In this review, we summarize the recent progress made in understanding the interaction between GPCRs and small GTPases, focusing on understanding how the association of small G-proteins with GPCRs and GPCR-regulatory proteins may influence GPCR signalling and intracellular trafficking.
4
Erlandson, Sarah C., Conor McMahon, and Andrew C. Kruse. "Structural Basis for G Protein–Coupled Receptor Signaling." Annual Review of Biophysics 47, no. 1 (May 20, 2018): 1–18. http://dx.doi.org/10.1146/annurev-biophys-070317-032931.
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G protein–coupled receptors (GPCRs), which mediate processes as diverse as olfaction and maintenance of metabolic homeostasis, have become the single most effective class of therapeutic drug targets. As a result, understanding the molecular basis for their activity is of paramount importance. Recent technological advances have made GPCR structural biology increasingly tractable, offering views of these receptors in unprecedented atomic detail. Structural and biophysical data have shown that GPCRs function as complex allosteric machines, communicating ligand-binding events through conformational change. Changes in receptor conformation lead to activation of effector proteins, such as G proteins and arrestins, which are themselves conformational switches. Here, we review how structural biology has illuminated the agonist-induced cascade of conformational changes that culminate in a cellular response to GPCR activation.
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Hay, Debbie L., Christopher S. Walker, Joseph J. Gingell, Graham Ladds, Christopher A. Reynolds, and David R. Poyner. "Receptor activity-modifying proteins; multifunctional G protein-coupled receptor accessory proteins." Biochemical Society Transactions 44, no. 2 (April 11, 2016): 568–73. http://dx.doi.org/10.1042/bst20150237.
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Receptor activity-modifying proteins (RAMPs) are single pass membrane proteins initially identified by their ability to determine the pharmacology of the calcitonin receptor-like receptor (CLR), a family B G protein-coupled receptor (GPCR). It is now known that RAMPs can interact with a much wider range of GPCRs. This review considers recent developments on the structure of the complexes formed between the extracellular domains (ECDs) of CLR and RAMP1 or RAMP2 as these provide insights as to how the RAMPs direct ligand binding. The range of RAMP interactions is also considered; RAMPs can interact with numerous family B GPCRs as well as examples of family A and family C GPCRs. They influence receptor expression at the cell surface, trafficking, ligand binding and G protein coupling. The GPCR–RAMP interface offers opportunities for drug targeting, illustrated by examples of drugs developed for migraine.
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Gupte, Tejas M., Rabia U. Malik, Ruth F. Sommese, Michael Ritt, and Sivaraj Sivaramakrishnan. "Priming GPCR signaling through the synergistic effect of two G proteins." Proceedings of the National Academy of Sciences 114, no. 14 (March 21, 2017): 3756–61. http://dx.doi.org/10.1073/pnas.1617232114.
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Although individual G-protein–coupled receptors (GPCRs) are known to activate one or more G proteins, the GPCR–G-protein interaction is viewed as a bimolecular event involving the formation of a ternary ligand–GPCR–G-protein complex. Here, we present evidence that individual GPCR–G-protein interactions can reinforce each other to enhance signaling through canonical downstream second messengers, a phenomenon we term “GPCR priming.” Specifically, we find that the presence of noncognate Gq protein enhances cAMP stimulated by two Gs-coupled receptors, β2-adrenergic receptor (β2-AR) and D1 dopamine receptor (D1-R). Reciprocally, Gs enhances IP1 through vasopressin receptor (V1A-R) but not α1 adrenergic receptor (α1-AR), suggesting that GPCR priming is a receptor-specific phenomenon. The C terminus of either the Gαs or Gαq subunit is sufficient to enhance Gα subunit activation and cAMP levels. Interaction of Gαs or Gαq C termini with the GPCR increases signaling potency, suggesting an altered GPCR conformation as the underlying basis for GPCR priming. We propose three parallel mechanisms involving (i) sequential G-protein interactions at the cognate site, (ii) G-protein interactions at distinct allosteric and cognate sites on the GPCR, and (iii) asymmetric GPCR dimers. GPCR priming suggests another layer of regulation in the classic GPCR ternary-complex model, with broad implications for the multiplicity inherent in signaling networks.
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N'Diaye, Elsa-Noah, Aylin C. Hanyaloglu, Kimberly K. Kajihara, Manojkumar A. Puthenveedu, Ping Wu, Mark von Zastrow, and Eric J. Brown. "The Ubiquitin-like Protein PLIC-2 Is a Negative Regulator of G Protein-coupled Receptor Endocytosis." Molecular Biology of the Cell 19, no. 3 (March 2008): 1252–60. http://dx.doi.org/10.1091/mbc.e07-08-0775.
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The activity of many signaling receptors is regulated by their endocytosis via clathrin-coated pits (CCPs). For G protein-coupled receptors (GPCRs), recruitment of the adaptor protein arrestin to activated receptors is thought to be sufficient to drive GPCR clustering in CCPs and subsequent endocytosis. We have identified an unprecedented role for the ubiquitin-like protein PLIC-2 as a negative regulator of GPCR endocytosis. Protein Linking IAP to Cytoskeleton (PLIC)-2 overexpression delayed ligand-induced endocytosis of two GPCRs: the V2 vasopressin receptor and β-2 adrenergic receptor, without affecting endocytosis of the transferrin or epidermal growth factor receptor. The closely related isoform PLIC-1 did not affect receptor endocytosis. PLIC-2 specifically inhibited GPCR concentration in CCPs, without affecting membrane recruitment of arrestin-3 to activated receptors or its cellular levels. Depletion of cellular PLIC-2 accelerated GPCR endocytosis, confirming its regulatory function at endogenous levels. The ubiquitin-like domain of PLIC-2, a ligand for ubiquitin-interacting motifs (UIMs), was required for endocytic inhibition. Interestingly, the UIM-containing endocytic adaptors epidermal growth factor receptor protein substrate 15 and Epsin exhibited preferential binding to PLIC-2 over PLIC-1. This differential interaction may underlie PLIC-2 specific effect on GPCR endocytosis. Identification of a negative regulator of GPCR clustering reveals a new function of ubiquitin-like proteins and highlights a cellular requirement for exquisite regulation of receptor dynamics.
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Ayoub, Mohammed Akli, and Ranjit Vijayan. "Hemorphins Targeting G Protein-Coupled Receptors." Pharmaceuticals 14, no. 3 (March 7, 2021): 225. http://dx.doi.org/10.3390/ph14030225.
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Hemorphins are short peptides produced by the proteolysis of the beta subunit of hemoglobin. These peptides have diverse physiological effects especially in the nervous and the renin-angiotensin systems. Such effects occur through the modulation of a diverse range of proteins including enzymes and receptors. In this review, we focus on pharmacological and functional targeting of G protein-coupled receptors (GPCRs) by hemorphins and their implication in physiology and pathophysiology. Among GPCRs, the opioid receptors constitute the first set of targets of hemorphins with implication in analgesia. Subsequently, several other GPCRs have been reported to be directly or indirectly involved in hemorphins’ action. This includes the receptors for angiotensin II, oxytocin, bombesin, and bradykinin, as well as the human MAS-related G protein-coupled receptor X1. Interestingly, both orthosteric activation and allosteric modulation of GPCRs by hemorphins have been reported. This review links hemorphins with GPCR pharmacology and signaling, supporting the implication of GPCRs in hemorphins’ effects. Thus, this aids a better understanding of the molecular basis of the action of hemorphins and further demonstrates that hemorphin-GPCR axis constitutes a valid target for therapeutic intervention in different systems.
9
Vidad, Ashley Ryan, Stephen Macaspac, and Ho Leung Ng. "Locating ligand binding sites in G-protein coupled receptors using combined information from docking and sequence conservation." PeerJ 9 (September 24, 2021): e12219. http://dx.doi.org/10.7717/peerj.12219.
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GPCRs (G-protein coupled receptors) are the largest family of drug targets and share a conserved structure. Binding sites are unknown for many important GPCR ligands due to the difficulties of GPCR recombinant expression, biochemistry, and crystallography. We describe our approach, ConDockSite, for predicting ligand binding sites in class A GPCRs using combined information from surface conservation and docking, starting from crystal structures or homology models. We demonstrate the effectiveness of ConDockSite on crystallized class A GPCRs such as the beta2 adrenergic and A2A adenosine receptors. We also demonstrate that ConDockSite successfully predicts ligand binding sites from high-quality homology models. Finally, we apply ConDockSite to predict the ligand binding sites on a structurally uncharacterized GPCR, GPER, the G-protein coupled estrogen receptor. Most of the sites predicted by ConDockSite match those found in other independent modeling studies. ConDockSite predicts that four ligands bind to a common location on GPER at a site deep in the receptor cleft. Incorporating sequence conservation information in ConDockSite overcomes errors introduced from physics-based scoring functions and homology modeling.
10
Whorton, Matthew R., Michael P. Bokoch, Søren G. F. Rasmussen, Bo Huang, Richard N. Zare, Brian Kobilka, and Roger K. Sunahara. "A monomeric G protein-coupled receptor isolated in a high-density lipoprotein particle efficiently activates its G protein." Proceedings of the National Academy of Sciences 104, no. 18 (April 23, 2007): 7682–87. http://dx.doi.org/10.1073/pnas.0611448104.
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G protein-coupled receptors (GPCRs) respond to a diverse array of ligands, mediating cellular responses to hormones and neurotransmitters, as well as the senses of smell and taste. The structures of the GPCR rhodopsin and several G proteins have been determined by x-ray crystallography, yet the organization of the signaling complex between GPCRs and G proteins is poorly understood. The observations that some GPCRs are obligate heterodimers, and that many GPCRs form both homo- and heterodimers, has led to speculation that GPCR dimers may be required for efficient activation of G proteins. However, technical limitations have precluded a definitive analysis of G protein coupling to monomeric GPCRs in a biochemically defined and membrane-bound system. Here we demonstrate that a prototypical GPCR, the β2-adrenergic receptor (β2AR), can be incorporated into a reconstituted high-density lipoprotein (rHDL) phospholipid bilayer particle together with the stimulatory heterotrimeric G protein, Gs. Single-molecule fluorescence imaging and FRET analysis demonstrate that a single β2AR is incorporated per rHDL particle. The monomeric β2AR efficiently activates Gs and displays GTP-sensitive allosteric ligand-binding properties. These data suggest that a monomeric receptor in a lipid bilayer is the minimal functional unit necessary for signaling, and that the cooperativity of agonist binding is due to G protein association with a receptor monomer and not receptor oligomerization.
11
Maggio, Roberto, Irene Fasciani, Francesco Petragnano, Maria Francesca Coppolino, Marco Scarselli, and Mario Rossi. "Unraveling the Functional Significance of Unstructured Regions in G Protein-Coupled Receptors." Biomolecules 13, no. 10 (September 22, 2023): 1431. http://dx.doi.org/10.3390/biom13101431.
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Unstructured regions in functional proteins have gained attention in recent years due to advancements in informatics tools and biophysical methods. G protein-coupled receptors (GPCRs), a large family of cell surface receptors, contain unstructured regions in the form of the i3 loop and C-terminus. This review provides an overview of the functional significance of these regions in GPCRs. GPCRs transmit signals from the extracellular environment to the cell interior, regulating various physiological processes. The i3 loop, located between the fifth and sixth transmembrane helices, and the C-terminus, connected to the seventh transmembrane helix, are determinant of interactions with G proteins and with other intracellular partners such as arrestins. Recent studies demonstrate that the i3 loop and C-terminus play critical roles in allosterically regulating GPCR activation. They can act as autoregulators, adopting conformations that, by restricting G protein access, modulate receptor coupling specificity. The length and unstructured nature of the i3 loop and C-terminus provide unique advantages in GPCR interactions with intracellular protein partners. They act as “fishing lines”, expanding the radius of interaction and enabling GPCRs to tether scaffolding proteins, thus facilitating receptor stability during cell membrane movements. Additionally, the i3 loop may be involved in domain swapping between GPCRs, generating novel receptor dimers with distinct binding and coupling characteristics. Overall, the i3 loop and C-terminus are now widely recognized as crucial elements in GPCR function and regulation. Understanding their functional roles enhances our comprehension of GPCR structure and signaling complexity and holds promise for advancements in receptor pharmacology and drug development.
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Dziedzicka-Wasylewska, Marta, Agnieszka Polit, Ewa Błasiak, and Agata Faron-Górecka. "G Protein-Coupled Receptor Dimerization—What Next?" International Journal of Molecular Sciences 25, no. 6 (March 7, 2024): 3089. http://dx.doi.org/10.3390/ijms25063089.
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Numerous studies highlight the therapeutic potential of G protein-coupled receptor (GPCR) heterodimers, emphasizing their significance in various pathological contexts. Despite extensive basic research and promising outcomes in animal models, the translation of GPCR heterodimer-targeting drugs into clinical use remains limited. The complexities of in vivo conditions, particularly within thecomplex central nervous system, pose challenges in fully replicating physiological environments, hindering clinical success. This review discusses examples of the most studied heterodimers, their involvement in nervous system pathology, and the available data on their potential ligands. In addition, this review highlights the intricate interplay between lipids and GPCRs as a potential key factor in understanding the complexity of cell signaling. The multifaceted role of lipids in modulating the dynamics of GPCR dimerization is explored, shedding light on the elaborate molecular mechanisms governing these interactions.
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Luttrell, Louis M., and Robert J. Lefkowitz. "The role of β-arrestins in the termination and transduction of G-protein-coupled receptor signals." Journal of Cell Science 115, no. 3 (February 1, 2002): 455–65. http://dx.doi.org/10.1242/jcs.115.3.455.
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β-arrestins are versatile adapter proteins that form complexes with most G-protein-coupled receptors (GPCRs) following agonist binding and phosphorylation of receptors by G-protein-coupled receptor kinases (GRKs). They play a central role in the interrelated processes of homologous desensitization and GPCR sequestration, which lead to the termination of G protein activation. β-arrestin binding to GPCRs both uncouples receptors from heterotrimeric G proteins and targets them to clathrin-coated pits for endocytosis. Recent data suggest that β-arrestins also function as GPCR signal transducers. They can form complexes with several signaling proteins,including Src family tyrosine kinases and components of the ERK1/2 and JNK3 MAP kinase cascades. By recruiting these kinases to agonist-occupied GPCRs,β-arrestins confer distinct signaling activities upon the receptor.β-arrestin-Src complexes have been proposed to modulate GPCR endocytosis,to trigger ERK1/2 activation and to mediate neutrophil degranulation. By acting as scaffolds for the ERK1/2 and JNK3 cascades, β-arrestins both facilitate GPCR-stimulated MAP kinase activation and target active MAP kinases to specific locations within the cell. Thus, their binding to GPCRs might initiate a second wave of signaling and represent a novel mechanism of GPCR signal transduction.
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Yan, Huan, Jingling Zhang, Kam-Tong Leung, Kwok-Wai Lo, Jun Yu, Ka-Fai To, and Wei Kang. "An Update of G-Protein-Coupled Receptor Signaling and Its Deregulation in Gastric Carcinogenesis." Cancers 15, no. 3 (January 25, 2023): 736. http://dx.doi.org/10.3390/cancers15030736.
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G-protein-coupled receptors (GPCRs) belong to a cell surface receptor superfamily responding to a wide range of external signals. The binding of extracellular ligands to GPCRs activates a heterotrimeric G protein and triggers the production of numerous secondary messengers, which transduce the extracellular signals into cellular responses. GPCR signaling is crucial and imperative for maintaining normal tissue homeostasis. High-throughput sequencing analyses revealed the occurrence of the genetic aberrations of GPCRs and G proteins in multiple malignancies. The altered GPCRs/G proteins serve as valuable biomarkers for early diagnosis, prognostic prediction, and pharmacological targets. Furthermore, the dysregulation of GPCR signaling contributes to tumor initiation and development. In this review, we have summarized the research progress of GPCRs and highlighted their mechanisms in gastric cancer (GC). The aberrant activation of GPCRs promotes GC cell proliferation and metastasis, remodels the tumor microenvironment, and boosts immune escape. Through deep investigation, novel therapeutic strategies for targeting GPCR activation have been developed, and the final aim is to eliminate GPCR-driven gastric carcinogenesis.
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Katanaev, Vladimir L., and Matey Chornomorets. "Kinetic diversity in G-protein-coupled receptor signalling." Biochemical Journal 401, no. 2 (December 21, 2006): 485–95. http://dx.doi.org/10.1042/bj20060517.
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The majority of intracellular signalling cascades in higher eukaryotes are initiated by GPCRs (G-protein-coupled receptors). Hundreds of GPCRs signal through a handful of trimeric G-proteins, raising the issue of signal specificity. In the present paper, we illustrate a simple kinetic model of G-protein signalling. This model shows that stable production of significant amounts of free GαGTP (GTP-bound Gα subunit) and βγ is only one of multiple modes of behaviour of the G-protein system upon activation. Other modes, previously uncharacterized, are sustained production of βγ without significant levels of GαGTP and transient production of GαGTP with sustained βγ. The system can flip between different modes upon changes in conditions. This model demonstrates further that the negative feedback of receptor uncoupling or internalization, when combined with a positive feedback within the G-protein cycle, under a broad range of conditions results not in termination of the response but in relaxed oscillations in GPCR signalling. This variety of G-protein responses may serve to encode signal specificity in GPCR signal transduction.
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Rivero-Müller, Adolfo, Yen-Yin Chou, Inhae Ji, Svetlana Lajic, Aylin C. Hanyaloglu, Kim Jonas, Nafis Rahman, Tae H. Ji, and Ilpo Huhtaniemi. "Rescue of defective G protein–coupled receptor function in vivo by intermolecular cooperation." Proceedings of the National Academy of Sciences 107, no. 5 (January 11, 2010): 2319–24. http://dx.doi.org/10.1073/pnas.0906695106.
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G protein–coupled receptors (GPCRs) are ubiquitous mediators of signaling of hormones, neurotransmitters, and sensing. The old dogma is that a one ligand/one receptor complex constitutes the functional unit of GPCR signaling. However, there is mounting evidence that some GPCRs form dimers or oligomers during their biosynthesis, activation, inactivation, and/or internalization. This evidence has been obtained exclusively from cell culture experiments, and proof for the physiological significance of GPCR di/oligomerization in vivo is still missing. Using the mouse luteinizing hormone receptor (LHR) as a model GPCR, we demonstrate that transgenic mice coexpressing binding-deficient and signaling-deficient forms of LHR can reestablish normal LH actions through intermolecular functional complementation of the mutant receptors in the absence of functional wild-type receptors. These results provide compelling in vivo evidence for the physiological relevance of intermolecular cooperation in GPCR signaling.
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Chini, Bice, and Marco Parenti. "G-protein-coupled receptors, cholesterol and palmitoylation: facts about fats." Journal of Molecular Endocrinology 42, no. 5 (January 8, 2009): 371–79. http://dx.doi.org/10.1677/jme-08-0114.
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G-protein-coupled receptors (GPCRs) are integral membrane proteins, hence it is not surprising that a number of their structural and functional features are modulated by both proteins and lipids. The impact of interacting proteins and lipids on the assembly and signalling of GPCRs has been extensively investigated over the last 20–30 years, and a further impetus has been given by the proposal that GPCRs and/or their immediate signalling partners (G proteins) can partition within plasma membrane domains, termed rafts and caveolae, enriched in glycosphingolipids and cholesterol. The high content of these specific lipids, in particular of cholesterol, in the vicinity of GPCR transmembranes can affect GPCR structure and/or function. In addition, most GPCRs are post-translationally modified with one or more palmitic acid(s), a 16-carbon saturated fatty acid, covalently bound to cysteine(s) localised in the carboxyl-terminal cytoplasmic tail. The insertion of palmitate into the cytoplasmic leaflet of the plasma membrane can create a fourth loop, thus profoundly affecting GPCR structure and hence the interactions with intracellular partner proteins. This review briefly highlights how lipids of the membrane and the receptor themselves can influence GPCR organisation and functioning.
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Koval, Alexey, and Vladimir L. Katanaev. "Wnt3a stimulation elicits G-protein-coupled receptor properties of mammalian Frizzled proteins." Biochemical Journal 433, no. 3 (January 14, 2011): 435–40. http://dx.doi.org/10.1042/bj20101878.
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Receptors of the Fz (Frizzled) family initiate Wnt ligand-dependent signalling controlling multiple steps in organism development and carcinogenesis. Fz proteins possess seven transmembrane domains, and their signalling depends on heterotrimeric G-proteins in various organisms; however, Fz proteins constitute a distinct group within the GPCR (G-protein-coupled receptor) superfamily, and Fz signalling can be G-protein-independent in some experimental setups, leading to concerns about the GPCR nature of these proteins. In the present study, we demonstrate that mammalian Fz proteins act as GPCRs on heterotrimeric Go/i proteins. Addition of the Wnt3a ligand to rat brain membranes or cultured cells elicits Fz-dependent guanine-nucleotide exchange on Go/i proteins. These responses were sensitive to a Wnt antagonist and to pertussis toxin, which decouples the Go/i proteins from their receptors through covalent modification. The results of the present study provide the long-awaited biochemical proof of the GPCR nature of Fz receptors.
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Cant, Sarah H., and Julie A. Pitcher. "G Protein-coupled Receptor Kinase 2–mediated Phosphorylation of Ezrin Is Required for G Protein-coupled Receptor–dependent Reorganization of the Actin Cytoskeleton." Molecular Biology of the Cell 16, no. 7 (July 2005): 3088–99. http://dx.doi.org/10.1091/mbc.e04-10-0877.
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G protein-coupled receptor kinase 2 (GRK2) phosphorylates and desensitizes activated G protein-coupled receptors (GPCRs). Here, we identify ezrin as a novel non-GPCR substrate of GRK2. GRK2 phosphorylates glutathione S-transferase (GST)-ezrin, but not an ezrin fusion protein lacking threonine 567 (T567), in vitro. These results suggest that T567, the regulatory phosphorylation site responsible for maintaining ezrin in its active conformation, represents the principle site of GRK2-mediated phosphorylation. Two lines of evidence indicate that GRK2-mediated ezrin-radixinmoesin (ERM) phosphorylation serves to link GPCR activation to cytoskeletal reorganization. First, in Hep2 cells muscarinic M1 receptor (M1MR) activation causes membrane ruffling. This ruffling response is ERM dependent and is accompanied by ERM phosphorylation. Inhibition of GRK2, but not rho kinase or protein kinase C, prevents ERM phosphorylation and membrane ruffling. Second, agonist-induced internalization of the β2-adrenergic receptor (β2AR) and M1MR is accompanied by ERM phosphorylation and localization of phosphorylated ERM to receptor-containing endocytic vesicles. The colocalization of internalized β2AR and phosphorylated ERM is not dependent on Na+/H+ exchanger regulatory factor binding to the β2AR. Inhibition of ezrin function impedes β2AR internalization, further linking GPCR activation, GRK activity, and ezrin function. Overall, our results suggest that GRK2 serves not only to attenuate but also to transduce GPCR-mediated signals.
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Shiraishi, Akira, Toshimi Okuda, Natsuko Miyasaka, Tomohiro Osugi, Yasushi Okuno, Jun Inoue, and Honoo Satake. "Repertoires of G protein-coupled receptors for Ciona-specific neuropeptides." Proceedings of the National Academy of Sciences 116, no. 16 (April 1, 2019): 7847–56. http://dx.doi.org/10.1073/pnas.1816640116.
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Neuropeptides play pivotal roles in various biological events in the nervous, neuroendocrine, and endocrine systems, and are correlated with both physiological functions and unique behavioral traits of animals. Elucidation of functional interaction between neuropeptides and receptors is a crucial step for the verification of their biological roles and evolutionary processes. However, most receptors for novel peptides remain to be identified. Here, we show the identification of multiple G protein-coupled receptors (GPCRs) for species-specific neuropeptides of the vertebrate sister group, Ciona intestinalis Type A, by combining machine learning and experimental validation. We developed an original peptide descriptor-incorporated support vector machine and used it to predict 22 neuropeptide–GPCR pairs. Of note, signaling assays of the predicted pairs identified 1 homologous and 11 Ciona-specific neuropeptide–GPCR pairs for a 41% hit rate: the respective GPCRs for Ci-GALP, Ci-NTLP-2, Ci-LF-1, Ci-LF-2, Ci-LF-5, Ci-LF-6, Ci-LF-7, Ci-LF-8, Ci-YFV-1, and Ci-YFV-3. Interestingly, molecular phylogenetic tree analysis revealed that these receptors, excluding the Ci-GALP receptor, were evolutionarily unrelated to any other known peptide GPCRs, confirming that these GPCRs constitute unprecedented neuropeptide receptor clusters. Altogether, these results verified the neuropeptide–GPCR pairs in the protochordate and evolutionary lineages of neuropeptide GPCRs, and pave the way for investigating the endogenous roles of novel neuropeptides in the closest relatives of vertebrates and the evolutionary processes of neuropeptidergic systems throughout chordates. In addition, the present study also indicates the versatility of the machine-learning–assisted strategy for the identification of novel peptide–receptor pairs in various organisms.
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Southern, Craig, Jennifer M. Cook, Zaynab Neetoo-Isseljee, Debra L. Taylor, Catherine A. Kettleborough, Andy Merritt, Daniel L. Bassoni, et al. "Screening β-Arrestin Recruitment for the Identification of Natural Ligands for Orphan G-Protein–Coupled Receptors." Journal of Biomolecular Screening 18, no. 5 (February 8, 2013): 599–609. http://dx.doi.org/10.1177/1087057113475480.
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A variety of G-protein–coupled receptor (GPCR) screening technologies have successfully partnered a number of GPCRs with their cognate ligands. GPCR-mediated β-arrestin recruitment is now recognized as a distinct intracellular signaling pathway, and ligand-receptor interactions may show a bias toward β-arrestin over classical GPCR signaling pathways. We hypothesized that the failure to identify native ligands for the remaining orphan GPCRs may be a consequence of biased β-arrestin signaling. To investigate this, we assembled 10 500 candidate ligands and screened 82 GPCRs using PathHunter β-arrestin recruitment technology. High-quality screening assays were validated by the inclusion of liganded receptors and the detection and confirmation of these established ligand-receptor pairings. We describe a candidate endogenous orphan GPCR ligand and a number of novel surrogate ligands. However, for the majority of orphan receptors studied, measurement of β-arrestin recruitment did not lead to the identification of cognate ligands from our screening sets. β-Arrestin recruitment represents a robust GPCR screening technology, and ligand-biased signaling is emerging as a therapeutically exploitable feature of GPCR biology. The identification of cognate ligands for the orphan GPCRs and the extent to which receptors may exist to preferentially signal through β-arrestin in response to their native ligand remain to be determined.
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Van Eps, Ned, Christian Altenbach, Lydia N. Caro, Naomi R. Latorraca, Scott A. Hollingsworth, Ron O. Dror, Oliver P. Ernst, and Wayne L. Hubbell. "Gi- and Gs-coupled GPCRs show different modes of G-protein binding." Proceedings of the National Academy of Sciences 115, no. 10 (February 20, 2018): 2383–88. http://dx.doi.org/10.1073/pnas.1721896115.
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More than two decades ago, the activation mechanism for the membrane-bound photoreceptor and prototypical G protein-coupled receptor (GPCR) rhodopsin was uncovered. Upon light-induced changes in ligand–receptor interaction, movement of specific transmembrane helices within the receptor opens a crevice at the cytoplasmic surface, allowing for coupling of heterotrimeric guanine nucleotide-binding proteins (G proteins). The general features of this activation mechanism are conserved across the GPCR superfamily. Nevertheless, GPCRs have selectivity for distinct G-protein family members, but the mechanism of selectivity remains elusive. Structures of GPCRs in complex with the stimulatory G protein, Gs, and an accessory nanobody to stabilize the complex have been reported, providing information on the intermolecular interactions. However, to reveal the structural selectivity filters, it will be necessary to determine GPCR–G protein structures involving other G-protein subtypes. In addition, it is important to obtain structures in the absence of a nanobody that may influence the structure. Here, we present a model for a rhodopsin–G protein complex derived from intermolecular distance constraints between the activated receptor and the inhibitory G protein, Gi, using electron paramagnetic resonance spectroscopy and spin-labeling methodologies. Molecular dynamics simulations demonstrated the overall stability of the modeled complex. In the rhodopsin–Gi complex, Gi engages rhodopsin in a manner distinct from previous GPCR–Gs structures, providing insight into specificity determinants.
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Bi, Tianyi, and Pengyu Wei. "G proteins: introduction of its history, structure, function, and drug development." Theoretical and Natural Science 6, no. 1 (August 3, 2023): 311–15. http://dx.doi.org/10.54254/2753-8818/6/20230265.
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G protein-coupled receptor can be written in GPCR, it has a big great family and this species include 800 human genes, it become the important part of human body. Although each species has their own unique skills, it can make different kind of medicine that can save humans life. And then there's the G-protein-coupled receptor mechanism. The GPCR desensitization regulator - arrestin was further analyzed, and researchers discovered that GPCRs could be activated not only through the G-protein-dependent pathway but also through the non-G-protein-dependent pathway, known as the -inhibitor pathway, to control the ingestion and desensitization throughout vivo and even start a new wave of signal transduction. The development of G-protein-coupled receptor drugs followed. GPCR is strongly associated to pathological conditions and has an essential function in cell signal transmission. More than 40% of the medicines on the market today target GPCR, which is the reached a high point family of pharmacological targets. The intracellular effector proteins (G proteins, etc.) that are activated by the GPCR play an important role in the regulation of its physiological function.
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Cheng, Han, Calli M. Lear-Rooney, Lisa Johansen, Elizabeth Varhegyi, Zheng W. Chen, Gene G. Olinger, and Lijun Rong. "Inhibition of Ebola and Marburg Virus Entry by G Protein-Coupled Receptor Antagonists." Journal of Virology 89, no. 19 (July 22, 2015): 9932–38. http://dx.doi.org/10.1128/jvi.01337-15.
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ABSTRACTFiloviruses, consisting of Ebola virus (EBOV) and Marburg virus (MARV), are among the most lethal infectious threats to mankind. Infections by these viruses can cause severe hemorrhagic fevers in humans and nonhuman primates with high mortality rates. Since there is currently no vaccine or antiviral therapy approved for humans, there is an urgent need to develop prophylactic and therapeutic options for use during filoviral outbreaks and bioterrorist attacks. One of the ideal targets against filoviral infection and diseases is at the entry step, which is mediated by the filoviral glycoprotein (GP). In this report, we screened a chemical library of small molecules and identified numerous inhibitors, which are known G protein-coupled receptor (GPCR) antagonists targeting different GPCRs, including histamine receptors, 5-HT (serotonin) receptors, muscarinic acetylcholine receptor, and adrenergic receptor. These inhibitors can effectively block replication of both infectious EBOV and MARV, indicating a broad antiviral activity of the GPCR antagonists. The time-of-addition experiment and microscopic studies suggest that GPCR antagonists block filoviral entry at a step following the initial attachment but prior to viral/cell membrane fusion. These results strongly suggest that GPCRs play a critical role in filoviral entry and GPCR antagonists can be developed as an effective anti-EBOV/MARV therapy.IMPORTANCEInfection of Ebola virus and Marburg virus can cause severe illness in humans with a high mortality rate, and currently there is no FDA-approved vaccine or therapeutic treatment available. The 2013-2015 epidemic in West Africa underscores a lack of our understanding in the infection and pathogenesis of these viruses and the urgency of drug discovery and development. In this study, we have identified numerous inhibitors that are known G protein-coupled receptor (GPCR) antagonists targeting different GPCRs. These inhibitors can effectively block replication of both infectious EBOV and MARV, indicating a broad antiviral activity of the GPCR antagonists. Our results strongly suggest that GPCRs play a critical role in filoviral entry and GPCR antagonists can be developed as an effective anti-EBOV/MARV therapy.
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Franco, Nuria, and Rafael Franco. "Understanding the Added Value of G-Protein-Coupled Receptor Heteromers." Scientifica 2014 (2014): 1–7. http://dx.doi.org/10.1155/2014/362937.
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G-protein-coupled receptors (GPCRs) constitute the most populated family of proteins within the human genome. Since the early sixties work on GPCRs and on GPCR-mediated signaling has led to a number of awards, the most recent being the Nobel Prize in Chemistry for 2012. The future of GPCRs research is surely based on their capacity for heteromerization. Receptor heteromers offer a series of challenges that will help in providing success in academic/basic research and translation into more effective and safer drugs.
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Bowman, Shanna Lynn, Daniel John Shiwarski, and Manojkumar A. Puthenveedu. "Distinct G protein–coupled receptor recycling pathways allow spatial control of downstream G protein signaling." Journal of Cell Biology 214, no. 7 (September 19, 2016): 797–806. http://dx.doi.org/10.1083/jcb.201512068.
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G protein–coupled receptors (GPCRs) are recycled via a sequence-dependent pathway that is spatially and biochemically distinct from bulk recycling. Why there are two distinct recycling pathways from the endosome is a fundamental question in cell biology. In this study, we show that the separation of these two pathways is essential for normal spatial encoding of GPCR signaling. The prototypical β-2 adrenergic receptor (B2AR) activates Gα stimulatory protein (Gαs) on the endosome exclusively in sequence-dependent recycling tubules marked by actin/sorting nexin/retromer tubular (ASRT) microdomains. B2AR was detected in an active conformation in bulk recycling tubules, but was unable to activate Gαs. Protein kinase A phosphorylation of B2AR increases the fraction of receptors localized to ASRT domains and biases the downstream transcriptional effects of B2AR to genes controlled by endosomal signals. Our results identify the physiological relevance of separating GPCR recycling from bulk recycling and suggest a mechanism to tune downstream responses of GPCR signaling by manipulating the spatial origin of G protein signaling.
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Ilyaskina, Olga S., Horst Lemoine, and Moritz Bünemann. "Lifetime of muscarinic receptor–G-protein complexes determines coupling efficiency and G-protein subtype selectivity." Proceedings of the National Academy of Sciences 115, no. 19 (April 23, 2018): 5016–21. http://dx.doi.org/10.1073/pnas.1715751115.
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G-protein–coupled receptors (GPCRs) are essential for the detection of extracellular stimuli by cells and transfer the encoded information via the activation of functionally distinct subsets of heterotrimeric G proteins into intracellular signals. Despite enormous achievements toward understanding GPCR structures, major aspects of the GPCR–G-protein selectivity mechanism remain unresolved. As this can be attributed to the lack of suitable and broadly applicable assays, we set out to develop a quantitative FRET-based assay to study kinetics and affinities of G protein binding to activated GPCRs in membranes of permeabilized cells in the absence of nucleotides. We measured the association and dissociation kinetics of agonist-induced binding of Gi/o, Gq/11, Gs, and G12/13 proteins to muscarinic M1, M2, and M3 receptors in the absence of nucleotides between fluorescently labeled G proteins and receptors expressed in mammalian cells. Our results show a strong quantitative correlation between not the on-rates of G-protein–M3–R interactions but rather the affinities of Gq and Go proteins to M3–Rs, their GPCR–G-protein lifetime and their coupling efficiencies determined in intact cells, suggesting that the G-protein subtype-specific affinity to the activated receptor in the absence of nucleotides is, in fact, a major determinant of the coupling efficiency. Our broadly applicable FRET-based assay represents a fast and reliable method to quantify the intrinsic affinity and relative coupling selectivity of GPCRs toward all G-protein subtypes.
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PFLEGER, Kevin D. G., and Karin A. EIDNE. "Monitoring the formation of dynamic G-protein-coupled receptor–protein complexes in living cells." Biochemical Journal 385, no. 3 (January 24, 2005): 625–37. http://dx.doi.org/10.1042/bj20041361.
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GPCRs (G-protein-coupled receptors) play an extremely important role in transducing extracellular signals across the cell membrane with high specificity and sensitivity. They are central to many of the body's endocrine and neurotransmitter pathways, and are consequently a major drug target. It is now clear that GPCRs interact with a range of proteins, including other GPCRs. Identifying and elucidating the function of such interactions will significantly enhance our understanding of cellular function, with the promise of new and improved pharmaceuticals. Biophysical techniques involving resonance energy transfer, namely FRET (fluorescence resonance energy transfer) and BRET (bioluminescence resonance energy transfer), now enable us to monitor the formation of dynamic GPCR–protein complexes in living cells, in real time. Their use has firmly established the concept of GPCR oligomerization, as well as demonstrating GPCR interactions with GPCR kinases, β-arrestins, adenylate cyclase and a subunit of an inwardly rectifying K+ channel. The present review examines recent technological advances and experimental applications of FRET and BRET, discussing particularly how they have been adapted to extract an ever-increasing amount of information about the nature, specificity, stoichiometry, kinetics and agonist-dependency of GPCR–protein interactions.
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Sato. "Conserved 2nd Residue of Helix 8 of GPCR May Confer the Subclass-Characteristic and Distinct Roles through a Rapid Initial Interaction with Specific G Proteins." International Journal of Molecular Sciences 20, no. 7 (April 9, 2019): 1752. http://dx.doi.org/10.3390/ijms20071752.
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To obtain a systematic view of the helix-8-second residue responsible for G protein-coupled receptor (GPCR)–G protein initial specific interactions, 786 human GPCRs were subclassified based on the pairs of agonist groups and target G proteins and compared with their conserved second residue of helix 8. Of 314 non-olfactory and deorphanized GPCRs, 273 (87%) conserved single amino acids in the subclasses, while 93 (58%) of the 160 subclasses possessed only a single GPCR member. Class B, C, Frizzled, and trace amine-associated GPCRs demonstrated 100% conservation, whereas class Ⅰ and Ⅱ olfactory and vomeronasal 1 receptors demonstrated much lower rates of conservation (20–47%). These conserved residues are characteristic of GPCR classes and G protein subtypes and confer their functionally-distinct roles.
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Croft, Wayne, Claire Hill, Eilish McCann, Michael Bond, Manuel Esparza-Franco, Jeannette Bennett, David Rand, John Davey, and Graham Ladds. "A Physiologically Required G Protein-coupled Receptor (GPCR)-Regulator of G Protein Signaling (RGS) Interaction That Compartmentalizes RGS Activity." Journal of Biological Chemistry 288, no. 38 (July 30, 2013): 27327–42. http://dx.doi.org/10.1074/jbc.m113.497826.
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G protein-coupled receptors (GPCRs) can interact with regulator of G protein signaling (RGS) proteins. However, the effects of such interactions on signal transduction and their physiological relevance have been largely undetermined. Ligand-bound GPCRs initiate by promoting exchange of GDP for GTP on the Gα subunit of heterotrimeric G proteins. Signaling is terminated by hydrolysis of GTP to GDP through intrinsic GTPase activity of the Gα subunit, a reaction catalyzed by RGS proteins. Using yeast as a tool to study GPCR signaling in isolation, we define an interaction between the cognate GPCR (Mam2) and RGS (Rgs1), mapping the interaction domains. This reaction tethers Rgs1 at the plasma membrane and is essential for physiological signaling response. In vivo quantitative data inform the development of a kinetic model of the GTPase cycle, which extends previous attempts by including GPCR-RGS interactions. In vivo and in silico data confirm that GPCR-RGS interactions can impose an additional layer of regulation through mediating RGS subcellular localization to compartmentalize RGS activity within a cell, thus highlighting their importance as potential targets to modulate GPCR signaling pathways.
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Ye, Ping, Barbara Mariniello, Franco Mantero, Hirotaka Shibata, and William E. Rainey. "G-protein-coupled receptors in aldosterone-producing adenomas: a potential cause of hyperaldosteronism." Journal of Endocrinology 195, no. 1 (October 2007): 39–48. http://dx.doi.org/10.1677/joe-07-0037.
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The source of aldosterone in 30–40% of patients with primary hyperaldosteronism (PA) is unilateral aldosterone-producing adenoma (APA). The mechanisms causing elevated aldosterone production in APA are unknown. Herein, we examined the expression of G-protein-coupled receptors (GPCRs) in APA and demonstrated that when compared with normal adrenals, there is a general elevation of certain GPCR in many APA and/or ectopic expression of GPCR in others. RNA samples from normal adrenals (n = 5), APAs (n = 10), and cortisol-producing adenomas (CPAs; n = 13) were used on 15 genomic expression arrays, each of which included 223 GPCR transcripts presented in at least 1 out of 15 of the independent microarrays. The array results were confirmed using real-time RT-PCR (qPCR). Four GPCR transcripts exhibited a statistically significant increase that was greater than threefold when compared with normal adrenals, suggesting a general increase in expression when compared with normal adrenal glands. Four GPCR transcripts exhibited a > 15-fold increase of expression in one or more of the APA samples when compared with normal adrenals. qPCR analysis confirmed array data and found the receptors with the highest fold increase in APA expression to be LH receptor, serotonin receptor 4, GnRH receptor, glutamate receptor metabotropic 3, endothelin receptor type B-like protein, and ACTH receptor. There are also sporadic increased expressions of these genes in the CPAs. Together, these findings suggest a potential role of altered GPCR expression in many cases of PA and provide candidate GPCR for further study.
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Lazim, Raudah, Donghyuk Suh, Jai Woo Lee, Thi Ngoc Lan Vu, Sanghee Yoon, and Sun Choi. "Structural Characterization of Receptor–Receptor Interactions in the Allosteric Modulation of G Protein-Coupled Receptor (GPCR) Dimers." International Journal of Molecular Sciences 22, no. 6 (March 22, 2021): 3241. http://dx.doi.org/10.3390/ijms22063241.
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G protein-coupled receptor (GPCR) oligomerization, while contentious, continues to attract the attention of researchers. Numerous experimental investigations have validated the presence of GPCR dimers, and the relevance of dimerization in the effectuation of physiological functions intensifies the attractiveness of this concept as a potential therapeutic target. GPCRs, as a single entity, have been the main source of scrutiny for drug design objectives for multiple diseases such as cancer, inflammation, cardiac, and respiratory diseases. The existence of dimers broadens the research scope of GPCR functions, revealing new signaling pathways that can be targeted for disease pathogenesis that have not previously been reported when GPCRs were only viewed in their monomeric form. This review will highlight several aspects of GPCR dimerization, which include a summary of the structural elucidation of the allosteric modulation of class C GPCR activation offered through recent solutions to the three-dimensional, full-length structures of metabotropic glutamate receptor and γ-aminobutyric acid B receptor as well as the role of dimerization in the modification of GPCR function and allostery. With the growing influence of computational methods in the study of GPCRs, we will also be reviewing recent computational tools that have been utilized to map protein–protein interactions (PPI).
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Osmond, Ronald I. W., Antony Sheehan, Romana Borowicz, Emma Barnett, Georgina Harvey, Cheryl Turner, Andrea Brown, Michael F. Crouch, and Anthony R. Dyer. "GPCR Screening via ERK 1/2: A Novel Platform for Screening G Protein–Coupled Receptors." Journal of Biomolecular Screening 10, no. 7 (September 16, 2005): 730–37. http://dx.doi.org/10.1177/1087057105277968.
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Discovery of novel agonists and antagonists for G protein–coupled receptors (GPCRs) relies heavily on cell-based assays because determination of functional consequences of receptor engagement is often desirable. Currently, there are several key parameters measured to achieve this, including mobilization of intracellular Ca2+ and formation of cyclic adenosine monophosphate or inositol triphosphate. However, no single assay platform is suitable for all situations, and all of the assays have limitations. The authors have developed a new high-throughput homogeneous assay platform for GPCR discovery as an alternative to current assays, which employs detection of phosphorylation of the key signaling molecule p42/44 MAP kinase (ERK 1/2). The authors show that ERK 1/2 is consistently activated in cells stimulated by Gq-coupled GPCRs and provides a new high-throughput platform for screening GPCR drug candidates. The activation of ERK 1/2 in Gq-coupled GPCR systems generates comparable pharmacological data for receptor agonist and antagonist data obtained by other GPCR activation measurement techniques.
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Walther, Cornelia, and Stephen S. G. Ferguson. "Minireview: Role of Intracellular Scaffolding Proteins in the Regulation of Endocrine G Protein-Coupled Receptor Signaling." Molecular Endocrinology 29, no. 6 (June 1, 2015): 814–30. http://dx.doi.org/10.1210/me.2015-1091.
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Abstract The majority of hormones stimulates and mediates their signal transduction via G protein-coupled receptors (GPCRs). The signal is transmitted into the cell due to the association of the GPCRs with heterotrimeric G proteins, which in turn activates an extensive array of signaling pathways to regulate cell physiology. However, GPCRs also function as scaffolds for the recruitment of a variety of cytoplasmic protein-interacting proteins that bind to both the intracellular face and protein interaction motifs encoded by GPCRs. The structural scaffolding of these proteins allows GPCRs to recruit large functional complexes that serve to modulate both G protein-dependent and -independent cellular signaling pathways and modulate GPCR intracellular trafficking. This review focuses on GPCR interacting PSD95-disc large-zona occludens domain containing scaffolds in the regulation of endocrine receptor signaling as well as their potential role as therapeutic targets for the treatment of endocrinopathies.
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Barwell, James, Mark Wheatley, Alex C. Conner, Bruck Taddese, Shabana Vohra, Christopher A. Reynolds, and David R. Poyner. "The activation of the CGRP receptor." Biochemical Society Transactions 41, no. 1 (January 29, 2013): 180–84. http://dx.doi.org/10.1042/bst20120251.
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The CGRP (calcitonin gene-related peptide) receptor is a family B GPCR (G-protein-coupled receptor). It consists of a GPCR, CLR (calcitonin receptor-like receptor) and an accessory protein, RAMP1 (receptor activity modifying protein 1). RAMP1 is needed for CGRP binding and also cell-surface expression of CLR. CLR is an example of a family B GPCR. Unlike family A GPCRs, little is known about how these receptors are activated by their endogenous ligands. This review considers what is known about the activation of family B GPCRs and then considers how this might be applied to CLR, particularly in light of new knowledge of the crystal structures of family A GPCRs.
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Conway, Bruce R., Lisa K. Minor, Jun Z. Xu, Joseph W. Gunnet, Robbin DeBiasio, Michael R. D'Andrea, Richard Rubin, et al. "Quantification of G-Protein Coupled Receptor Internalization Using G-Protein Coupled Receptor-Green Fluorescent Protein Conjugates with the ArrayScan™ High-Content Screening System." Journal of Biomolecular Screening 4, no. 2 (April 1999): 75–86. http://dx.doi.org/10.1177/108705719900400207.
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Many G-protein coupled receptors (GPCRs) undergo ligand-dependent homologous desensitization and internalization. Desensitization, defined as a decrease in the responsiveness to ligand, is accompanied by receptor aggregation on the cell surface and internalization via clathrin-coated pits to an intracellular endosomal compartment. In this study, we have taken advantage of the trafficking properties of GPCRs to develop a useful screening method for the identification of receptor mimetics. A series of studies were undertaken to evaluate the expression, functionality, and ligand-dependent trafficking of GPCR-green fluorescent protein (GFP) fusion conjugates stably transfected into HEK 293 cells. These GPCR-GFP expressing cells were then utilized in the validation of the ArrayScan™ (Cellomics™, Pittsburgh, PA), a microtiter plate imaging system that permits cellular and subcellular quantitation of fluorescence in whole cells. These studies demonstrated our ability to measure the internalization of a parathy-roid hormone (PTH) receptor-GFP conjugate after ligand treatment by spatially resolving internalized receptors. Internalization was time- and dose-dependent and appeared to be selective for PTH. Similar results were obtained for a β2-adrenergic receptor (β2 AR)-GFP conjugate stably expressed in HEK 293 cells. The internalized GFP-labeled receptors were visualized as numerous punctate "spots" within the cell interior. An algorithm has been developed that identifies and collects information about these spots, allowing quantification of the internalization process. Variables such as the receptor-GFP expression level, plating density, cell number per field, number of fields scanned per well, spot size, and spot intensity were evaluated during the development of this assay. The method represents a valuable tool to screen for receptor mimetics and antagonists of receptor internalization in whole cells rapidly.
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Miao, Yinglong, and J. Andrew McCammon. "Mechanism of the G-protein mimetic nanobody binding to a muscarinic G-protein-coupled receptor." Proceedings of the National Academy of Sciences 115, no. 12 (March 5, 2018): 3036–41. http://dx.doi.org/10.1073/pnas.1800756115.
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Protein–protein binding is key in cellular signaling processes. Molecular dynamics (MD) simulations of protein–protein binding, however, are challenging due to limited timescales. In particular, binding of the medically important G-protein-coupled receptors (GPCRs) with intracellular signaling proteins has not been simulated with MD to date. Here, we report a successful simulation of the binding of a G-protein mimetic nanobody to the M2 muscarinic GPCR using the robust Gaussian accelerated MD (GaMD) method. Through long-timescale GaMD simulations over 4,500 ns, the nanobody was observed to bind the receptor intracellular G-protein-coupling site, with a minimum rmsd of 2.48 Å in the nanobody core domain compared with the X-ray structure. Binding of the nanobody allosterically closed the orthosteric ligand-binding pocket, being consistent with the recent experimental finding. In the absence of nanobody binding, the receptor orthosteric pocket sampled open and fully open conformations. The GaMD simulations revealed two low-energy intermediate states during nanobody binding to the M2 receptor. The flexible receptor intracellular loops contribute remarkable electrostatic, polar, and hydrophobic residue interactions in recognition and binding of the nanobody. These simulations provided important insights into the mechanism of GPCR–nanobody binding and demonstrated the applicability of GaMD in modeling dynamic protein–protein interactions.
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Yadav, Dinesh Kumar, and Narendra Tuteja. "Rice G-protein coupled receptor (GPCR)." Plant Signaling & Behavior 6, no. 8 (August 2011): 1079–86. http://dx.doi.org/10.4161/psb.6.8.15771.
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García-Nafría, Javier, and Christopher G. Tate. "Cryo-Electron Microscopy: Moving Beyond X-Ray Crystal Structures for Drug Receptors and Drug Development." Annual Review of Pharmacology and Toxicology 60, no. 1 (January 6, 2020): 51–71. http://dx.doi.org/10.1146/annurev-pharmtox-010919-023545.
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Electron cryo-microscopy (cryo-EM) has revolutionized structure determination of membrane proteins and holds great potential for structure-based drug discovery. Here we discuss the potential of cryo-EM in the rational design of therapeutics for membrane proteins compared to X-ray crystallography. We also detail recent progress in the field of drug receptors, focusing on cryo-EM of two protein families with established therapeutic value, the γ-aminobutyric acid A receptors (GABAARs) and G protein–coupled receptors (GPCRs). GABAARs are pentameric ion channels, and cryo-EM structures of physiological heteromeric receptors in a lipid environment have uncovered the molecular basis of receptor modulation by drugs such as diazepam. The structures of ten GPCR–G protein complexes from three different classes of GPCRs have now been determined by cryo-EM. These structures give detailed insights into molecular interactions with drugs, GPCR–G protein selectivity, how accessory membrane proteins alter receptor–ligand pharmacology, and the mechanism by which HIV uses GPCRs to enter host cells.
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O'Dowd, Brian F., Mohammad Alijaniaram, Xiaodong Ji, Tuan Nguyen, Richard M. Eglen, and Susan R. George. "Using Ligand-Induced Conformational Change to Screen for Compounds Targeting G-Protein-Coupled Receptors." Journal of Biomolecular Screening 12, no. 2 (January 11, 2007): 175–85. http://dx.doi.org/10.1177/1087057106298287.
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The authors describe a novel drug strategy designed as a primary screen to discover either antagonist or agonist compounds targeting G-protein-coupled receptors (GPCRs). The incorporation of a nuclear localization sequence (NLS, a 5 amino acid substitution), in a location in helix 8 of the GPCR structure, resulted in ligand-independent receptor translocation from the cell surface to the nucleus. Blockade of the GPCR-NLS translocation from the cell surface was achieved by either antagonist or agonist treatments, each achieving their result in a sensitive concentration-dependent manner. GPCR-NLS translocation and blockade occurred regardless of the identity of the G-protein-coupling, and thus this assay is also ideally suited for identification of compounds targeting orphan GPCRs. The GPCR-NLS trafficking was visualized by fusion to fluorescent detectable proteins. Quantification of this effect was measured by determining the density of cell surface receptors, using enzyme fragment complementation in a manner suitable for high-throughput screening. Thus, the authors have developed a cellular assay for GPCRs suitable for compound screening without requiring prior identification of an agonist or knowledge of G-protein-coupling.
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Mary, Sophie, Jean-Alain Fehrentz, Marjorie Damian, Pascal Verdié, Jean Martinez, Jacky Marie, and Jean-Louis Banères. "How ligands and signalling proteins affect G-protein-coupled receptors' conformational landscape." Biochemical Society Transactions 41, no. 1 (January 29, 2013): 144–47. http://dx.doi.org/10.1042/bst20120267.
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The dynamic character of GPCRs (G-protein-coupled receptors) is essential to their function. However, the details of how ligands and signalling proteins stabilize a receptor conformation to trigger the activation of a given signalling pathway remain largely unexplored. Multiple data, including recent results obtained with the purified ghrelin receptor, suggest a model where ligand efficacy and functional selectivity are directly related to different receptor conformations. Importantly, distinct effector proteins (G-proteins and arrestins) as well as ligands are likely to affect the conformational landscape of GPCRs in different manners, as we show with the isolated ghrelin receptor. Such modulation of the GPCR conformational landscape by pharmacologically distinct ligands and effector proteins has major implications for the design of new drugs that activate specific signalling pathways.
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Sadee, Wolfgang. "Ligand-Free Signaling of G-Protein-Coupled Receptors: Physiology, Pharmacology, and Genetics." Molecules 28, no. 17 (August 31, 2023): 6375. http://dx.doi.org/10.3390/molecules28176375.
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G-protein-coupled receptors (GPCRs) are ubiquitous sensors and regulators of cellular functions. Each GPCR exists in complex aggregates with multiple resting and active conformations. Designed to detect weak stimuli, GPCRs can also activate spontaneously, resulting in basal ligand-free signaling. Agonists trigger a cascade of events leading to an activated agonist-receptor G-protein complex with high agonist affinity. However, the ensuing signaling process can further remodel the receptor complex to reduce agonist affinity, causing rapid ligand dissociation. The acutely activated ligand-free receptor can continue signaling, as proposed for rhodopsin and μ opioid receptors, resulting in robust receptor activation at low agonist occupancy with enhanced agonist potency. Continued receptor stimulation can further modify the receptor complex, regulating sustained ligand-free signaling—proposed to play a role in opioid dependence. Basal, acutely agonist-triggered, and sustained elevated ligand-free signaling could each have distinct functions, reflecting multi-state conformations of GPCRs. This review addresses basal and stimulus-activated ligand-free signaling, its regulation, genetic factors, and pharmacological implications, focusing on opioid and serotonin receptors, and the growth hormone secretagogue receptor (GHSR). The hypothesis is proposed that ligand-free signaling of 5-HT2A receptors mediate therapeutic effects of psychedelic drugs. Research avenues are suggested to close the gaps in our knowledge of ligand-free GPCR signaling.
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Wu, Na, Agnieszka M. Olechwier, Cyrill Brunner, Patricia C. Edwards, Ching-Ju Tsai, Christopher G. Tate, Gebhard F. X. Schertler, et al. "High-mass MALDI-MS unravels ligand-mediated G protein–coupling selectivity to GPCRs." Proceedings of the National Academy of Sciences 118, no. 31 (July 29, 2021): e2024146118. http://dx.doi.org/10.1073/pnas.2024146118.
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G protein–coupled receptors (GPCRs) are important pharmaceutical targets for the treatment of a broad spectrum of diseases. Although there are structures of GPCRs in their active conformation with bound ligands and G proteins, the detailed molecular interplay between the receptors and their signaling partners remains challenging to decipher. To address this, we developed a high-sensitivity, high-throughput matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) method to interrogate the first stage of signal transduction. GPCR–G protein complex formation is detected as a proxy for the effect of ligands on GPCR conformation and on coupling selectivity. Over 70 ligand–GPCR–partner protein combinations were studied using as little as 1.25 pmol protein per sample. We determined the selectivity profile and binding affinities of three GPCRs (rhodopsin, beta-1 adrenergic receptor [β1AR], and angiotensin II type 1 receptor) to engineered Gα-proteins (mGs, mGo, mGi, and mGq) and nanobody 80 (Nb80). We found that GPCRs in the absence of ligand can bind mGo, and that the role of the G protein C terminus in GPCR recognition is receptor-specific. We exemplified our quantification method using β1AR and demonstrated the allosteric effect of Nb80 binding in assisting displacement of nadolol to isoprenaline. We also quantified complex formation with wild-type heterotrimeric Gαiβγ and β-arrestin-1 and showed that carvedilol induces an increase in coupling of β-arrestin-1 and Gαiβγ to β1AR. A normalization strategy allows us to quantitatively measure the binding affinities of GPCRs to partner proteins. We anticipate that this methodology will find broad use in screening and characterization of GPCR-targeting drugs.
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Leifert, Wayne R., Amanda L. Aloia, Olgatina Bucco, Richard V. Glatz, and Edward J. McMurchie. "G-Protein-Coupled Receptors in Drug Discovery: Nanosizing Using Cell-Free Technologies and Molecular Biology Approaches." Journal of Biomolecular Screening 10, no. 8 (October 18, 2005): 765–79. http://dx.doi.org/10.1177/1087057105280517.
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Signal transduction by G-protein-coupled receptors (GPCRs) underpins a multitude of physiological processes. Ligand recognition by the receptor leads to activation of a genericmolecular switch involving heterotrimeric G-proteins and guanine nucleotides. Signal transduction has been studied extensively with both cell-based systems and assays comprising isolated signaling components. Interest and commercial investment in GPCRs in areas such as drug targets, orphan receptors, highthroughput screening, biosensors, and so on will focus greater attention on assay development to allow for miniaturization, ultra-high throughput and, eventually, microarray/biochip assay formats. Although cell-based assays are adequate for many GPCRs, it is likely that these formatswill limit the development of higher density GPCRassay platforms mandatory for other applications. Stable, robust, cell-free signaling assemblies comprising receptor and appropriate molecular switching components will form the basis of future GPCR assay platforms adaptable for such applications as microarrays. The authors review current cell-free GPCR assay technologies and molecular biological approaches for construction of novel, functional GPCR assays.
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Jeanneteau, Freddy, Olivier Guillin, Jorge Diaz, Nathalie Griffon, and Pierre Sokoloff. "GIPC Recruits GAIP (RGS19) To Attenuate Dopamine D2 Receptor Signaling." Molecular Biology of the Cell 15, no. 11 (November 2004): 4926–37. http://dx.doi.org/10.1091/mbc.e04-04-0285.
Full textAbstract:
Pleiotropic G proteins are essential for the action of hormones and neurotransmitters and are activated by stimulation of G protein–coupled receptors (GPCR), which initiates heterotrimer dissociation of the G protein, exchange of GDP for GTP on its Gα subunit and activation of effector proteins. Regulator of G protein signaling (RGS) proteins regulate this cascade and can be recruited to the membrane upon GPCR activation. Direct functional interaction between RGS and GPCR has been hypothesized. We show that recruitment of GAIP (RGS19) by the dopamine D2 receptor (D2R), a GPCR, required the scaffold protein GIPC (GAIP-interacting protein, C terminus) and that all three were coexpressed in neurons and neuroendocrine cells. Dynamic translocation of GAIP to the plasma membrane and coassembly in a protein complex in which GIPC was a required component was dictated by D2R activation and physical interactions. In addition, two different D2R-mediated responses were regulated by the GTPase activity of GAIP at the level of the G protein coupling in a GIPC-dependent manner. Since GIPC exclusively interacted with GAIP and selectively with subsets of GPCR, this mechanism may serve to sort GPCR signaling in cells that usually express a large repertoire of GPCRs, G proteins, and RGS.
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Calebiro, Davide, and Jak Grimes. "G Protein–Coupled Receptor Pharmacology at the Single-Molecule Level." Annual Review of Pharmacology and Toxicology 60, no. 1 (January 6, 2020): 73–87. http://dx.doi.org/10.1146/annurev-pharmtox-010919-023348.
Full textAbstract:
G protein–coupled receptors (GPCRs) mediate the effects of numerous hormones and neurotransmitters and are major pharmacological targets. Classical studies with crude cell lysates or membrane preparations have identified the main biochemical steps involved in GPCR signaling. Moreover, recent studies on purified proteins have provided astounding details at the atomic level of the 3-D structures of receptors in multiple conformations, including in complex with G proteins and β-arrestins. However, several fundamental questions remain regarding the highly specific effects and rapid nature of GPCR signaling. Recent developments in single-molecule microscopy are providing important contributions to answering these questions. Overall, single-molecule studies have revealed unexpected levels of complexity, with receptors existing in different conformations and dynamically interacting among themselves, their signaling partners, and structural elements of the plasma membrane to produce highly localized signals in space and time. These findings may provide a new basis to develop innovative strategies to modulate GPCR function for pharmacological purposes.
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Dijkman, Patricia M., Juan C. Muñoz-García, Steven R. Lavington, Patricia Suemy Kumagai, Rosana I. dos Reis, Daniel Yin, Phillip J. Stansfeld, Antonio José Costa-Filho, and Anthony Watts. "Conformational dynamics of a G protein–coupled receptor helix 8 in lipid membranes." Science Advances 6, no. 33 (August 2020): eaav8207. http://dx.doi.org/10.1126/sciadv.aav8207.
Full textAbstract:
G protein–coupled receptors (GPCRs) are the largest and pharmaceutically most important class of membrane proteins encoded in the human genome, characterized by a seven-transmembrane helix architecture and a C-terminal amphipathic helix 8 (H8). In a minority of GPCR structures solved to date, H8 either is absent or adopts an unusual conformation. The controversial existence of H8 of the class A GPCR neurotensin receptor 1 (NTS1) has been examined here for the nonthermostabilized receptor in a functionally supporting membrane environment using electron paramagnetic resonance, molecular dynamics simulations, and circular dichroism. Lipid-protein interactions with phosphatidylserine and phosphatidylethanolamine lipids, in particular, stabilize the residues 374 to 390 of NTS1 into forming a helix. Furthermore, introduction of a helix-breaking proline residue in H8 elicited an increase in ß-arrestin–NTS1 interactions observed in pull-down assays, suggesting that the structure and/or dynamics of H8 might play an important role in GPCR signaling.
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Stauch, Benjamin, and Vadim Cherezov. "Serial Femtosecond Crystallography of G Protein–Coupled Receptors." Annual Review of Biophysics 47, no. 1 (May 20, 2018): 377–97. http://dx.doi.org/10.1146/annurev-biophys-070317-033239.
Full textAbstract:
G protein–coupled receptors (GPCRs) represent a large superfamily of membrane proteins that mediate cell signaling and regulate a variety of physiological processes in the human body. Structure-function studies of this superfamily were enabled a decade ago by multiple breakthroughs in technology that included receptor stabilization, crystallization in a membrane environment, and microcrystallography. The recent emergence of X-ray free-electron lasers (XFELs) has further accelerated structural studies of GPCRs and other challenging proteins by overcoming radiation damage and providing access to high-resolution structures and dynamics using micrometer-sized crystals. Here, we summarize key technology advancements and major milestones of GPCR research using XFELs and provide a brief outlook on future developments in the field.
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Rahman, Md Mominur, Md Rezaul Islam, Sadia Afsana Mim, Nasrin Sultana, Dinesh Kumar Chellappan, Kamal Dua, Mohammad Amjad Kamal, Rohit Sharma, and Talha Bin Emran. "Insights into the Promising Prospect of G Protein and GPCR-Mediated Signaling in Neuropathophysiology and Its Therapeutic Regulation." Oxidative Medicine and Cellular Longevity 2022 (September 21, 2022): 1–22. http://dx.doi.org/10.1155/2022/8425640.
Full textAbstract:
G protein-coupled receptors (GPCRs) are intricately involved in the conversion of extracellular feedback to intracellular responses. These specialized receptors possess a crucial role in neurological and psychiatric disorders. Most nonsensory GPCRs are active in almost 90% of complex brain functions. At the time of receptor phosphorylation, a GPCR pathway is essentially activated through a G protein signaling mechanism via a G protein-coupled receptor kinase (GRK). Dopamine, an important neurotransmitter, is primarily involved in the pathophysiology of several CNS disorders; for instance, bipolar disorder, schizophrenia, Parkinson’s disease, and ADHD. Since dopamine, acetylcholine, and glutamate are potent neuropharmacological targets, dopamine itself has potential therapeutic effects in several CNS disorders. GPCRs essentially regulate brain functions by modulating downstream signaling pathways. GPR6, GPR52, and GPR8 are termed orphan GPCRs because they colocalize with dopamine D1 and D2 receptors in neurons of the basal ganglia, either alone or with both receptors. Among the orphan GPCRs, the GPR52 is recognized for being an effective psychiatric receptor. Various antipsychotics like aripiprazole and quetiapine mainly target GPCRs to exert their actions. One of the most important parts of signal transduction is the regulation of G protein signaling (RGS). These substances inhibit the activation of the G protein that initiates GPCR signaling. Developing a combination of RGS inhibitors with GPCR agonists may prove to have promising therapeutic potential. Indeed, several recent studies have suggested that GPCRs represent potentially valuable therapeutic targets for various psychiatric disorders. Molecular biology and genetically modified animal model studies recommend that these enriched GPCRs may also act as potential therapeutic psychoreceptors. Neurotransmitter and neuropeptide GPCR malfunction in the frontal cortex and limbic-related regions, including the hippocampus, hypothalamus, and brainstem, is likely responsible for the complex clinical picture that includes cognitive, perceptual, emotional, and motor symptoms. G protein and GPCR-mediated signaling play a critical role in developing new treatment options for mental health issues, and this study is aimed at offering a thorough picture of that involvement. For patients who are resistant to current therapies, the development of new drugs that target GPCR signaling cascades remains an interesting possibility. These discoveries might serve as a fresh foundation for the creation of creative methods for pharmacologically useful modulation of GPCR function.
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Jiang, Yuhong, Xin Zhuo, and Canquan Mao. "G Protein-coupled Receptors in Cancer Stem Cells." Current Pharmaceutical Design 26, no. 17 (June 7, 2020): 1952–63. http://dx.doi.org/10.2174/1381612826666200305130009.
Full textAbstract:
G protein-coupled receptors (GPCRs) are highly expressed on a variety of tumour tissues while several GPCR exogenous ligands become marketed pharmaceuticals. In recent decades, cancer stem cells (CSCs) become widely investigated drug targets for cancer therapy but the underlying mechanism is still not fully elucidated. There are vigorous participations of GPCRs in CSCs-related signalling and functions, such as biomarkers for CSCs, activation of Wnt, Hedgehog (HH) and other signalling to facilitate CSCs progressions. This relationship can not only uncover a novel molecular mechanism for GPCR-mediated cancer cell functions but also assist our understanding of maintaining and modulating CSCs. Moreover, GPCR antagonists and monoclonal antibodies could be applied to impair CSCs functions and consequently attenuate tumour growth, some of which have been undergoing clinical studies and are anticipated to turn into marketed anticancer drugs. Therefore, this review summarizes and provides sufficient evidences on the regulation of GPCR signalling in the maintenance, differentiation and pluripotency of CSCs, suggesting that targeting GPCRs on the surface of CSCs could be potential therapeutic strategies for cancer therapy.