The idea of receptors has fascinated scientists for more than a century. Today it is known that the G‐protein coupled receptors (GPCRs) represent by far the largest, most versatile and most ...ubiquitous of the several families of plasma membrane receptors. The Nobel Prize for Chemistry 2012 was awarded for studies on GPCRs.
G protein-coupled receptors (GPCRs) are privileged structural scaffolds in biology that have the versatility to regulate diverse physiological processes. Interestingly, many GPCR ligands exhibit ...significant ‘bias’ – the ability to preferentially activate subsets of the many cellular pathways downstream of these receptors. Recently, complementary information from structural and spectroscopic approaches has made significant inroads into understanding the mechanisms of these biased ligands. The consistently emerging theme is that GPCRs are highly dynamic proteins, and ligands with varying pharmacological properties differentially modulate the equilibrium among multiple conformations. Biased signaling and other recently appreciated complexities of GPCR signaling thus appear to be a natural consequence of the conformational heterogeneity of GPCRs and GPCR–transducer complexes.
G protein-coupled receptors (GPCRs) activate multiple pathways in the cell, and certain ‘biased’ GPCR ligands are able to preferentially stimulate particular pathways.A full picture of how different ligands produce different signaling patterns requires data from multiple biophysical techniques providing high-resolution structural details and dynamic information on GPCR conformations.GPCRs sample more than just a single ‘inactive’ and a single ‘active’ conformation, and the endogenous agonists of most receptors stabilize a mixture of multiple conformations.Biased ligands can achieve their distinctive signaling profiles by modulating this distribution of receptor conformations.This conformational heterogeneity is likely to be a major reason why GPCRs are privileged structural scaffolds in biology and provides a biophysical basis for their versatility.
G protein-coupled receptors (GPCRs) are the largest class of receptors in the human genome and some of the most common drug targets. It is now well established that GPCRs can signal through multiple ...transducers, including heterotrimeric G proteins, GPCR kinases and β-arrestins. While these signalling pathways can be activated or blocked by 'balanced' agonists or antagonists, they can also be selectively activated in a 'biased' response. Biased responses can be induced by biased ligands, biased receptors or system bias, any of which can result in preferential signalling through G proteins or β-arrestins. At many GPCRs, signalling events mediated by G proteins and β-arrestins have been shown to have distinct biochemical and physiological actions from one another, and an accurate evaluation of biased signalling from pharmacology through physiology is crucial for preclinical drug development. Recent structural studies have provided snapshots of GPCR-transducer complexes, which should aid in the structure-based design of novel biased therapies. Our understanding of GPCRs has evolved from that of two-state, on-and-off switches to that of multistate allosteric microprocessors, in which biased ligands transmit distinct structural information that is processed into distinct biological outputs. The development of biased ligands as therapeutics heralds an era of increased drug efficacy with reduced drug side effects.
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.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The concept of biased agonism has recently come to the fore with the realization that seven-transmembrane receptors (7TMRs, also known as G protein-coupled receptors, or GPCRs) activate complex ...signaling networks and can adopt multiple active conformations upon agonist binding. As a consequence, the "efficacy" of receptors, which was classically considered linear, is now recognized as pluridimensional. Biased agonists selectively stabilize only a subset of receptor conformations induced by the natural "unbiased" ligand, thus preferentially activating certain signaling mechanisms. Such agonists thus reveal the intriguing possibility that one can direct cellular signaling with unprecedented precision and specificity and support the notion that biased agonists may identify new classes of therapeutic agents that have fewer side effects. This review focuses on one particular class of biased ligands that has the ability to alter the balance between G protein-dependent and β-arrestin-dependent signal transduction.
Stimulation of cell-surface seven-transmembrane receptors (7TMRs) elicits biological responses to a wide range of extracellular signals, including many hormones. Classically, heterotrimeric ...GTP-binding proteins (G proteins) are recruited to the activated conformation of 7TMRs. Only two other families of protein have this remarkable characteristic: G-protein-coupled receptor kinases and β-arrestins. These two protein families have long been known to have a central and coordinated role in the ‘desensitization’ of G protein activation by 7TMRs. In addition, G-protein-coupled receptor kinases and β-arrestins are involved in an increasing number of interactions with non-receptor proteins, broadening the variety of their cellular functions. These newly appreciated attributes of these two families of protein highlight their unique ability to coordinate the various aspects of 7TMR functions.
The angiotensin II (AngII) type 1 receptor (AT1R) is a critical regulator of cardiovascular and renal function and is an important model for studies of G-protein-coupled receptor (GPCR) signaling. By ...stabilizing the receptor with a single-domain antibody fragment (“nanobody”) discovered using a synthetic yeast-displayed library, we determined the crystal structure of active-state human AT1R bound to an AngII analog with partial agonist activity. The nanobody binds to the receptor’s intracellular transducer pocket, stabilizing the large conformational changes characteristic of activated GPCRs. The peptide engages the AT1R through an extensive interface spanning from the receptor core to its extracellular face and N terminus, remodeling the ligand-binding cavity. Remarkably, the mechanism used to propagate conformational changes through the receptor diverges from other GPCRs at several key sites, highlighting the diversity of allosteric mechanisms among GPCRs. Our structure provides insight into how AngII and its analogs stimulate full or biased signaling, respectively.
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•Active angiotensin II type 1 receptor crystallized with angiotensin II peptide analog•Stabilized by a conformation-specific synthetic nanobody discovered by yeast display•Extensive peptide-receptor engagement remodels ligand-binding cavity•Intra- and extracellular changes give insights on GPCR activation and biased agonism
Structural analysis of the interactions between the angiotensin receptor and a partial agonist shows how peptide ligands induce receptor activation.
G protein-coupled receptors (GPCRs) regulate cellular signaling pathways by coupling to two classes of transducers: heterotrimeric G proteins and β-arrestins. Sarcosine1Ile4Ile8-angiotensin II (SII), ...an analog of the endogenous ligand angiotensin II (AngII) for the angiotensin II type 1 receptor (AT1R), fails to activate G protein in physiologically relevant models. Despite this, SII and several derivatives induce cellular signaling outcomes through β-arrestin-2-dependent mechanisms. However, studies reliant on exogenous AT1R overexpression indicate that SII is a partial agonist for G protein signaling and lacks β-arrestin-exclusive functional specificity. We investigated this apparent discrepancy by profiling changes in functional specificity at increasing expression levels of AT1R using a stably integrated tetracycline-titratable expression system stimulated with AngII, SII, and four other AngII analogs displaying different signaling biases. Unbiased and G protein-biased ligands activated dose-dependent calcium responses at all tested receptor concentrations. In contrast, β-arrestin-biased ligands induced dose-dependent calcium signaling only at higher AT1R overexpression levels. Using inhibitors of G proteins, we demonstrated that both Gi and Gq/11 mediated overexpression-dependent calcium signaling by β-arrestin-biased ligands. Regarding β-arrestin-mediated cellular events, the β-arrestin-biased ligand TRV026 induced receptor internalization at low physiological receptor levels insufficient for it to initiate calcium signaling. In contrast, unbiased AngII exhibited no relative preference between these outcomes under such low receptor conditions. However, with high receptor overexpression, TRV026 lost its functional selectivity. These results suggest receptor overexpression misleadingly distorts the bias of AT1R ligands and highlight the risks of using overexpressed systems to infer the signaling bias of GPCR ligands in physiologically relevant contexts.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
β-Arrestins function as endocytic adaptors and mediate trafficking of a variety of cell-surface receptors, including seven-transmembrane receptors (7TMRs). In the case of 7TMRs, β-arrestins carry out ...these tasks while simultaneously inhibiting upstream G-protein-dependent signaling and promoting alternate downstream signaling pathways. The mechanisms by which β-arrestins interact with a continuously expanding ensemble of protein partners and perform their multiple functions including trafficking and signaling are currently being uncovered. Molecular changes at the level of protein conformation as well as post-translational modifications of β-arrestins probably form the basis for their dynamic interactions during receptor trafficking and signaling. It is becoming increasingly evident that β-arrestins, originally discovered as 7TMR adaptor proteins, indeed have much broader and more versatile roles in maintaining cellular homeostasis. In this review paper, we assess the traditional and novel functions of β-arrestins and discuss the molecular attributes that might facilitate multiple interactions in regulating cell signaling and receptor trafficking.
Members of the seven-transmembrane receptor (7TMR), or G protein-coupled receptor (GPCR), superfamily represent some of the most successful targets of modern drug therapy, with proven efficacy in the ...treatment of a broad range of human conditions and disease processes. It is now appreciated that β-arrestins, once viewed simply as negative regulators of traditional 7TMR-stimulated G protein signaling, act as multifunctional adapter proteins that regulate 7TMR desensitization and trafficking and promote distinct intracellular signals in their own right. Moreover, several 7TMR biased agonists, which selectively activate these divergent signaling pathways, have been identified. Here we highlight the diversity of G protein- and β-arrestin-mediated functions and the therapeutic potential of selective targeting of these in disease states.
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