scholarly journals Correlated motions of conserved polar motifs lay out a plausible mechanism of G protein-coupled receptor activation.

2020 ◽  
Author(s):  
Argha Mitra ◽  
Arijit Sarkar ◽  
Marton Richard Szabo ◽  
Attila Borics
Keyword(s):  
G Protein ◽  
Intracellular Signaling ◽  
Transmembrane Helix ◽  
Receptor Activation ◽  
Current Theory ◽  
Activation Mechanism ◽  
Structural Basis ◽  
Binding Interface ◽  
Gpcr Activation ◽  
G Protein Coupled

Recent advancements in the field of experimental structural biology have provided high-resolution structures of active and inactive state G protein-coupled receptors (GPCRs), a highly important pharmaceutical target family, but the process of transition between these states is poorly understood. According to the current theory, GPCRs exist in structurally distinct, dynamically interconverting functional states of which populations are shifted upon binding of ligands and intracellular signaling proteins. However, explanation of the activation mechanism on an entirely structural basis gets complicated when multiple activation pathways and active receptor states are considered. Our unbiased, atomistic molecular dynamics simulations of the mu-opioid receptor in a physiological environment revealed that external stimulus is propagated to the intracellular surface of the receptor through subtle, concerted movements of highly conserved polar amino acid side chains along the 7th transmembrane helix. To amend the widely accepted theory we suggest that the initiation event of GPCR activation is the shift of macroscopic polarization between the ortho- and allosteric binding pockets and the intracellular G protein-binding interface.

scholarly journals Correlated Motions of Conserved Polar Motifs Lay out a Plausible Mechanism of G Protein-Coupled Receptor Activation

Biomolecules ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 670
Author(s):  
Argha Mitra ◽  
Arijit Sarkar ◽  
Márton Richárd Szabó ◽  
Attila Borics
Keyword(s):  
G Protein ◽  
Intracellular Signaling ◽  
Transmembrane Domain ◽  
Receptor Activation ◽  
Activation Mechanism ◽  
Structural Basis ◽  
Binding Interface ◽  
Gpcr Activation ◽  
Macroscopic Polarization ◽  
G Protein Coupled

Recent advancements in the field of experimental structural biology have provided high-resolution structures of active and inactive state G protein-coupled receptors (GPCRs), a highly important pharmaceutical target family, but the process of transition between these states is poorly understood. According to the current theory, GPCRs exist in structurally distinct, dynamically interconverting functional states of which populations are shifted upon binding of ligands and intracellular signaling proteins. However, explanation of the activation mechanism, on an entirely structural basis, gets complicated when multiple activation pathways and active receptor states are considered. Our unbiased, atomistic molecular dynamics simulations of the μ opioid receptor (MOP) revealed that transmission of external stimulus to the intracellular surface of the receptor is accompanied by subtle, concerted movements of highly conserved polar amino acid side chains along the 7th transmembrane helix. This may entail the rearrangement of polar species and the shift of macroscopic polarization in the transmembrane domain, triggered by agonist binding. Based on our observations and numerous independent indications, we suggest amending the widely accepted theory that the initiation event of GPCR activation is the shift of macroscopic polarization between the ortho- and allosteric binding pockets and the intracellular G protein-binding interface.

scholarly journals Universal activation mechanism of class A GPCRs

2019 ◽  
Author(s):  
Qingtong Zhou ◽  
Dehua Yang ◽  
Meng Wu ◽  
Yu Guo ◽  
Wangjing Guo ◽  
...  
Keyword(s):  
Ligand Binding ◽  
G Protein ◽  
Transmembrane Helix ◽  
Binding Pocket ◽  
Receptor Activation ◽  
Activation Mechanism ◽  
Coupling Region ◽  
Activation Pathway ◽  
Class A ◽  
Gpcr Activation

AbstractClass A G protein-coupled receptors (GPCRs) influence virtually every aspect of human physiology. GPCR activation is an allosteric process that links agonist binding to G protein recruitment, with the hallmark outward movement of transmembrane helix 6 (TM6). However, what leads to TM6 movement and the key residue-level changes of this trigger remain less well understood. Here, by analyzing over 230 high-resolution structures of class A GPCRs, we discovered a modular, universal GPCR activation pathway that unites previous findings into a common activation mechanism, directly linking the bottom of ligand-binding pocket with G protein-coupling region. We suggest that the modular nature of the universal GPCR activation pathway allowed for the decoupling of the evolution of the ligand binding site, G protein binding region and the residues important for receptor activation. Such an architecture might have facilitated GPCRs to emerge as a highly successful family of proteins for signal transduction in nature.

Conserved activation pathways in G-protein-coupled receptors

2012 ◽  
Vol 40 (2) ◽  
pp. 383-388 ◽  
Author(s):  
Xavier Deupi ◽  
Jörg Standfuss ◽  
Gebhard Schertler
Keyword(s):  
G Protein ◽  
Structural Changes ◽  
Transmembrane Helix ◽  
Pharmaceutical Research ◽  
G Protein Coupled Receptors ◽  
Activation Mechanism ◽  
Structural Basis ◽  
Structural Framework ◽  
Activation Pathways ◽  
G Protein Coupled

GPCRs (G-protein-coupled receptors) are seven-transmembrane helix proteins that transduce exogenous and endogenous signals to modulate the activity of downstream effectors inside the cell. Despite the relevance of these proteins in human physiology and pharmaceutical research, we only recently started to understand the structural basis of their activation mechanism. In the period 2008–2011, nine active-like structures of GPCRs were solved. Among them, we have determined the structure of light-activated rhodopsin with all the features of the active metarhodopsin-II, which represents so far the most native-like model of an active GPCR. This structure, together with the structures of other inactive, intermediate and active states of rhodopsin constitutes a unique structural framework on which to understand the conserved aspects of the activation mechanism of GPCRs. This mechanism can be summarized as follows: retinal isomerization triggers a series of local structural changes in the binding site that are amplified into three intramolecular activation pathways through TM (transmembrane helix) 5/TM3, TM6 and TM7/TM2. Sequence analysis strongly suggests that these pathways are conserved in other GPCRs. Differential activation of these pathways by ligands could be translated into the stabilization of different active states of the receptor with specific signalling properties.

scholarly journals Responsiveness of G protein-coupled odorant receptors is partially attributed to the activation mechanism

2015 ◽  
Vol 112 (48) ◽  
pp. 14966-14971 ◽  
Author(s):  
Yiqun Yu ◽  
Claire A. de March ◽  
Mengjue J. Ni ◽  
Kaylin A. Adipietro ◽  
Jérôme Golebiowski ◽  
...  
Keyword(s):  
G Protein ◽  
Receptor Activation ◽  
Site Directed Mutagenesis ◽  
Activation Mechanism ◽  
Odorant Receptors ◽  
Structural Basis ◽  
Single Mutation ◽  
Response Properties ◽  
Basal Activity ◽  
G Protein Coupled

Mammals detect and discriminate numerous odors via a large family of G protein-coupled odorant receptors (ORs). However, little is known about the molecular and structural basis underlying OR response properties. Using site-directed mutagenesis and computational modeling, we studied ORs sharing high sequence homology but with different response properties. When tested in heterologous cells by diverse odorants, MOR256-3 responded broadly to many odorants, whereas MOR256-8 responded weakly to a few odorants. Out of 36 mutant MOR256-3 ORs, the majority altered the responses to different odorants in a similar manner and the overall response of an OR was positively correlated with its basal activity, an indication of ligand-independent receptor activation. Strikingly, a single mutation in MOR256-8 was sufficient to confer both high basal activity and broad responsiveness to this receptor. These results suggest that broad responsiveness of an OR is at least partially attributed to its activation likelihood.

scholarly journals An Efficient Strategy to Estimate Thermodynamics and Kinetics of G Protein-Coupled Receptor Activation Using Metadynamics and Maximum Caliber

2018 ◽  
Author(s):  
Derya Meral ◽  
Davide Provasi ◽  
Marta Filizola
Keyword(s):  
G Protein ◽  
Adaptive Sampling ◽  
Receptor Activation ◽  
Conformational Space ◽  
Kinetic Properties ◽  
G Protein Coupled Receptor ◽  
Efficient Strategy ◽  
Gpcr Activation ◽  
Kinetic Rates ◽  
G Protein Coupled

ABSTRACTComputational strategies aimed at unveiling the thermodynamic and kinetic properties of G Protein-Coupled Receptor (GPCR) activation require extensive molecular dynamics simulations of the receptor embedded in an explicit lipid-water environment. A possible method for efficiently sampling the conformational space of such a complex system is metadynamics (MetaD) with path collective variables (CV). Here, we applied well-tempered MetaD with path CVs to one of the few GPCRs for which both inactive and fully active experimental structures are available, the μ-opioid receptor (MOR), and assessed the ability of this enhanced sampling method to estimate thermodynamic properties of receptor activation in line with those obtained by more computationally expensive adaptive sampling protocols. While n-body information theory (nBIT) analysis of these simulations confirmed that MetaD can efficiently characterize ligand-induced allosteric communication across the receptor, standard MetaD cannot be used directly to derive kinetic rates because transitions are accelerated by a bias potential. Applying the principle of Maximum Caliber (MaxCal) to the free-energy landscape of morphine-bound MOR reconstructed from MetaD, we obtained Markov State Models (MSMs) that yield kinetic rates of MOR activation in agreement with those obtained by adaptive sampling. Taken together, these results suggest that the MetaD-MaxCal combination creates an efficient strategy for estimating thermodynamic and kinetic properties of GPCR activation at an affordable computational cost.

scholarly journals Minireview: GPCR and G Proteins: Drug Efficacy and Activation in Live Cells

2009 ◽  
Vol 23 (5) ◽  
pp. 590-599 ◽  
Author(s):  
Jean-Pierre Vilardaga ◽  
Moritz Bünemann ◽  
Timothy N. Feinstein ◽  
Nevin Lambert ◽  
Viacheslav O. Nikolaev ◽  
...  
Keyword(s):  
Energy Transfer ◽  
G Protein ◽  
G Proteins ◽  
Intracellular Signaling ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Receptor Activation ◽  
Live Cells ◽  
Mechanical Stimuli ◽  
G Protein Coupled

Abstract Many biochemical pathways are driven by G protein-coupled receptors, cell surface proteins that convert the binding of extracellular chemical, sensory, and mechanical stimuli into cellular signals. Their interaction with various ligands triggers receptor activation that typically couples to and activates heterotrimeric G proteins, which in turn control the propagation of secondary messenger molecules (e.g. cAMP) involved in critically important physiological processes (e.g. heart beat). Successful transfer of information from ligand binding events to intracellular signaling cascades involves a dynamic interplay between ligands, receptors, and G proteins. The development of Förster resonance energy transfer and bioluminescence resonance energy transfer-based methods has now permitted the kinetic analysis of initial steps involved in G protein-coupled receptor-mediated signaling in live cells and in systems as diverse as neurotransmitter and hormone signaling. The direct measurement of ligand efficacy at the level of the receptor by Förster resonance energy transfer is also now possible and allows intrinsic efficacies of clinical drugs to be linked with the effect of receptor polymorphisms.

scholarly journals Shear stress induces Gαq/11 activation independently of G protein-coupled receptor activation in endothelial cells

2017 ◽  
Vol 312 (4) ◽  
pp. C428-C437 ◽  
Author(s):  
Nathaniel G. dela Paz ◽  
Benoît Melchior ◽  
John A. Frangos
Keyword(s):  
Endothelial Cells ◽  
Shear Stress ◽  
G Protein ◽  
Molecular Mechanisms ◽  
Fluid Shear Stress ◽  
Receptor Activation ◽  
Proximity Ligation Assay ◽  
Human Coronary Artery ◽  
Gpcr Activation ◽  
G Protein Coupled

Mechanochemical signal transduction occurs when mechanical forces, such as fluid shear stress, are converted into biochemical responses within the cell. The molecular mechanisms by which endothelial cells (ECs) sense/transduce shear stress into biological signals, including the nature of the mechanosensor, are still unclear. G proteins and G protein-coupled receptors (GPCRs) have been postulated independently to mediate mechanotransduction. In this study, we used in situ proximity ligation assay (PLA) to investigate the role of a specific GPCR/Gαq/11 pair in EC shear stress-induced mechanotransduction. We demonstrated that sphingosine 1-phosphate (S1P) stimulation causes a rapid dissociation at 0.5 min of Gαq/11 from its receptor S1P3, followed by an increased association within 2 min of GPCR kinase-2 (GRK2) and β-arrestin-1/2 with S1P3 in human coronary artery ECs, which are consistent with GPCR/Gαq/11 activation and receptor desensitization/internalization. The G protein activator AlF4 resulted in increased dissociation of Gαq/11 from S1P3, but no increase in association between S1P3 and either GRK2 or β-arrestin-1/2. The G protein inhibitor guanosine 5′-(β-thio) diphosphate (GDP-β-S) and the S1P3 antagonist VPC23019 both prevented S1P-induced activation. Shear stress also caused the rapid activation within 7 s of S1P3/Gαq/11. There were no increased associations between S1P3 and GRK2 or S1P3 and β-arrestin-1/2 until 5 min. GDP-β-S, but not VPC23019, prevented dissociation of Gαq/11 from S1P3 in response to shear stress. Shear stress did not induce rapid dephosphorylation of β-arrestin-1 or rapid internalization of S1P3, indicating no GPCR activation. These findings suggest that Gαq/11 participates in the sensing/transducing of shear stress independently of GPCR activation in ECs.

scholarly journals The mutational landscape of human olfactory G protein-coupled receptors

2020 ◽  
Author(s):  
Ramón Cierco Jimenez ◽  
Nil Casajuana-Martin ◽  
Adrián García-Recio ◽  
Lidia Alcántara ◽  
Leonardo Pardo ◽  
...  
Keyword(s):  
G Protein ◽  
Web Application ◽  
Large Family ◽  
Activation Mechanism ◽  
Human Populations ◽  
Gene Repertoire ◽  
Functional Interpretation ◽  
Gpcr Activation ◽  
Wide Range ◽  
G Protein Coupled

ABSTRACTOlfactory receptors (ORs) constitute a large family of sensory proteins that enable us to recognize a wide range of chemical volatiles in the environment. By contrast to the extensive information about human olfactory thresholds for thousands of odorants, studies of the genetic influence on olfaction are limited to a few examples. Here, we analyzed a compendium of 118,057 natural variants in human ORs collected from the public domain. OR mutations were categorized depending on their genomic and protein contexts, as well as their frequency of occurrence in several human populations. Functional interpretation of the natural changes was estimated from the increasing knowledge of the structure and function of the G protein-coupled receptor (GPCR) family, to which ORs belong. Our analysis reveals an extraordinary diversity of natural variations in the olfactory gene repertoire between individuals and populations, with a significant number of changes occurring at structural conserved regions. A particular attention is paid to mutations in positions linked to the conserved GPCR activation mechanism that could imply phenotypic variation in the olfactory perception. An interactive web application (available at http://lmc.uab.cat/hORMdb) was developed for the management and visualization of this mutational dataset.

scholarly journals The Role of ICL1 and H8 in Class B1 GPCRs; Implications for Receptor Activlation

2022 ◽  
Vol 12 ◽  
Author(s):  
Ian Winfield ◽  
Kerry Barkan ◽  
Sarah Routledge ◽  
Nathan J. Robertson ◽  
Matthew Harris ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
G Protein ◽  
Conformational Changes ◽  
Transmembrane Helix ◽  
Receptor Activation ◽  
Cgrp Receptor ◽  
Intracellular Loop ◽  
Glucagon Receptor ◽  
G Protein Coupled

The first intracellular loop (ICL1) of G protein-coupled receptors (GPCRs) has received little attention, although there is evidence that, with the 8th helix (H8), it is involved in early conformational changes following receptor activation as well as contacting the G protein β subunit. In class B1 GPCRs, the distal part of ICL1 contains a conserved R12.48KLRCxR2.46b motif that extends into the base of the second transmembrane helix; this is weakly conserved as a [R/H]12.48KL[R/H] motif in class A GPCRs. In the current study, the role of ICL1 and H8 in signaling through cAMP, iCa2+ and ERK1/2 has been examined in two class B1 GPCRs, using mutagenesis and molecular dynamics. Mutations throughout ICL1 can either enhance or disrupt cAMP production by CGRP at the CGRP receptor. Alanine mutagenesis identified subtle differences with regard elevation of iCa2+, with the distal end of the loop being particularly sensitive. ERK1/2 activation displayed little sensitivity to ICL1 mutation. A broadly similar pattern was observed with the glucagon receptor, although there were differences in significance of individual residues. Extending the study revealed that at the CRF1 receptor, an insertion in ICL1 switched signaling bias between iCa2+ and cAMP. Molecular dynamics suggested that changes in ICL1 altered the conformation of ICL2 and the H8/TM7 junction (ICL4). For H8, alanine mutagenesis showed the importance of E3908.49b for all three signal transduction pathways, for the CGRP receptor, but mutations of other residues largely just altered ERK1/2 activation. Thus, ICL1 may modulate GPCR bias via interactions with ICL2, ICL4 and the Gβ subunit.

Structural and functional aspects of G protein-coupled receptor oligomerization

1998 ◽  
Vol 76 (1) ◽  
pp. 1-11 ◽  
Author(s):  
Terence E Hébert ◽  
Michel Bouvier
Keyword(s):  
Signal Transduction ◽  
G Protein ◽  
Receptor Activation ◽  
Drug Binding ◽  
Receptor Protein ◽  
Surface Receptors ◽  
Receptor Oligomerization ◽  
Gpcr Activation ◽  
Molecular Events ◽  
G Protein Coupled

G protein-coupled receptors (GPCRs) represent the single largest family of cell surface receptors involved in signal transduction. It is estimated that several hundred distinct members of this receptor family in humans direct responses to a wide variety of chemical transmitters, including biogenic amines, amino acids, peptides, lipids, nucleosides, and large polypeptides. These transmembrane receptors are key controllers of such diverse physiological processes as neurotransmission, cellular metabolism, secretion, cellular differentiation, and growth as well as inflammatory and immune responses. GPCRs therefore represent major targets for the development of new drug candidates with potential application in all clinical fields. Many currently used therapeutics act by either activating (agonists) or blocking (antagonists) GPCRs. Studies over the past two decades have provided a wealth of information on the biochemical events underlying cellular signalling by GPCRs. However, our understanding of the molecular interactions between ligands and the receptor protein and, particularly, of the structural correlates of receptor activation or inhibition by agonists and inverse agonists, respectively, is still rudimentary. Most of the work in this area has focused on mapping regions of the receptor responsible for drug binding affinity. Although binding of ligand molecules to specific receptors represents the first event in the action of drugs, the efficacy with which this binding is translated into a physiological response remains the only determinant of therapeutic utility. In the last few years, increasing evidence suggested that receptor oligomerization and in particular dimerization may play an important role in the molecular events leading to GPCR activation. In this paper, we review the biochemical and functional evidence supporting this notion.Key words: G proteins, receptors, dimerization, signal transduction, adrenergic.

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