scholarly journals Two protonation switches control rhodopsin activation in membranes

2008 ◽  
Vol 105 (46) ◽  
pp. 17795-17800 ◽  
Author(s):  
Mohana Mahalingam ◽  
Karina Martínez-Mayorga ◽  
Michael F. Brown ◽  
Reiner Vogel
Keyword(s):  
Transmembrane Domain ◽  
Conformational Transition ◽  
Salt Bridge ◽  
Receptor Activation ◽  
Activation Mechanism ◽  
Partial Activation ◽  
Ph Dependent ◽  
G Protein Coupled ◽  
Receptor Conformation ◽  
Receptor Family

Activation of the G protein-coupled receptor (GPCR) rhodopsin is initiated by light-induced isomerization of the retinal ligand, which triggers 2 protonation switches in the conformational transition to the active receptor state Meta II. The first switch involves disruption of an interhelical salt bridge by internal proton transfer from the retinal protonated Schiff base (PSB) to its counterion, Glu-113, in the transmembrane domain. The second switch consists of uptake of a proton from the solvent by Glu-134 of the conserved E(D)RY motif at the cytoplasmic terminus of helix 3, leading to pH-dependent receptor activation. By using a combination of UV–visible and FTIR spectroscopy, we study the activation mechanism of rhodopsin in different membrane environments and show that these 2 protonation switches become partially uncoupled at physiological temperature. This partial uncoupling leads to ≈50% population of an entropy-stabilized Meta II state in which the interhelical PSB salt bridge is broken and activating helix movements have taken place but in which Glu-134 remains unprotonated. This partial activation is converted to full activation only by coupling to the pH-dependent protonation of Glu-134 from the solvent, which stabilizes the active receptor conformation by lowering its enthalpy. In a membrane environment, protonation of Glu-134 is therefore a thermodynamic rather than a structural prerequisite for activating helix movements. In light of the conservation of the E(D)RY motif in rhodopsin-like GPCRs, protonation of this carboxylate also may serve a similar function in signal transduction of other members of this receptor family.

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 Conserved Residues Control the T1R3-Specific Allosteric Signaling Pathway of the Mammalian Sweet-Taste Receptor

2019 ◽  
Vol 44 (5) ◽  
pp. 303-310 ◽  
Author(s):  
Jean-Baptiste Chéron ◽  
Amanda Soohoo ◽  
Yi Wang ◽  
Jérôme Golebiowski ◽  
Serge Antonczak ◽  
...  
Keyword(s):  
Transmembrane Domain ◽  
Taste Receptor ◽  
Receptor Activation ◽  
Sweet Taste ◽  
Site Directed Mutagenesis ◽  
Activation Mechanism ◽  
Structural Basis ◽  
Directed Mutagenesis ◽  
Conserved Residues ◽  
Sweet Taste Receptor

Abstract Mammalian sensory systems detect sweet taste through the activation of a single heteromeric T1R2/T1R3 receptor belonging to class C G-protein-coupled receptors. Allosteric ligands are known to interact within the transmembrane domain, yet a complete view of receptor activation remains elusive. By combining site-directed mutagenesis with computational modeling, we investigate the structure and dynamics of the allosteric binding pocket of the T1R3 sweet-taste receptor in its apo form, and in the presence of an allosteric ligand, cyclamate. A novel positively charged residue at the extracellular loop 2 is shown to interact with the ligand. Molecular dynamics simulations capture significant differences in the behavior of a network of conserved residues with and without cyclamate, although they do not directly interact with the allosteric ligand. Structural models show that they adopt alternate conformations, associated with a conformational change in the transmembrane region. Site-directed mutagenesis confirms that these residues are unequivocally involved in the receptor function and the allosteric signaling mechanism of the sweet-taste receptor. Similar to a large portion of the transmembrane domain, they are highly conserved among mammals, suggesting an activation mechanism that is evolutionarily conserved. This work provides a structural basis for describing the dynamics of the receptor, and for the rational design of new sweet-taste modulators.

scholarly journals A Microdomain Formed by the Extracellular Ends of the Transmembrane Domains Promotes Activation of the G Protein-Coupled α-Factor Receptor

2004 ◽  
Vol 24 (5) ◽  
pp. 2041-2051 ◽  
Author(s):  
Jennifer C. Lin ◽  
Ken Duell ◽  
James B. Konopka
Keyword(s):  
Ligand Binding ◽  
G Protein ◽  
Transmembrane Domain ◽  
Receptor Activation ◽  
G Protein Coupled Receptors ◽  
Transmembrane Domains ◽  
Consecutive Series ◽  
Subsequent Step ◽  
G Protein Coupled ◽  
Specific Reagent

ABSTRACT The α-factor receptor (Ste2p) that promotes mating in Saccharomyces cerevisiae is similar to other G protein-coupled receptors (GPCRs) in that it contains seven transmembrane domains. Previous studies suggested that the extracellular ends of the transmembrane domains are important for Ste2p function, so a systematic scanning mutagenesis was carried out in which 46 residues near the ends of transmembrane domains 1, 2, 3, 4, and 7 were replaced with cysteine. These mutants complement mutations constructed previously near the ends of transmembrane domains 5 and 6 to analyze all the extracellular ends. Eight new mutants created in this study were partially defective in signaling (V45C, N46C, T50C, A52C, L102C, N105C, L277C, and A281C). Treatment with 2-([biotinoyl] amino) ethyl methanethiosulfonate, a thiol-specific reagent that reacts with accessible cysteine residues but not membrane-embedded cysteines, identified a drop in the level of reactivity over a consecutive series of residues that was inferred to be the membrane boundary. An unusual prolonged zone of intermediate reactivity near the extracellular end of transmembrane domain 2 suggests that this region may adopt a special structure. Interestingly, residues implicated in ligand binding were mainly accessible, whereas residues involved in the subsequent step of promoting receptor activation were mainly inaccessible. These results define a receptor microdomain that provides an important framework for interpreting the mechanisms by which functionally important residues contribute to ligand binding and activation of Ste2p and other GPCRs.

scholarly journals Spatial structure of TLR4 transmembrane domain in bicelles provides the insight into the receptor activation mechanism

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Konstantin S. Mineev ◽  
Sergey A. Goncharuk ◽  
Marina V. Goncharuk ◽  
Pavel E. Volynsky ◽  
Ekaterina V. Novikova ◽  
...  
Keyword(s):  
Spatial Structure ◽  
Transmembrane Domain ◽  
Receptor Activation ◽  
Activation Mechanism ◽  
Insight Into

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 New Insights into the Signaling Mechanism of the pH-responsive, Membrane-integrated Transcriptional Activator CadC of Escherichia coli

2011 ◽  
Vol 286 (12) ◽  
pp. 10681-10689 ◽  
Author(s):  
Ina Haneburger ◽  
Andreas Eichinger ◽  
Arne Skerra ◽  
Kirsten Jung
Keyword(s):  
Escherichia Coli ◽  
Amino Acids ◽  
Amino Acid ◽  
Transmembrane Domain ◽  
Mutational Analysis ◽  
Phospholipid Composition ◽  
Receptor Activation ◽  
Activation Mechanism ◽  
Surface Patch ◽  
Repulsive Forces

The membrane-integrated transcriptional regulator CadC of Escherichia coli activates expression of the cadBA operon at low external pH with concomitantly available lysine, providing adaptation to mild acidic stress. CadC is a representative of the ToxR-like proteins that combine sensory, signal transduction, and DNA-binding activities within a single polypeptide. Although several ToxR-like regulators such as CadC, as well as the main regulator of Vibrio cholerae virulence, ToxR itself, which activate gene expression at acidic pH, have been intensively investigated, their molecular activation mechanism is still unclear. In this study, a structure-guided mutational analysis was performed to elucidate the mechanism by which CadC detects acidification of the external milieu. Thus, a cluster of negatively charged amino acids (Asp-198, Asp-200, Glu-461, Glu-468, and Asp-471) was found to be crucial for pH detection. These amino acids form a negatively charged patch on the surface of the periplasmic domain of CadC that stretches across its two subdomains. The results of different combinations of amino acid replacements within this patch indicated that the N-terminal subdomain integrates and transduces the signals coming from both subdomains to the transmembrane domain. Alterations in the phospholipid composition did not influence pH-dependent cadBA expression, and therefore, interplay of the acidic surface patch with the negatively charged headgroups is unlikely. Models are discussed according to which protonation of these acidic amino acid side chains reduces repulsive forces between the two subdomains and/or between two monomers within a CadC dimer and thereby enables receptor activation upon lowering of the environmental pH.

scholarly journals Autoantibody and hormone activation of the thyrotropin G protein-coupled receptor

2022 ◽  
Author(s):  
Bryan Faust ◽  
Isha Singh ◽  
Kaihua Zhang ◽  
Nicholas Hoppe ◽  
Antonio F.M. Pinto ◽  
...  
Keyword(s):  
Thyroid Hormones ◽  
G Protein ◽  
Conformational Changes ◽  
Hormone Receptors ◽  
Transmembrane Domain ◽  
Extracellular Domain ◽  
Receptor Activation ◽  
Glycoprotein Hormone ◽  
Membrane Bilayer ◽  
G Protein Coupled

Thyroid hormones are vital to growth and metabolism. Thyroid hormone synthesis is controlled by thyrotropin (TSH), which acts at the thyrotropin receptor (TSHR). Autoantibodies that activate the TSHR pathologically increase thyroid hormones in Graves' disease. How autoantibodies mimic TSH function remains unclear. We determined cryogenic-electron microscopy structures of active and inactive TSHR. In inactive TSHR, the extracellular domain lies close to the membrane bilayer. TSH selects an upright conformation of the extracellular domain due to steric clashes between a conserved hormone glycan and the membrane bilayer. An activating autoantibody selects a similar upright conformation of the extracellular domain. Conformational changes in the extracellular domain are transduced to the seven transmembrane domain via a conserved hinge domain, a tethered peptide agonist, and a phospholipid that binds within the seven transmembrane domain. Rotation of the TSHR ECD relative to the membrane bilayer is sufficient for receptor activation, revealing a shared mechanism for other glycoprotein hormone receptors that may also extend to G protein-coupled receptors with large extracellular domains.

scholarly journals Self-Compatible B Mutants in Coprinus With Altered Pheromone-Receptor Specificities

Genetics ◽  
2000 ◽  
Vol 156 (3) ◽  
pp. 1025-1033
Author(s):  
Natalie S Olesnicky ◽  
Andrew J Brown ◽  
Yoichi Honda ◽  
Susan L Dyos ◽  
Simon J Dowell ◽  
...  
Keyword(s):  
Amino Acid ◽  
Transmembrane Domain ◽  
Gene Mutations ◽  
Receptor Activation ◽  
Amino Acid Replacement ◽  
Single Amino Acid ◽  
Type Locus ◽  
Yeast Assay ◽  
Domain Iii ◽  
G Protein Coupled

Abstract A successful mating in the mushroom Coprinus cinereus brings together a compatible complement of pheromones and G-protein-coupled receptors encoded by multiallelic genes at the B mating-type locus. Rare B gene mutations lead to constitutive activation of B-regulated development without the need for mating. Here we characterize a mutation that arose in the B6 locus and show that it generates a mutant receptor with a single amino acid substitution (R96H) at the intracellular end of transmembrane domain III. Using a heterologous yeast assay and synthetic pheromones we show that the mutation does not make the receptor constitutively active but permits it to respond inappropriately to a normally incompatible pheromone encoded within the same B6 locus. Parallel experiments carried out in Coprinus showed that a F67W substitution in this same pheromone enabled it to activate the normally incompatible wild-type receptor. Together, our experiments show that a single amino acid replacement in either pheromone or receptor can deregulate the specificity of ligand-receptor recognition and confer a self-compatible B phenotype. In addition, we use the yeast assay to demonstrate that different receptors and pheromones found at a single B locus belong to discrete subfamilies within which receptor activation cannot normally occur.

scholarly journals A novel pH-dependent membrane peptide that binds to EphA2 and inhibits cell migration

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Daiane S Alves ◽  
Justin M Westerfield ◽  
Xiaojun Shi ◽  
Vanessa P Nguyen ◽  
Katherine M Stefanski ◽  
...  
Keyword(s):  
Cell Migration ◽  
Receptor Tyrosine Kinase ◽  
Lipid Membranes ◽  
Transmembrane Domain ◽  
Activation Mechanism ◽  
Extracellular Medium ◽  
Akt Phosphorylation ◽  
Signaling Axis ◽  
Membrane Peptide ◽  
Ph Dependent

Misregulation of the signaling axis formed by the receptor tyrosine kinase (RTK) EphA2 and its ligand, ephrinA1, causes aberrant cell-cell contacts that contribute to metastasis. Solid tumors are characterized by an acidic extracellular medium. We intend to take advantage of this tumor feature to design new molecules that specifically target tumors. We created a novel pH-dependent transmembrane peptide, TYPE7, by altering the sequence of the transmembrane domain of EphA2. TYPE7 is highly soluble and interacts with the surface of lipid membranes at neutral pH, while acidity triggers transmembrane insertion. TYPE7 binds to endogenous EphA2 and reduces Akt phosphorylation and cell migration as effectively as ephrinA1. Interestingly, we found large differences in juxtamembrane tyrosine phosphorylation and the extent of EphA2 clustering when comparing TYPE7 with activation by ephrinA1. This work shows that it is possible to design new pH-triggered membrane peptides to activate RTK and gain insights on its activation mechanism.

scholarly journals Universal Properties and Specificities of the β2-Adrenergic Receptor-Gs Protein Complex Activation Mechanism Revealed by All-Atom Molecular Dynamics Simulations

2021 ◽  
Vol 22 (19) ◽  
pp. 10423
Author(s):  
Argha Mitra ◽  
Arijit Sarkar ◽  
Attila Borics
Keyword(s):  
Adrenergic Receptor ◽  
Transmembrane Domain ◽  
Extensive Study ◽  
Activation Mechanism ◽  
Polar Species ◽  
Β2 Adrenergic Receptor ◽  
Μ Opioid Receptor ◽  
Gs Protein ◽  
Dynamics Simulations ◽  
G Protein Coupled

G protein-coupled receptors (GPCRs) are transmembrane proteins of high pharmacological relevance. It has been proposed that their activity is linked to structurally distinct, dynamically interconverting functional states and the process of activation relies on an interconnecting network of conformational switches in the transmembrane domain. However, it is yet to be uncovered how ligands with different extents of functional effect exert their actions. According to our recent hypothesis, based on indirect observations and the literature data, the transmission of the external stimulus to the intracellular surface is accompanied by the shift of macroscopic polarization in the transmembrane domain, furnished by concerted movements of highly conserved polar motifs and the rearrangement of polar species. In this follow-up study, we have examined the β2-adrenergic receptor (β2AR) to see if our hypothesis drawn from an extensive study of the μ-opioid receptor (MOP) is fundamental and directly transferable to other class A GPCRs. We have found that there are some general similarities between the two receptors, in agreement with previous studies, and there are some receptor-specific differences that could be associated with different signaling pathways.

Sign in / Sign up

Export Citation Format

Share Document