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Molecular and Cellular Endocrinology Mar 2019G protein-coupled receptors (GPCRs) are the largest family of signaling proteins targeted by more clinically used drugs than any other protein family. GPCR signaling via... (Review)
Review
G protein-coupled receptors (GPCRs) are the largest family of signaling proteins targeted by more clinically used drugs than any other protein family. GPCR signaling via G proteins is quenched (desensitized) by the phosphorylation of the active receptor by specific GPCR kinases (GRKs) followed by tight binding of arrestins to active phosphorylated receptors. Thus, arrestins engage two types of receptor elements: those that contain GRK-added phosphates and those that change conformation upon activation. GRKs attach phosphates to serines and threonines in the GPCR C-terminus or any one of the cytoplasmic loops. In addition to these phosphates, arrestins engage the cavity that appears between trans-membrane helices upon receptor activation and several other non-phosphorylated elements. The residues that bind GPCRs are localized on the concave side of both arrestin domains. Arrestins undergo a global conformational change upon receptor binding (become activated). Arrestins serve as important hubs of cellular signaling, emanating from activated GPCRs and receptor-independent.
Topics: Animals; Arrestin; Binding Sites; G-Protein-Coupled Receptor Kinases; Humans; Models, Molecular; Phosphorylation; Protein Binding; Protein Conformation; Protein Domains; Receptors, G-Protein-Coupled
PubMed: 30703488
DOI: 10.1016/j.mce.2019.01.019 -
International Journal of Molecular... Nov 2017G protein-coupled receptors (GPCRs) are cell surface receptors that respond to a wide variety of stimuli, from light, odorants, hormones, and neurotransmitters to... (Review)
Review
G protein-coupled receptors (GPCRs) are cell surface receptors that respond to a wide variety of stimuli, from light, odorants, hormones, and neurotransmitters to proteins and extracellular calcium. GPCRs represent the largest family of signaling proteins targeted by many clinically used drugs. Recent studies shed light on the conformational changes that accompany GPCR activation and the structural state of the receptor necessary for the interactions with the three classes of proteins that preferentially bind active GPCRs, G proteins, G protein-coupled receptor kinases (GRKs), and arrestins. Importantly, structural and biophysical studies also revealed activation-related conformational changes in these three types of signal transducers. Here, we summarize what is already known and point out questions that still need to be answered. Clear understanding of the structural basis of signaling by GPCRs and their interaction partners would pave the way to designing signaling-biased proteins with scientific and therapeutic potential.
Topics: Animals; Arrestins; Humans; Protein Domains; Receptors, G-Protein-Coupled; Signal Transduction
PubMed: 29186792
DOI: 10.3390/ijms18122519 -
Progress in Molecular Biology and... 2019Arrestins play a key role in homologous desensitization of G protein-coupled receptors (GPCRs) and regulate several other vital signaling pathways in cells. Considering... (Review)
Review
Arrestins play a key role in homologous desensitization of G protein-coupled receptors (GPCRs) and regulate several other vital signaling pathways in cells. Considering the critical roles of these proteins in cellular signaling, surprisingly few disease-causing mutations in human arrestins were described. Most of these are loss-of-function mutations of visual arrestin-1 that cause excessive rhodopsin signaling and hence night blindness. Only one dominant arrestin-1 mutation was discovered so far. It reduces the thermal stability of the protein, which likely results in photoreceptor death via unfolded protein response. In case of the two nonvisual arrestins, only polymorphisms were described, some of which appear to be associated with neurological disorders and altered response to certain treatments. Structure-function studies revealed several ways of enhancing arrestins' ability to quench GPCR signaling. These enhanced arrestins have potential as tools for gene therapy of disorders associated with excessive signaling of mutant GPCRs.
Topics: Animals; Arrestin; Disease; Eye; Humans; Mammals; Models, Biological; Mutation
PubMed: 30711028
DOI: 10.1016/bs.pmbts.2018.09.004 -
Journal of Neurochemistry May 2021The finger loop in the central crest of the receptor-binding site of arrestins engages the cavity between the transmembrane helices of activated G-protein-coupled...
The finger loop in the central crest of the receptor-binding site of arrestins engages the cavity between the transmembrane helices of activated G-protein-coupled receptors. Therefore, it was hypothesized to serve as the sensor that detects the activation state of the receptor. We performed comprehensive mutagenesis of the finger loop in bovine visual arrestin-1, generated mutant radiolabeled proteins by cell-free translation, and determined the effects of mutations on the in vitro binding of arrestin-1 to purified phosphorylated light-activated rhodopsin. This interaction is driven by two factors, rhodopsin activation and rhodopsin-attached phosphates. Therefore, the binding of arrestin-1 to light-activated unphosphorylated rhodopsin is low. To evaluate the role of the finger loop specifically in the recognition of the active receptor conformation, we tested the effects of these mutations in the context of truncated arrestin-1 that demonstrates much higher binding to unphosphorylated activated and phosphorylated inactive rhodopsin. The majority of finger loop residues proved important for arrestin-1 binding to light-activated rhodopsin, with six mutations affecting the binding exclusively to this form. Thus, the finger loop is the key element of arrestin-1 activation sensor. The data also suggest that arrestin-1 and its enhanced mutant bind various functional forms of rhodopsin differently.
Topics: Animals; Arrestin; Binding Sites; Cattle; Protein Binding; Protein Structure, Secondary
PubMed: 33159335
DOI: 10.1111/jnc.15232 -
Nature Reviews. Drug Discovery May 2010Seven-transmembrane receptors (7TMRs; also known as G protein-coupled receptors) are the largest class of receptors in the human genome and are common targets for... (Review)
Review
Seven-transmembrane receptors (7TMRs; also known as G protein-coupled receptors) are the largest class of receptors in the human genome and are common targets for therapeutics. Originally identified as mediators of 7TMR desensitization, beta-arrestins (arrestin 2 and arrestin 3) are now recognized as true adaptor proteins that transduce signals to multiple effector pathways. Signalling that is mediated by beta-arrestins has distinct biochemical and functional consequences from those mediated by G proteins, and several biased ligands and receptors have been identified that preferentially signal through either G protein- or beta-arrestin-mediated pathways. These ligands are not only useful tools for investigating the biochemistry of 7TMR signalling, they also have the potential to be developed into new classes of therapeutics.
Topics: Animals; Arrestins; Drug Delivery Systems; Drug Design; Genome, Human; Humans; Ligands; Receptors, G-Protein-Coupled; Signal Transduction; beta-Arrestins
PubMed: 20431569
DOI: 10.1038/nrd3024 -
MBio Nov 2019Arrestins, a structurally specialized and functionally diverse group of proteins, are central regulators of adaptive cellular responses in eukaryotes. Previous studies...
Arrestins, a structurally specialized and functionally diverse group of proteins, are central regulators of adaptive cellular responses in eukaryotes. Previous studies on fungal arrestins have demonstrated their capacity to modulate diverse cellular processes through their adaptor functions, facilitating the localization and function of other proteins. However, the mechanisms by which arrestin-regulated processes are involved in fungal virulence remain unexplored. We have identified a small family of four arrestins, Ali1, Ali2, Ali3, and Ali4, in the human fungal pathogen Using complementary microscopy, proteomic, and reverse genetics techniques, we have defined a role for Ali1 as a novel contributor to cytokinesis, a fundamental cell cycle-associated process. We observed that Ali1 strongly interacts with proteins involved in lipid synthesis, and that Δ mutant phenotypes are rescued by supplementation with lipid precursors that are used to build cellular membranes. From these data, we hypothesize that Ali1 contributes to cytokinesis by serving as an adaptor protein, facilitating the localization of enzymes that modify the plasma membrane during cell division, specifically the fatty acid synthases Fas1 and Fas2. Finally, we assessed the contributions of the arrestin family to virulence to better understand the mechanisms by which arrestin-regulated adaptive cellular responses influence fungal infection. We observed that the arrestin family contributes to virulence, and that the individual arrestin proteins likely fulfill distinct functions that are important for disease progression. To survive under unpredictable conditions, all organisms must adapt to stressors by regulating adaptive cellular responses. Arrestin proteins are conserved regulators of adaptive cellular responses in eukaryotes. Studies that have been limited to mammals and model fungi have demonstrated that the disruption of arrestin-regulated pathways is detrimental for viability. The human fungal pathogen causes more than 180,000 infection-related deaths annually, especially among immunocompromised patients. In addition to being genetically tractable, has a small arrestin family of four members, lending itself to a comprehensive characterization of its arrestin family. This study serves as a functional analysis of arrestins in a pathogen, particularly in the context of fungal fitness and virulence. We investigate the functions of one arrestin protein, Ali1, and define its novel contributions to cytokinesis. We additionally explore the virulence contributions of the arrestin family and find that they contribute to disease establishment and progression.
Topics: Arrestin; Biomarkers; Cell Cycle; Cytokinesis; Disease Susceptibility; Fungal Proteins; Fungi; Lipid Metabolism; Models, Biological; Mutation; Mycoses; Virulence; ras Proteins
PubMed: 31744923
DOI: 10.1128/mBio.02682-19 -
British Journal of Pharmacology Aug 2022The interaction of arrestins with G-protein coupled receptors (GPCRs) desensitizes agonist-dependent receptor responses and often leads to receptor internalization....
BACKGROUND AND PURPOSE
The interaction of arrestins with G-protein coupled receptors (GPCRs) desensitizes agonist-dependent receptor responses and often leads to receptor internalization. GPCRs that internalize without arrestin have been classified as "class A" GPCRs whereas "class B" GPCRs co-internalize with arrestin into endosomes. The interaction of arrestins with GPCRs requires both agonist activation and receptor phosphorylation. Here, we ask the question whether agonists with very slow off-rates can cause the formation of particularly stable receptor-arrestin complexes.
EXPERIMENTAL APPROACH
The stability of GPCR-arrestin-3 complexes at two class A GPCRs, the β -adrenoceptor and the μ opioid receptor, was assessed using two different techniques, fluorescence resonance energy transfer (FRET) and fluorescence recovery after photobleaching (FRAP) employing several ligands with very different off-rates. Arrestin trafficking was determined by confocal microscopy.
KEY RESULTS
Upon agonist washout, GPCR-arrestin-3 complexes showed markedly different dissociation rates in single-cell FRET experiments. In FRAP experiments, however, all full agonists led to the formation of receptor-arrestin complexes of identical stability whereas the complex between the μ receptor and arrestin-3 induced by the partial agonist morphine was less stable. Agonists with very slow off-rates could not mediate the co-internalization of arrestin-3 with class A GPCRs into endosomes.
CONCLUSIONS AND IMPLICATIONS
Agonist off-rates do not affect the stability of GPCR-arrestin complexes but phosphorylation patterns do. Our results imply that orthosteric agonists are not able to pharmacologically convert class A into class B GPCRs.
Topics: Arrestin; Arrestins; Internship and Residency; Receptors, G-Protein-Coupled; beta-Arrestin 2; beta-Arrestins
PubMed: 35352338
DOI: 10.1111/bph.15846 -
Cell Dec 2020Binding of arrestin to phosphorylated G-protein-coupled receptors (GPCRs) controls many aspects of cell signaling. The number and arrangement of phosphates may vary...
Binding of arrestin to phosphorylated G-protein-coupled receptors (GPCRs) controls many aspects of cell signaling. The number and arrangement of phosphates may vary substantially for a given GPCR, and different phosphorylation patterns trigger different arrestin-mediated effects. Here, we determine how GPCR phosphorylation influences arrestin behavior by using atomic-level simulations and site-directed spectroscopy to reveal the effects of phosphorylation patterns on arrestin binding and conformation. We find that patterns favoring binding differ from those favoring activation-associated conformational change. Both binding and conformation depend more on arrangement of phosphates than on their total number, with phosphorylation at different positions sometimes exerting opposite effects. Phosphorylation patterns selectively favor a wide variety of arrestin conformations, differently affecting arrestin sites implicated in scaffolding distinct signaling proteins. We also reveal molecular mechanisms of these phenomena. Our work reveals the structural basis for the long-standing "barcode" hypothesis and has important implications for design of functionally selective GPCR-targeted drugs.
Topics: Arrestin; Computer Simulation; HEK293 Cells; Humans; Phosphates; Phosphopeptides; Phosphorylation; Protein Binding; Protein Conformation; Receptors, G-Protein-Coupled; Signal Transduction; Spectrum Analysis
PubMed: 33296703
DOI: 10.1016/j.cell.2020.11.014 -
Pharmacological Reviews Jun 2010Heptahelical G protein-coupled receptors are the most diverse and therapeutically important family of receptors in the human genome. Ligand binding activates... (Review)
Review
Heptahelical G protein-coupled receptors are the most diverse and therapeutically important family of receptors in the human genome. Ligand binding activates heterotrimeric G proteins that transmit intracellular signals by regulating effector enzymes or ion channels. G protein signaling is terminated, in large part, by arrestin binding, which uncouples the receptor and G protein and targets the receptor for internalization. It is clear, however, that heptahelical receptor signaling does not end with desensitization. Arrestins bind a host of catalytically active proteins and serve as ligand-regulated scaffolds that recruit protein and lipid kinase, phosphatase, phosphodiesterase, and ubiquitin ligase activity into the receptor-arrestin complex. Although many of these arrestin-bound effectors serve to modulate G protein signaling, degrading second messengers and regulating endocytosis and trafficking, other signals seem to extend beyond the receptor-arrestin complex to regulate such processes as protein translation and gene transcription. Although these findings have led to a re-envisioning of heptahelical receptor signaling, little is known about the physiological roles of arrestin-dependent signaling. In vivo, the duality of arrestin function makes it difficult to dissociate the consequences of arrestin-dependent desensitization from those that might be ascribed to arrestin-mediated signaling. Nonetheless, recent evidence generated using arrestin knockouts, G protein-uncoupled receptor mutants, and arrestin pathway-selective "biased agonists" is beginning to reveal that arrestin signaling plays important roles in the retina, central nervous system, cardiovascular system, bone remodeling, immune system, and cancer. Understanding the signaling roles of arrestins may foster the development of pathway-selective drugs that exploit these pathways for therapeutic benefit.
Topics: Arrestin; Endocytosis; GTP-Binding Protein Regulators; Heterotrimeric GTP-Binding Proteins; Humans; Receptors, G-Protein-Coupled; Signal Transduction
PubMed: 20427692
DOI: 10.1124/pr.109.002436 -
International Journal of Molecular... Nov 2021Arrestins are a small family of proteins that bind G protein-coupled receptors (GPCRs). Arrestin binds to active phosphorylated GPCRs with higher affinity than to all... (Review)
Review
Arrestins are a small family of proteins that bind G protein-coupled receptors (GPCRs). Arrestin binds to active phosphorylated GPCRs with higher affinity than to all other functional forms of the receptor, including inactive phosphorylated and active unphosphorylated. The selectivity of arrestins suggests that they must have two sensors, which detect receptor-attached phosphates and the active receptor conformation independently. Simultaneous engagement of both sensors enables arrestin transition into a high-affinity receptor-binding state. This transition involves a global conformational rearrangement that brings additional elements of the arrestin molecule, including the middle loop, in contact with a GPCR, thereby stabilizing the complex. Here, we review structural and mutagenesis data that identify these two sensors and additional receptor-binding elements within the arrestin molecule. While most data were obtained with the arrestin-1-rhodopsin pair, the evidence suggests that all arrestins use similar mechanisms to achieve preferential binding to active phosphorylated GPCRs.
Topics: Arrestin; Binding Sites; Humans; Mutagenesis; Phosphorylation; Protein Binding; Protein Conformation; Receptors, G-Protein-Coupled; Rhodopsin
PubMed: 34830362
DOI: 10.3390/ijms222212481