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Onaran HO, Costa T. Why classical receptor theory, which ignores allostery, can effectively measure the strength of an allosteric effect as agonist's efficacy. Br J Pharmacol 2024. [PMID: 38343142 DOI: 10.1111/bph.16327] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2023] [Revised: 12/17/2023] [Accepted: 01/07/2024] [Indexed: 02/21/2024] Open
Abstract
BACKGROUND AND PURPOSE The classical theory of receptor action has been used for decades as a powerful tool to estimate molecular determinants of ligand-induced receptor activation (i.e., affinity and efficacy) from experimentally observable biological responses. However, it is also a well-recognized fact that the receptor-binding and activation mechanisms, and the parameters thereof, described in the classical theory contradict with the modern view of receptor activation based on allosteric principles. EXPERIMENTAL APPROACH We used mathematical analysis, along with some numerical simulations, to answer the key question as to what extent the classical theory is compatible-if at all-with the modern understanding of receptor activation. KEY RESULTS Here, we showed conclusively that (1) receptor activation equations based on allosteric principles contain the logic of the classical theory in disguise, and therefore, (2) estimates of "intrinsic efficacy" (ε) obtained by means of classical techniques (i.e., null methods or fitting the operational model to concentration-response data) are equivalent to the allosteric coupling factors that represent the molecular efficacy of ligands. CONCLUSION AND IMPLICATIONS Thus, we conclude that despite the justified criticisms it has received so far, the classical theory may continue to be useful in estimating ligand efficacy from experimental data, if used properly. Here, we also provide rigorous criteria for the proper use of the theory. These findings not only have implications for ligand classification but also resolve some long lasting discussions in the field of bias agonism in GPCR, which requires reasonable estimates of relative ligand efficacies at different signalling pathways.
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Affiliation(s)
- H Ongun Onaran
- Department of Pharmacology, Faculty of Medicine, Ankara University, Ankara, Turkey
| | - Tommaso Costa
- Istituto Superiore di Sanità (retired), Viale America 111, Rome, Italy
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2
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Marmolejo-Valencia AF, Madariaga-Mazón A, Martinez-Mayorga K. Bias-inducing allosteric binding site in mu-opioid receptor signaling. SN APPLIED SCIENCES 2021. [DOI: 10.1007/s42452-021-04505-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Abstract
G-protein-biased agonism of the mu-opioid receptor (μ-OR) is emerging as a promising strategy in analgesia. A deep understanding of how biased agonists modulate and differentiate G-protein-coupled receptors (GPCR) signaling pathways and how this is transferred into the cell are open questions. Here, using extensive all-atom molecular dynamics simulations, we analyzed the binding recognition process and signaling effects of three prototype μ-OR agonists. Our suggested structural mechanism of biased signaling in μ-OR involves an allosteric sodium ion site, water networks, conformational rearrangements in conserved motifs and collective motions of loops and transmembrane helices. These analyses led us to highlight the relevance of a bias-inducing allosteric binding site in the understanding of μ-OR’s G-protein-biased signaling. These results also suggest a competitive equilibrium between the agonists and the allosteric sodium ion, where the bias-inducing allosteric binding site can be modulated by this ion or an agonist such as herkinorin. Notably, herkinorin arises as the archetype modulator of μ-OR and its interactive pattern could be used for screening efforts via protein–ligand interaction fingerprint (PLIF) studies.
Article highlights
Agonists and a sodium ion compete for the bias-inducing allosteric binding site that modulates signaling in mu-opioid receptors.
Molecular dynamics simulations of the prototype μ-OR agonist suggest a competitive equilibrium involving the agonist and an allosteric sodium ion.
Analysis of experimental data from the literature and molecular models provides the structural bases of biased agonism on μ-OR.
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3
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Onaran HO, Costa T. Conceptual and experimental issues in biased agonism. Cell Signal 2021; 82:109955. [PMID: 33607257 DOI: 10.1016/j.cellsig.2021.109955] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Revised: 01/20/2021] [Accepted: 02/14/2021] [Indexed: 12/31/2022]
Abstract
In this review, we discuss the theoretical and experimental foundations for assessing agonism in the context of signalling bias in GPCRs. We show that the formulation of efficacy in classical receptor theory and the definition of ligand-induced allosteric effect in chemical thermodynamics are coincident measures of agonism, only if we recognize that the classical model cannot be considered as a mechanistic description of the physicochemical events underlying ligand-receptor signalling. It represents instead a mathematical tool, fortuitously capable of extracting efficacy information from concentration-dependent functional data, where both ligand-dependent and ligand-independent information are present. We also assert that dissecting efficacy from affinity, as originally advocated in classical theory, is imperative for understanding the molecular property underlying agonism, and the biased agonism that leads to preferential formation of diverse GPCR-transducer complexes. Finally, we argue that beyond the assumed translational value of functional selectivity (i.e. signalling bias), the identification of ligands with true bias of efficacy is of fundamental importance for unravelling the conformational space that determines the complex functional chemistry of GPCRs.
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Affiliation(s)
- H Ongun Onaran
- Ankara University, Faculty of Medicine, Department of Pharmacology, Molecular Biology and Technology Development Unit, Ankara, Turkey.
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Abstract
Pharmacology, the chemical control of physiology, emerged as an offshoot of physiology when the physiologists using chemicals to probe physiological systems became more interested in the probes than the systems. Pharmacologists were always, and in many ways still are, bound to study drugs in systems they do not fully understand. Under these circumstances, null methods were the main ways in which conclusions about biologically active molecules were made. However, as understanding of the basic mechanisms of cellular function and biochemical systems were elucidated, so too did the understanding of how drugs affected these systems. Over the past 20 years, new ideas have emerged in the field that have completely changed and revitalized it; these are described herein. It will be seen how null methods in isolated tissues gave way to, first biochemical radioligand binding studies, and then to a wide array of functional assay technologies that can measure the effects of molecules on drug targets. In addition, the introduction of molecular dynamics, the appreciation of the allosteric nature of receptors, protein X-ray crystal structures, genetic manipulations in the form of knock-out and knock-in systems and Designer Receptors Exclusively Activated by Designer Drugs have revolutionized pharmacology.
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Affiliation(s)
- Terry Kenakin
- Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill, NC, USA.
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Abstract
INTRODUCTION The availability of different functional pharmacological assays has revealed that agonists for receptors that are pleiotropically coupled to multiple signaling pathways in the cell can emphasize signals to some pathways over others, i.e. can be biased toward certain signals. This, in turn, opens the possibility that molecules can be made to emphasize favorable signals, de-emphasize harmful signals or selectively block the ability of the natural agonist to produce unfavorable signals. Areas covered: This paper discusses the mechanism of biased signaling, the possible therapeutic implications of this effect, methods to quantify and measure bias and the current literature describing the translation of biased measure in vitro to in vivo systems. In addition, the challenges of exploiting this mechanism for therapy are outlined. Expert opinion: While this mechanism is well established and ubiquitous in pharmacology and easily measured in vitro, there are theoretical and practical hurdles to overcome to the fruitful utilization of signaling bias in therapeutic systems. There will be failures in the translation of biased molecules in vivo because of these challenges but hopefully also success and these latter translations hopefully will provide guidance in exploiting this effect further for therapy.
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Affiliation(s)
- Terry Kenakin
- a Department of Pharmacology , University of North Carolina School of Medicine , Chapel Hill , NC , USA
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6
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Kenakin TP. Synoptic pharmacology: Detecting and assessing the pharmacological significance of ligands for orphan receptors. Pharmacol Res 2016; 114:284-290. [DOI: 10.1016/j.phrs.2016.01.022] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Accepted: 01/16/2016] [Indexed: 01/14/2023]
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7
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Newton R, Giembycz MA. Understanding how long-acting β 2 -adrenoceptor agonists enhance the clinical efficacy of inhaled corticosteroids in asthma - an update. Br J Pharmacol 2016; 173:3405-3430. [PMID: 27646470 DOI: 10.1111/bph.13628] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Revised: 08/19/2016] [Accepted: 08/21/2016] [Indexed: 12/18/2022] Open
Abstract
In moderate-to-severe asthma, adding an inhaled long-acting β2 -adenoceptor agonist (LABA) to an inhaled corticosteroid (ICS) provides better disease control than simply increasing the dose of ICS. Acting on the glucocorticoid receptor (GR, gene NR3C1), ICSs promote anti-inflammatory/anti-asthma gene expression. In vitro, LABAs synergistically enhance the maximal expression of many glucocorticoid-induced genes. Other genes, including dual-specificity phosphatase 1(DUSP1) in human airways smooth muscle (ASM) and epithelial cells, are up-regulated additively by both drug classes. Synergy may also occur for LABA-induced genes, as illustrated by the bronchoprotective gene, regulator of G-protein signalling 2 (RGS2) in ASM. Such effects cannot be produced by either drug alone and may explain the therapeutic efficacy of ICS/LABA combination therapies. While the molecular basis of synergy remains unclear, mechanistic interpretations must accommodate gene-specific regulation. We explore the concept that each glucocorticoid-induced gene is an independent signal transducer optimally activated by a specific, ligand-directed, GR conformation. In addition to explaining partial agonism, this realization provides opportunities to identify novel GR ligands that exhibit gene expression bias. Translating this into improved therapeutic ratios requires consideration of GR density in target tissues and further understanding of gene function. Similarly, the ability of a LABA to interact with a glucocorticoid may be suboptimal due to low β2 -adrenoceptor density or biased β2 -adrenoceptor signalling. Strategies to overcome these limitations include adding-on a phosphodiesterase inhibitor and using agonists of other Gs-coupled receptors. In all cases, the rational design of ICS/LABA, and derivative, combination therapies requires functional knowledge of induced (and repressed) genes for therapeutic benefit to be maximized.
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Affiliation(s)
- Robert Newton
- Department of Cell Biology and Anatomy, Airways Inflammation Research Group, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
| | - Mark A Giembycz
- Department of Physiology and Pharmacology, Airways Inflammation Research Group, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
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8
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Bock A, Bermudez M, Krebs F, Matera C, Chirinda B, Sydow D, Dallanoce C, Holzgrabe U, De Amici M, Lohse MJ, Wolber G, Mohr K. Ligand Binding Ensembles Determine Graded Agonist Efficacies at a G Protein-coupled Receptor. J Biol Chem 2016; 291:16375-89. [PMID: 27298318 PMCID: PMC4965584 DOI: 10.1074/jbc.m116.735431] [Citation(s) in RCA: 62] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2016] [Revised: 06/07/2016] [Indexed: 11/06/2022] Open
Abstract
G protein-coupled receptors constitute the largest family of membrane receptors and modulate almost every physiological process in humans. Binding of agonists to G protein-coupled receptors induces a shift from inactive to active receptor conformations. Biophysical studies of the dynamic equilibrium of receptors suggest that a portion of receptors can remain in inactive states even in the presence of saturating concentrations of agonist and G protein mimetic. However, the molecular details of agonist-bound inactive receptors are poorly understood. Here we use the model of bitopic orthosteric/allosteric (i.e. dualsteric) agonists for muscarinic M2 receptors to demonstrate the existence and function of such inactive agonist·receptor complexes on a molecular level. Using all-atom molecular dynamics simulations, dynophores (i.e. a combination of static three-dimensional pharmacophores and molecular dynamics-based conformational sampling), ligand design, and receptor mutagenesis, we show that inactive agonist·receptor complexes can result from agonist binding to the allosteric vestibule alone, whereas the dualsteric binding mode produces active receptors. Each agonist forms a distinct ligand binding ensemble, and different agonist efficacies depend on the fraction of purely allosteric (i.e. inactive) versus dualsteric (i.e. active) binding modes. We propose that this concept may explain why agonist·receptor complexes can be inactive and that adopting multiple binding modes may be generalized also to small agonists where binding modes will be only subtly different and confined to only one binding site.
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Affiliation(s)
- Andreas Bock
- From the Institute of Pharmacology and Toxicology, University of Würzburg, Versbacher Strasse 9, 97078 Würzburg, Germany,
| | - Marcel Bermudez
- Institute of Pharmacy, Freie Universität Berlin, Königin-Luise-Strasse 2 und 4, 14195 Berlin, Germany,
| | - Fabian Krebs
- Pharmacology and Toxicology Section, Institute of Pharmacy, University of Bonn, Gerhard-Domagk-Strasse 3, 53121 Bonn, Germany
| | - Carlo Matera
- Dipartimento di Scienze Farmaceutiche, Sezione di Chimica Farmaceutica "Pietro Pratesi," Università degli Studi di Milano, Via Mangiagalli 25, 20133 Milan, Italy, and
| | - Brian Chirinda
- Pharmacology and Toxicology Section, Institute of Pharmacy, University of Bonn, Gerhard-Domagk-Strasse 3, 53121 Bonn, Germany
| | - Dominique Sydow
- Institute of Pharmacy, Freie Universität Berlin, Königin-Luise-Strasse 2 und 4, 14195 Berlin, Germany
| | - Clelia Dallanoce
- Dipartimento di Scienze Farmaceutiche, Sezione di Chimica Farmaceutica "Pietro Pratesi," Università degli Studi di Milano, Via Mangiagalli 25, 20133 Milan, Italy, and
| | - Ulrike Holzgrabe
- Institute of Pharmacy, University of Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Marco De Amici
- Dipartimento di Scienze Farmaceutiche, Sezione di Chimica Farmaceutica "Pietro Pratesi," Università degli Studi di Milano, Via Mangiagalli 25, 20133 Milan, Italy, and
| | - Martin J Lohse
- From the Institute of Pharmacology and Toxicology, University of Würzburg, Versbacher Strasse 9, 97078 Würzburg, Germany
| | - Gerhard Wolber
- Institute of Pharmacy, Freie Universität Berlin, Königin-Luise-Strasse 2 und 4, 14195 Berlin, Germany
| | - Klaus Mohr
- Pharmacology and Toxicology Section, Institute of Pharmacy, University of Bonn, Gerhard-Domagk-Strasse 3, 53121 Bonn, Germany,
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9
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Abstract
Over the past 50 years in pharmacology, an understanding of seven transmembrane (7TMR) function has been gained from the comparison of experimental data to receptor models. These models have been constructed from building blocks composed of systems consisting of series and parallel mass action binding reactions. Basic functions such as the the isomerization of receptors upon ligand binding, the sequential binding of receptors to membrane coupling proteins, and the selection of multiple receptor conformations have been combined in various ways to build receptor systems such as the ternary complex, extended ternary complex, and cubic ternary complex models for 7TMR function. Separately, the Black/Leff operational model has furnished an extremely valuable method of quantifying drug agonism. In the past few years, incorporation of the basic allosteric nature of 7TMRs has led to additional useful models of functional receptor allosteric mechanisms; these models yield valuable methods for quantifying allosteric effects. Finally, molecular dynamics has provided yet another new set of models describing the probability of formation of multiple receptor states; these radically new models are extremely useful in the prediction of functionally selective drug effects.
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Affiliation(s)
- Terry Kenakin
- Department of Pharmacology, University of North Carolina School of Medicine , 120 Mason Farm Road, Room 4042, Genetic Medicine Building, CB# 7365, Chapel Hill, North Carolina 27599-7365, United States
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10
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Hauser MA, Legler DF. Common and biased signaling pathways of the chemokine receptor CCR7 elicited by its ligands CCL19 and CCL21 in leukocytes. J Leukoc Biol 2016; 99:869-82. [PMID: 26729814 DOI: 10.1189/jlb.2mr0815-380r] [Citation(s) in RCA: 127] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2015] [Accepted: 12/17/2015] [Indexed: 12/24/2022] Open
Abstract
Chemokines are pivotal regulators of cell migration during continuous immune surveillance, inflammation, homeostasis, and development. Chemokine binding to their 7-transmembrane domain, G-protein-coupled receptors causes conformational changes that elicit intracellular signaling pathways to acquire and maintain an asymmetric architectural organization and a polarized distribution of signaling molecules necessary for directional cell migration. Leukocytes rely on the interplay of chemokine-triggered migration modules to promote amoeboid-like locomotion. One of the most important chemokine receptors for adaptive immune cell migration is the CC-chemokine receptor CCR7. CCR7 and its ligands CCL19 and CCL21 control homing of T cells and dendritic cells to areas of the lymph nodes where T cell priming and the initiation of the adaptive immune response occur. Moreover, CCR7 signaling also contributes to T cell development in the thymus and to lymphorganogenesis. Although the CCR7-CCL19/CCL21 axis evolved to benefit the host, inappropriate regulation or use of these proteins can contribute or cause pathobiology of chronic inflammation, tumorigenesis, and metastasis, as well as autoimmune diseases. Therefore, it appears as the CCR7-CCL19/CCL21 axis is tightly regulated at numerous intersections. Here, we discuss the multiple regulatory mechanism of CCR7 signaling and its influence on CCR7 function. In particular, we focus on the functional diversity of the 2 CCR7 ligands, CCL19 and CCL21, as well as on their impact on biased signaling. The understanding of the molecular determinants of biased signaling and the multiple layers of CCR7 regulation holds the promise for potential future therapeutic intervention.
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Affiliation(s)
- Mark A Hauser
- Biotechnology Institute Thurgau at the University of Konstanz, Kreuzlingen, Switzerland
| | - Daniel F Legler
- Biotechnology Institute Thurgau at the University of Konstanz, Kreuzlingen, Switzerland
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11
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Chidiac P. RGS proteins destroy spare receptors: Effects of GPCR-interacting proteins and signal deamplification on measurements of GPCR agonist potency. Methods 2016; 92:87-93. [DOI: 10.1016/j.ymeth.2015.08.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2015] [Revised: 08/13/2015] [Accepted: 08/14/2015] [Indexed: 12/15/2022] Open
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12
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Kenakin T. The mass action equation in pharmacology. Br J Clin Pharmacol 2015; 81:41-51. [PMID: 26506455 DOI: 10.1111/bcp.12810] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2015] [Revised: 09/25/2015] [Accepted: 10/12/2015] [Indexed: 01/14/2023] Open
Abstract
The mass action equation is the building block from which all models of drug-receptor interaction are built. In the simplest case, the equation predicts a sigmoidal relationship between the amount of drug-receptor complex and the logarithm of the concentration of drug. The form of this function is also the same as most dose-response relationships in pharmacology (such as enzyme inhibition and the protein binding of drugs) but the potency term in dose-response relationships very often differs in meaning from the similar term in the simple mass action relationship. This is because (i) most pharmacological systems are collections of mass action reactions in series and/or in parallel and (ii) the important assumptions in the mass action reaction are violated in complex pharmacological systems. In some systems, the affinity of the receptor R for some ligand A is modified by interaction of the receptor with the allosteric ligand B and concomitantly the affinity of the receptor for ligand B is modified to the same degree. When this occurs, the observed affinity of the ligand A for the receptor will depend on both the concentration of the co-binding allosteric ligand and its nature. The relationships between drug potency in pharmacological models and the equilibrium dissociation constants defined in single mass action reactions are discussed. More detailed knowledge of efficacy has led to new models of drug action that depend on the relative probabilities of different states, and these have taken knowledge of drug-receptor interactions beyond Guldberg and Waage.
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Affiliation(s)
- Terry Kenakin
- Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill, NC, USA
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13
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Kenakin T. Gaddum Memorial Lecture 2014: receptors as an evolving concept: from switches to biased microprocessors. Br J Pharmacol 2015; 172:4238-53. [PMID: 26075971 DOI: 10.1111/bph.13217] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2015] [Revised: 03/06/2015] [Accepted: 03/16/2015] [Indexed: 12/17/2022] Open
Abstract
This review is based on the JR Vane Medal Lecture presented at the BPS Winter Meeting in December 2014 by T. Kenakin. A recording of the lecture is included as supporting information and can also be viewed online here: https://www.youtube.com/watch?v=xrP81AQ8l-8. Pharmacological models used to describe drug agonism and antagonism have evolved over the past 20 years from a parsimonious model describing single active and inactive receptor states to models of multiconformational receptor systems modified by ligand conformational selection. These latter models describe the observed, presently underexploited, pharmacological mechanism of ligand-directed biased signalling. Biased signals can be quantified with transduction coefficients (ΔΔLog(τ/KA) values), a scale grounded in the Black/Leff operational model; this enables the optimization of biased profiles through medicinal chemistry. The past decades have also brought the availability of new technologies to measure multiple functional effects mediated by seven transmembrane receptors. These have confirmed that drugs can have many efficacies, which may be collaterally linked, that is there is no linear sequence of activities required. In addition, new functional screening assays have introduced increasing numbers of allosteric ligands into drug discovery. These molecules are permissive (they do not necessarily preclude endogenous signalling in vivo); therefore, they may allow better fine tuning of pathological physiology. The permissive quality of allosteric ligands can also change the quality of endogenous signalling efficacy ('induced bias') as well as the quantity of signal; in this regard, indices related to ΔΔLog(τ/KA) values (namely ΔLog(αβ) values) can be used to quantify these effects for optimization in the drug discovery process. All of these added scales of drug activity will, hopefully, allow better targeting of candidate molecules towards therapies.
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Affiliation(s)
- Terry Kenakin
- Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill, NC, USA
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14
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Kenakin T. The Effective Application of Biased Signaling to New Drug Discovery. Mol Pharmacol 2015; 88:1055-61. [PMID: 26138073 DOI: 10.1124/mol.115.099770] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2015] [Accepted: 07/02/2015] [Indexed: 01/14/2023] Open
Abstract
The ability of agonists to selectively activate some but not all signaling pathways linked to pleiotropically signaling receptors has opened the possibility of obtaining molecules that emphasize beneficial signals, de-emphasize harmful signals, and concomitantly deemphasize harmful signals while blocking the harmful signals produced by endogenous agonists. The detection and quantification of biased effects is straightforward, but two important factors should be considered in the evaluation of biased effects in drug discovery. The first is that efficacy, and not bias, determines whether a given agonist signal will be observed; bias only dictates the relative concentrations at which agonist signals will appear when they do appear. Therefore, a Cartesian coordinate system plotting relative efficacy (on a scale of Log relative Intrinsic Activities) as the ordinates and Log(bias) as the abscissae is proposed as a useful tool in evaluating possible biased molecules for progression in discovery programs. Second, it should be considered that the current scales quantifying bias limit this property to the allosteric vector (ligand/receptor/coupling protein complex) and that whole-cell processing of this signal can completely change measured bias from in vitro predictions.
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Affiliation(s)
- Terry Kenakin
- Department of Pharmacology, School of Medicine, University of North Carolina, Chapel Hill, North Carolina
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15
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What is pharmacological 'affinity'? Relevance to biased agonism and antagonism. Trends Pharmacol Sci 2014; 35:434-41. [PMID: 25042457 DOI: 10.1016/j.tips.2014.06.003] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2014] [Revised: 06/16/2014] [Accepted: 06/17/2014] [Indexed: 11/22/2022]
Abstract
The differences between affinity measurements made in binding studies and those relevant to receptor function are described. There are theoretical and practical reasons for not utilizing binding data and, in terms of the quantification of signaling bias, it is unnecessary to do so. Finally, the allosteric control of ligand affinity through receptor-signaling protein interaction is discussed within the context of biased antagonism. In this regard, it is shown that both the bias and relative efficacy of a ligand are essential data for fully predicting biased effects in vivo.
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16
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Strachan RT, Sun JP, Rominger DH, Violin JD, Ahn S, Rojas Bie Thomsen A, Zhu X, Kleist A, Costa T, Lefkowitz RJ. Divergent transducer-specific molecular efficacies generate biased agonism at a G protein-coupled receptor (GPCR). J Biol Chem 2014; 289:14211-24. [PMID: 24668815 PMCID: PMC4022887 DOI: 10.1074/jbc.m114.548131] [Citation(s) in RCA: 98] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2014] [Revised: 03/12/2014] [Indexed: 01/06/2023] Open
Abstract
The concept of "biased agonism" arises from the recognition that the ability of an agonist to induce a receptor-mediated response (i.e. "efficacy") can differ across the multiple signal transduction pathways (e.g. G protein and β-arrestin (βarr)) emanating from a single GPCR. Despite the therapeutic promise of biased agonism, the molecular mechanism(s) whereby biased agonists selectively engage signaling pathways remain elusive. This is due in large part to the challenges associated with quantifying ligand efficacy in cells. To address this, we developed a cell-free approach to directly quantify the transducer-specific molecular efficacies of balanced and biased ligands for the angiotensin II type 1 receptor (AT1R), a prototypic GPCR. Specifically, we defined efficacy in allosteric terms, equating shifts in ligand affinity (i.e. KLo/KHi) at AT1R-Gq and AT1R-βarr2 fusion proteins with their respective molecular efficacies for activating Gq and βarr2. Consistent with ternary complex model predictions, transducer-specific molecular efficacies were strongly correlated with cellular efficacies for activating Gq and βarr2. Subsequent comparisons across transducers revealed that biased AT1R agonists possess biased molecular efficacies that were in strong agreement with the signaling bias observed in cellular assays. These findings not only represent the first measurements of the thermodynamic driving forces underlying differences in ligand efficacy between transducers but also support a molecular mechanism whereby divergent transducer-specific molecular efficacies generate biased agonism at a GPCR.
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Affiliation(s)
- Ryan T Strachan
- From the Department of Medicine, Duke University, Medical Center, Durham, North Carolina 27710
| | - Jin-peng Sun
- Key Laboratory of Experimental Teratology of the Ministry of Education, Department of Biochemistry and Molecular Biology, Shandong University, School of Medicine, Jinan, Shandong 250012, China
| | | | | | - Seungkirl Ahn
- From the Department of Medicine, Duke University, Medical Center, Durham, North Carolina 27710
| | - Alex Rojas Bie Thomsen
- From the Department of Medicine, Duke University, Medical Center, Durham, North Carolina 27710
| | - Xiao Zhu
- From the Department of Medicine, Duke University, Medical Center, Durham, North Carolina 27710
| | - Andrew Kleist
- From the Department of Medicine, Duke University, Medical Center, Durham, North Carolina 27710
| | - Tommaso Costa
- Dipartimento del Farmaco, Istituto Superiore di Sanita, 00161 Rome, Italy,
| | - Robert J Lefkowitz
- From the Department of Medicine, Duke University, Medical Center, Durham, North Carolina 27710, Department of Biochemistry, Duke University, Medical Center, Durham, North Carolina 27710, and Howard Hughes Medical Institute, Duke University, Medical Center, Durham, North Carolina 27710
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Shonberg J, Lopez L, Scammells PJ, Christopoulos A, Capuano B, Lane JR. Biased Agonism at G Protein-Coupled Receptors: The Promise and the Challenges-A Medicinal Chemistry Perspective. Med Res Rev 2014; 34:1286-330. [DOI: 10.1002/med.21318] [Citation(s) in RCA: 87] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Jeremy Shonberg
- Medicinal Chemistry; Monash Institute of Pharmaceutical Sciences; Monash University (Parkville Campus); Parkville Victoria Australia
| | - Laura Lopez
- Drug Discovery Biology; Monash Institute of Pharmaceutical Sciences; Monash University (Parkville Campus); Parkville Victoria Australia
| | - Peter J. Scammells
- Medicinal Chemistry; Monash Institute of Pharmaceutical Sciences; Monash University (Parkville Campus); Parkville Victoria Australia
| | - Arthur Christopoulos
- Drug Discovery Biology; Monash Institute of Pharmaceutical Sciences; Monash University (Parkville Campus); Parkville Victoria Australia
| | - Ben Capuano
- Medicinal Chemistry; Monash Institute of Pharmaceutical Sciences; Monash University (Parkville Campus); Parkville Victoria Australia
| | - J. Robert Lane
- Drug Discovery Biology; Monash Institute of Pharmaceutical Sciences; Monash University (Parkville Campus); Parkville Victoria Australia
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18
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Abstract
In the present study, we show that inverse agonists at histamine H2 receptors display positive efficacy regarding receptor desensitization/internalization and ERK1/2 phosphorylation. These findings demonstrate that histamine receptor ligands show functional selectivity respect to distinct receptor behaviours.
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Abstract
It is now established that agonists do not uniformly activate pleiotropic signaling mechanisms initiated by receptors but rather can bias signals according to the unique receptor conformations they stabilize. One of the important emerging signaling systems where this can occur is through β-arrestin. This chapter discusses biased signaling where emphasis or de-emphasis of β-arrestin signaling is postulated (or been shown) to be beneficial. The chapter specifically focuses on methods to quantify biased effects; these methods furnish scales that can be used in the process of optimizing biased agonism (and antagonism) for therapeutic benefit. Specifically, methods to derive ΔΔLog(τ/K A) or ΔΔLog(Relative Activity) values are described to do this.
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Affiliation(s)
- Terry Kenakin
- Department of Pharmacology, University of North Carolina School of Medicine, 120 Mason Farm Road, Room 4042, Genetic Medicine Building, CB# 7365, Chapel Hill, NC, 27599-7365, USA,
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Pernomian L, Gomes MS, Restini CBA, Pupo AS, de Oliveira AM. Cross-talk with β2 -adrenoceptors enhances ligand affinity properties from endothelial alpha1 D -adrenoceptors that mediates carotid relaxation. ACTA ACUST UNITED AC 2013; 65:1337-46. [PMID: 23927472 DOI: 10.1111/jphp.12105] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2013] [Accepted: 06/18/2013] [Indexed: 12/01/2022]
Abstract
OBJECTIVES Our main objectives were to investigate the affinity properties of endothelial and muscular α1D -adrenoceptors and to characterize the cross-talk between endothelial α1D -adrenoceptors and β2 -adrenoceptors in rat carotid. METHODS Relaxation and contraction concentration-response curves for phenylephrine (α1 -adrenergic agonist) were obtained in carotid rings in absence or presence of increasing concentrations of BMY7378 (α1D -adrenergic antagonist), combined or not with increasing concentration of ICI-118,551 (β2 -adrenergic antagonist). Schild analysis was used to estimate the affinity constant from pA2 values of BMY7378. KEY FINDINGS BMY7378 produced an unsurmountable antagonism on phenylephrine-induced relaxation but a surmountable antagonism on phenylephrine-induced contraction. BMY7378 potency was higher in inhibiting the relaxation than the contraction induced by phenylephrine because the rightward shifts induced by BMY7378 were greater in the relaxation. The apparent pA2 value for BMY7378 in phenylephrine-induced relaxation was greater than in contraction. When combined with ICI-118,551, BMY7378 yielded a surmountable antagonism on phenylephrine-induced relaxation and presented a pA2 value similar to that obtained in phenylephrine-induced contraction. CONCLUSIONS Endothelial α1D -adrenoceptors, which mediates rat carotid relaxation, present high ligand affinity because of the cross-talk with β2 -adrenoceptors, which explains the higher potency of phenylephrine in inducing relaxation than contraction and the atypical unsurmountable antagonism produced by BMY7378 on phenylephrine-induced relaxation.
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Affiliation(s)
- Larissa Pernomian
- Faculty of Pharmaceutical Sciences from Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo, Brazil.
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Antihistaminergics and inverse agonism: potential therapeutic applications. Eur J Pharmacol 2013; 715:26-32. [PMID: 23831018 DOI: 10.1016/j.ejphar.2013.06.027] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2013] [Revised: 06/07/2013] [Accepted: 06/21/2013] [Indexed: 12/19/2022]
Abstract
The accurate characterization of the molecular mechanisms involved in the action of receptor ligands is important for their appropriate therapeutic use and safety. It is well established that ligands acting at the histamine system currently used in the clinic exert their actions by specifically antagonizing G-protein coupled H1 and H2 receptors. However, most of these ligands, assumed to be neutral antagonists, behave as inverse agonists displaying negative efficacy in experimental systems. This suggests that their therapeutic actions may involve not only receptor blockade, but also the decrease of spontaneous receptor activity. The mechanisms whereby inverse agonists achieve negative efficacy are diverse. Theoretical models predict at least three possible mechanisms, all of which are supported by experimental observations. Depending on the mechanism of action engaged, the inverse agonist could interfere specifically with signaling events triggered by unrelated receptors. This possibility opens up new venues to explain the therapeutic actions of inverse agonists of the histamine receptor and perhaps new therapeutic applications.
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Kenakin T. New concepts in pharmacological efficacy at 7TM receptors: IUPHAR review 2. Br J Pharmacol 2013; 168:554-75. [PMID: 22994528 PMCID: PMC3579279 DOI: 10.1111/j.1476-5381.2012.02223.x] [Citation(s) in RCA: 119] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2012] [Revised: 08/03/2012] [Accepted: 09/12/2012] [Indexed: 01/14/2023] Open
Abstract
The present-day concept of drug efficacy has changed completely from its original description as the property of agonists that causes tissue activation. The ability to visualize the multiple behaviours of seven transmembrane receptors has shown that drugs can have many efficacies and also that the transduction of drug stimulus to various cellular stimulus-response cascades can be biased towards some but not all pathways. This latter effect leads to agonist 'functional selectivity', which can be favourable for the improvement of agonist therapeutics. However, in addition, biased agonist potency becomes cell type dependent with the loss of the monotonic behaviour of stimulus-response mechanisms, leading to potential problems in agonist quantification. This has an extremely important effect on the discovery process for new agonists since it now cannot be assumed that a given screening or lead optimization assay will correctly predict therapeutic behaviour. This review discusses these ideas and how new approaches to quantifying agonist effect may be used to circumvent the cell type dependence of agonism. This article, written by a corresponding member of the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification (NC-IUPHAR), reviews our current understanding of the interaction of ligands with seven transmembrane receptors. Further information on these pharmacological concepts is being incorporated into the IUPHAR/BPS database GuideToPharmacology.org.
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Affiliation(s)
- Terry Kenakin
- Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill, NC, USA.
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Hall DA. Application of receptor theory to allosteric modulation of receptors. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2013; 115:217-90. [PMID: 23415096 DOI: 10.1016/b978-0-12-394587-7.00006-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
In this chapter, three topics are considered. The allosteric two-state model (ATSM) is compared with explicit multiconformational models. This demonstrates that the ATSM encapsulates the common behaviors of any model with at least two active and two inactive conformations: the "states" of the model represent ensembles of active and inactive conformations. A matrix representation of multiconformational models is introduced to provide a compact notation for models with arbitrarily large numbers of conformations. Allosteric modulation is further explored in the context of an operational model of receptor activity which includes constitutive receptor activity. Fitting this model allows the apparent affinity, intrinsic efficacy, and cooperativity constants of a pair of allosteric ligands to be determined. It is also demonstrated that, within certain limits, it is possible to estimate the parameters of the ATSM. Finally, a novel operational model is developed that may allow the analysis of protean ligands. This model requires a nonlinear stimulus function and two parameters to define the efficacy of a ligand. Expressions describing competitive and allosteric interactions under this model are developed and the results of applying null analyses to the data are determined.
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Affiliation(s)
- David A Hall
- Fibrosis DPU, GlaxoSmithKline, Stevenage, Herts, United Kingdom
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Kenakin TP. Biased signalling and allosteric machines: new vistas and challenges for drug discovery. Br J Pharmacol 2012; 165:1659-1669. [PMID: 22023017 DOI: 10.1111/j.1476-5381.2011.01749.x] [Citation(s) in RCA: 179] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Seven transmembrane receptors (7TMRs) are nature's prototype allosteric proteins made to bind molecules at one location to subsequently change their shape to affect the binding of another molecule at another location. This paper attempts to describe the divergent 7TMR behaviours (i.e. third party allostery, receptor oligomerization, biased agonism) observed in pharmacology in terms of a homogeneous group of allosteric behaviours. By considering the bodies involved as a vector defined by a modulator, conduit and guest, these activities can all be described by a simple model of functional allostery made up of the Ehlert allosteric model and the Black/Leff operational model. It will be shown how this model yields parameters that can be used to characterize the activity of any ligand or protein producing effect through allosteric interaction with a 7TMR.
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Affiliation(s)
- Terry P Kenakin
- Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina, USA
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Abstract
Receptor theory assigns mathematical rules to biological systems in order to quantify drug effects and define what biological systems can and cannot do, leading to the design of experiments that may further modify the model. Drug receptor theory also furnishes the tools for quantifying the activity of drugs in a system-independent manner, essential because drugs are almost always studied in test systems somewhat removed from the therapeutic system for which they are intended. Since biological systems operate at different set points in the body under different conditions, the ability to predict drug effects under a variety of circumstances is important. This unit provides a historical perspective of classical receptor theory and the currently used operational model of drug effects. The mechanism of drug receptor function is also described in terms of the various iterations of the ternary complex model, the two-state theory for ion channels, and a probabilistic model of multiple receptor conformations.
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Affiliation(s)
- Terry Kenakin
- GlaxoSmithKline Research Institute, Research Triangle Park, North Carolina, USA
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Fanelli F, De Benedetti PG. Update 1 of: computational modeling approaches to structure-function analysis of G protein-coupled receptors. Chem Rev 2011; 111:PR438-535. [PMID: 22165845 DOI: 10.1021/cr100437t] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Francesca Fanelli
- Dulbecco Telethon Institute, University of Modena and Reggio Emilia, via Campi 183, 41125 Modena, Italy.
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Shenker A. Activating Mutations of the Lutropin Choriogonadotropin Receptor in Precocious Puberty. ACTA ACUST UNITED AC 2011. [DOI: 10.3109/10606820212138] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Abstract
Increasing numbers of compounds, previously classified as antagonists, were shown to inhibit this spontaneous or constitutive receptor activity, instead of leave it unaffected as expected for a formal antagonist. In addition, some other antagonists did not have any effect by themselves, but prevented the inhibition of constitutive activity induced by thought-to-be antagonists. These thought-to-be antagonists with negative efficacy are now known as "inverse agonists." Inverse agonism at βAR has been evidenced for both subtypes in wild-type GPCRs systems and in engineered systems with high constitutive activity. It is important to mention that native systems are of particular importance for analyzing the in vivo relevance of constitutive activity because these systems have physiological expression levels of target receptors. Studies of inverse agonism of β blockers in physiological setting have also evidenced that pathophysiological conditions can affect pharmacodynamic properties of these ligands. To date, hundreds of clinically well-known drugs have been tested and classified for this property. Prominent examples include the beta-blockers propranolol, alprenolol, pindolol, and timolol used for treating hypertension, angina pectoris, and arrhythmia that act on the β₂ARs, metoprolol, and bisoprolol used for treating hypertension, coronary heart disease, and arrhythmias by acting on β₁ARs. Inverse agonists seem to be useful in the treatment of chronic disease characterized by harmful effects resulting from β₁AR and β₂AR overactivation, such as heart failure and asthma, respectively.
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Affiliation(s)
- Carlos A Taira
- Cátedra de Farmacología, Instituto de Fisiopatología y Bioquímica Clínica, Universidad de Buenos Aires, CONICET, Junín 956, Buenos Aires, Argentina
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Kenakin T. Allosteric theory: taking therapeutic advantage of the malleable nature of GPCRs. Curr Neuropharmacol 2010; 5:149-56. [PMID: 19305797 PMCID: PMC2656818 DOI: 10.2174/157015907781695973] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2006] [Accepted: 04/05/2007] [Indexed: 12/02/2022] Open
Abstract
The description of the allosteric modification of receptors to affect changes in their function requires a model that considers the effects of the modulator on both agonist affinity and efficacy. A model is presented which describes changes in affinity in terms of the constant α (ratio of affinity in the presence vs the absence of modulator) and also the constant ξ (ratio of intrinsic efficacy of the agonist in the presence vs absence of modulator). This allows independent effects of both affinity and efficacy and allows the modeling of any change in the dose-response curve to an agonist after treatment with modulator. Examples are given where this type of model can predict effects of modulators that reduce efficacy but actually increase affinity of agonist (i.e. ifenprodil) and also of modulators that block the action of some agonists (the CXCR4 agonist SDF-1α by the antagonist AMD3100) but not others for the same receptor (SDF-1α peptide fragments RSVM and ASLW). ‘All models are wrong…but some are useful…’ anonymous environmental scientist
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Affiliation(s)
- Terry Kenakin
- Dept. of Biological Reagents and Assay Develpoment, GlaxoSmithKline Research and Development, 5 Moore Drive, Research Triangle Park, NC 27709, USA.
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Kenakin T, Miller LJ. Seven transmembrane receptors as shapeshifting proteins: the impact of allosteric modulation and functional selectivity on new drug discovery. Pharmacol Rev 2010; 62:265-304. [PMID: 20392808 DOI: 10.1124/pr.108.000992] [Citation(s) in RCA: 458] [Impact Index Per Article: 32.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
It is useful to consider seven transmembrane receptors (7TMRs) as disordered proteins able to allosterically respond to a number of binding partners. Considering 7TMRs as allosteric systems, affinity and efficacy can be thought of in terms of energy flow between a modulator, conduit (the receptor protein), and a number of guests. These guests can be other molecules, receptors, membrane-bound proteins, or signaling proteins in the cytosol. These vectorial flows of energy can yield standard canonical guest allostery (allosteric modification of drug effect), effects along the plane of the cell membrane (receptor oligomerization), or effects directed into the cytosol (differential signaling as functional selectivity). This review discusses these apparently diverse pharmacological effects in terms of molecular dynamics and protein ensemble theory, which tends to unify 7TMR behavior toward cells. Special consideration will be given to functional selectivity (biased agonism and biased antagonism) in terms of mechanism of action and potential therapeutic application. The explosion of technology that has enabled observation of diverse 7TMR behavior has also shown how drugs can have multiple (pluridimensional) efficacies and how this can cause paradoxical drug classification and nomenclatures.
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Affiliation(s)
- Terry Kenakin
- GlaxoSmithKline, 5 Moore Drive, Mailtstop V-287, Research Triangle Park, NC 27709, USA.
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Kenakin TP. Cellular assays as portals to seven-transmembrane receptor-based drug discovery. Nat Rev Drug Discov 2009; 8:617-26. [PMID: 19609267 DOI: 10.1038/nrd2838] [Citation(s) in RCA: 134] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
As technology advances to the point at which various behaviours of seven-transmembrane (7TM) receptors (also known as G protein-coupled receptors (GPCRs)) can be observed individually, it is clear that, rather than being 'on-off' switches, 7TM receptors are more akin to 'microprocessors' of information. This has introduced the phenomenon of functional selectivity, whereby certain ligands initiate only portions of the signalling mechanisms mediated by a given receptor, which has opened new horizons for drug discovery. The need to discover new 7TM receptor-ligand behaviours and quantify the effect of the drug on these complex systems, to guide medicinal chemistry, puts the pharmacological assay into the spotlight. This Perspective outlines the return to whole-system assays from reductionist recombinant systems, and discusses how the efficacy of a drug is linked to the particular assay used to observe its effects. It also highlights how these new assays are adding value to the drug discovery process.
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Affiliation(s)
- Terry P Kenakin
- Department of Biological Reagents and Assay Development, GlaxoSmithKline Research and Development, 5 Moore Drive, Research Triangle Park, NC 27709, USA.
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34
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Kenakin T. Interrogating 7TM receptors: Does texture in the question yield greater texture in the answer? J Recept Signal Transduct Res 2009; 29:132-9. [DOI: 10.1080/10799890903050829] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Grimwood S, Hartig PR. Target site occupancy: Emerging generalizations from clinical and preclinical studies. Pharmacol Ther 2009; 122:281-301. [DOI: 10.1016/j.pharmthera.2009.03.002] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2009] [Accepted: 03/04/2009] [Indexed: 01/17/2023]
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KENAKIN TERRY. Functional Assays as Prismatic Views of Drug Activity: Relevance to New Drug Discovery. J Recept Signal Transduct Res 2008; 28:109-25. [DOI: 10.1080/10799890801946318] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Kenakin TP. Seven transmembrane receptors as nature's prototype allosteric protein: de-emphasizing the geography of binding. Mol Pharmacol 2008; 74:541-3. [PMID: 18583453 DOI: 10.1124/mol.108.050062] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The article in this issue by Redka et al. (p. 834) illustrates some interesting interactions between classified orthosteric (bind to the same recognition site as endogenous agonist) and allosteric (bind to a different site) ligands. Of particular interest are the methods used to deal with an obfuscating factor in these kinds of studies, namely the propensity of seven transmembrane receptors to form dimers and thus demonstrate allosteric effects through binding at the orthosteric site. The judicious use of kinetics to detect and quantify allosteric action also is demonstrated. The various unique properties of allosteric modulators are discussed in the context of the increasing prevalence of allosteric ligands as investigational drugs.
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Affiliation(s)
- Terry P Kenakin
- Department of Biological Reagents and Assay Development, GlaxoSmithKline Research and Development, 5 Moore Drive, Research Triangle Park, NC 27709, USA.
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Sayar K, Uğur Ö, Liu T, Hilser VJ, Onaran O. Exploring allosteric coupling in the alpha-subunit of heterotrimeric G proteins using evolutionary and ensemble-based approaches. BMC STRUCTURAL BIOLOGY 2008; 8:23. [PMID: 18454845 PMCID: PMC2422842 DOI: 10.1186/1472-6807-8-23] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/04/2007] [Accepted: 05/02/2008] [Indexed: 11/24/2022]
Abstract
BACKGROUND Allosteric coupling, which can be defined as propagation of a perturbation at one region of the protein molecule (such as ligand binding) to distant sites in the same molecule, constitutes the most general mechanism of regulation of protein function. However, unlike molecular details of ligand binding, structural elements involved in allosteric effects are difficult to diagnose. Here, we identified allosteric linkages in the alpha-subunits of heterotrimeric G proteins, which were evolved to transmit membrane receptor signals by allosteric mechanisms, by using two different approaches that utilize fundamentally different and independent information. RESULTS We analyzed: 1) correlated mutations in the family of G protein alpha-subunits, and 2) cooperativity of the native state ensemble of the Galphai1 or transducin. The combination of these approaches not only recovered already-known details such as the switch regions that change conformation upon nucleotide exchange, and those regions that are involved in receptor, effector or Gbetagamma interactions (indicating that the predictions of the analyses can be viewed with a measure of confidence), but also predicted new sites that are potentially involved in allosteric communication in the Galpha protein. A summary of the new sites found in the present analysis, which were not apparent in crystallographic data, is given along with known functional and structural information. Implications of the results are discussed. CONCLUSION A set of residues and/or structural elements that are potentially involved in allosteric communication in Galpha is presented. This information can be used as a guide to structural, spectroscopic, mutational, and theoretical studies on the allosteric network in Galpha proteins, which will provide a better understanding of G protein-mediated signal transduction.
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Affiliation(s)
- Kemal Sayar
- Ankara University Faculty of Medicine, Department of Pharmacology and Clinical Pharmacology, Sıhhiye 06100, Ankara, Turkey
- Ankara University Faculty of Medicine, and Molecular Biology and Technology Research and Development Unit, Sıhhiye 06100, Ankara, Turkey
| | - Özlem Uğur
- Ankara University Faculty of Medicine, Department of Pharmacology and Clinical Pharmacology, Sıhhiye 06100, Ankara, Turkey
| | - Tong Liu
- Department of Biochemistry and Molecular Biology, and Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, TX, 77555-1068 USA
| | - Vincent J Hilser
- Department of Biochemistry and Molecular Biology, and Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, TX, 77555-1068 USA
| | - Ongun Onaran
- Ankara University Faculty of Medicine, Department of Pharmacology and Clinical Pharmacology, Sıhhiye 06100, Ankara, Turkey
- Ankara University Faculty of Medicine, and Molecular Biology and Technology Research and Development Unit, Sıhhiye 06100, Ankara, Turkey
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Feng X, Müller T, Mizrachi D, Fanelli F, Segaloff DL. An intracellular loop (IL2) residue confers different basal constitutive activities to the human lutropin receptor and human thyrotropin receptor through structural communication between IL2 and helix 6, via helix 3. Endocrinology 2008; 149:1705-17. [PMID: 18162522 PMCID: PMC2276707 DOI: 10.1210/en.2007-1341] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The human lutropin receptor (hLHR) and human TSH receptor (hTSHR) are G protein-coupled receptors that play key roles in reproductive and thyroid physiology, respectively. We show using a quantitative assessment of cAMP production as a function of cell surface receptor expression that the hTSHR possesses greater basal constitutive activity than the hLHR. Further studies were undertaken to test the hypothesis that different potential Gs-coupling motifs identified in IL2 of the hTSHR and hLHR contribute to their different basal constitutive activities. Although mutating the receptors to interchange their potential Gs-coupling motifs reversed their relative activities, we show this to be due to the swapping of one IL2 residue (Q476 in the hLHR; R531 in the hTSHR). Molecular dynamics simulations show that the effect of the hLHR(Q476R) mutation, switching the structural features of the hLHR toward those of the hTSHR, is greater than the switching effect of the hTSHR(R531Q) mutant toward the hLHR. The structural model of the hLHR(Q476R) mutant can be considered as a hybrid of wild-type (wt) hTSHR and constitutively active mutant hLHR forms. In this hLHR(Q476R) mutant, IL2 adopts a structure similar to IL2 of the wt hTSHR, but it shares with the hLHR constitutively active mutant the solvent exposure and the reciprocal arrangement of helices 3, 5, and 6, including the weakening of the wt native R3.50-D6.30 interaction. Our results suggest a H3-mediated structural connection between IL2 and the cytosolic extension of H6. Thus, IL2 contributes significantly to the inactive and active state ensembles of these G protein-coupled receptors.
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Affiliation(s)
- Xiuyan Feng
- Department of Molecular Physiology and Biophysics, The Roy J. and Lucille R. Carver College of Medicine, The University of Iowa, Iowa City, IA 52242, USA
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Desjardins SF, Berchiche YA, Haddad E, Heveker N. [Multiple talents of the chemokine receptor-CXCR4]. Med Sci (Paris) 2008; 23:980-4. [PMID: 18021711 DOI: 10.1051/medsci/20072311980] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
CXCR4 is a clinically relevant chemokine receptor that has first gained attention as one of the cofactors for HIV entry into target cells. Moreover, the receptor is involved in cancer cell migration to distant metastatic sites and immune effector recruitment in inflammatory diseases such as asthma and rheumatoid arthritis. Unfortunately, pharmacologic intervention is complicated by the vital function of CXCR4 in the organism. The most prominent of these functions is its role in stem cell homing. The CXCR4 chemokine ligand, produced by bone marrow stromal cells, leads both to migration of hematopoietic stem cells towards this niche and their retention in this compartment. As models of G-protein coupled receptor (GPCR) activation evolve, it becomes clear that multiple factors modulate the functional outcome of ligand binding to a receptor. Modulation of GPCR activity, for example by allosteric ligands, may permit more subtle therapeutic approaches adapted to long term treatment. In addition, GPCR signalling can be altered by hetero-oligomerization of GPCRs. In this perspective, it might be possible to achieve modulation of GPCR signalling by also targeting the oligomerization partner of a given receptor. This approach is described using the example of strategies that aim at the optimization of stem cell homing in the context of cord blood-derived hematopoietic stem cell transplantation.
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Affiliation(s)
- Sonia F Desjardins
- Département de Biochimie, Université de Montréal, Montréal (Québec), H3T 1J4 Canada
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Abstract
Drugs are named for their primary receptor target and overt action (agonism, antagonism) but the observation of multiple or collateral efficacies emanating from drugs activating a single receptor target is posing a challenge for drug classification and nomenclature. With increasing abilities to detect alteration in cellular function has come the identification of efficacies that are not necessarily manifest in obvious changes in cell response. Specifically, some agonists selectively activate cellular pathways, demonstrate phenotypic behaviour associated with cell type and some antagonists actively induce receptor internalization without activation. In addition, the effects of allosteric modulators can be linked to the nature of the co-binding ligand posing a similar complication in classification and naming. Thus, accurate labels for this new generation of selective drugs may require identification of receptor partners (G-protein type, beta-arrestin) or pathway or, in the case of allosteric modulators, identification of co-binding ligands. The association of distinct phenotypic behaviours with molecules opens the opportunity to better associate clinical effects with distinct pharmacological properties.
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Affiliation(s)
- T P Kenakin
- Biochemical and Cellular Targets, GlaxoSmithKline Research and Development, Research Triangle Park, NC 27709, USA.
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Berchiche YA, Chow KY, Lagane B, Leduc M, Percherancier Y, Fujii N, Tamamura H, Bachelerie F, Heveker N. Direct Assessment of CXCR4 Mutant Conformations Reveals Complex Link between Receptor Structure and Gαi Activation. J Biol Chem 2007; 282:5111-5. [PMID: 17197449 DOI: 10.1074/jbc.c600270200] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ligand binding to G protein-coupled receptors (GPCRs) is thought to induce changes in receptor conformation that translate into activation of downstream effectors. The link between receptor conformation and activity is still insufficiently understood, as current models of GPCR activation fail to take an increasing amount of experimental data into account. To elucidate structure-function relationships in GPCR activation, we used bioluminescence resonance energy transfer to directly assess the conformation of mutants of the chemokine receptor CXCR4. We analyzed substitutions in the arginine cage DRY motif and in the conserved asparagine N(3.35)119, which are pivotal molecular switches for receptor conformation and activation. G(alpha)(i) activation of the mutants was either similar to wild-type CXCR4 (D133N, Y135A, and N119D) or resulted in loss of activity (R134A and N119K). Mutant N119S was constitutively active but further activated by agonist. Bioluminescence resonance energy transfer analysis suggested no simple correlation between conformational changes in response to ligand binding and activation of G(alpha)(i) by the mutants. Different conformations of active receptors were detected (for wild-type CXCR4, D133N, and N119S), suggesting that different receptor conformations are able to trigger G(alpha)(i) activity. Several conformations were also found for inactive mutants. These data provide biophysical evidence for different receptor conformations being active with respect to a single readout. They support models of GPCR structure-activity relationships that take this conformational flexibility of active receptors into account.
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Affiliation(s)
- Yamina A Berchiche
- Department of Biochemistry, Université de Montréal, Montréal, Québec H3T 1J4, Canada
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Puett D, Li Y, DeMars G, Angelova K, Fanelli F. A functional transmembrane complex: the luteinizing hormone receptor with bound ligand and G protein. Mol Cell Endocrinol 2007; 260-262:126-36. [PMID: 17059864 PMCID: PMC1866297 DOI: 10.1016/j.mce.2006.05.009] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/23/2006] [Accepted: 05/11/2006] [Indexed: 02/08/2023]
Abstract
The luteinizing hormone receptor (LHR) is one of eight members in a cluster of the rhodopsin family of the large G protein-coupled receptor (GPCR) superfamily that contains some 800-900 genes in the human genome. LHR, along with its paralogons, follicle stimulating hormone receptor (FSHR) and thyroid stimulating hormone receptor, form one of the three classes in this cluster; the two other classes contain the relaxin-binding GPCRs and orphan GPCRs. These GPCRs are characterized by a relatively large ectodomain (ECD) containing leucine-rich-repeats (LRRs); in the class of glycoprotein hormone receptors, the LRR region is capped by N-terminal and C-terminal cysteine-rich regions. Binding of human chorionic gonadotropin (hCG) or luteinizing hormone to the LHR-ECD triggers a conformational change of the transmembrane region of the receptor facilitating binding and activation of Gs, followed by effector enzyme activation and subsequent intracellular signaling. Viewing LHR as a transmembrane anchoring protein that sequentially binds hCG and Gs to give the hCG-LHR-Gs complex, numerous interactions and conformational changes must be considered. There is, unfortunately, a paucity of structural data on LHR, but crystal structures exist for hCG, the homologous FSH-FSHR-ECD (N-terminal fragment) complex, rhodopsin (in the inactive state), an active form of Galphas (transducin), and the betagamma heterodimer. Using a combined experimental (site-directed mutagenesis followed by characterization in transfected cells) and computational (homology modeling and molecular dynamics simulations) approach, good working models are being developed for the protein-protein interaction faces and, in some cases, the ensuing conformational changes induced by complex formation. hCG binding to the LHR-ECD appears to involve several LRRs; LHR activation can be described in terms of disrupting a network of H-bonds in the cytosolic halves of helices 1-3, 6, and 7; and binding of LHR to Gs involves, in large part, intracellular loop 2 binding, presumably to Gsalpha at its C-terminus. Major gaps exist in our understanding at the molecular level of the six-polypeptide chain complex, hCG-LHR-Gs, but considerable progress has been made in the past few years.
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Affiliation(s)
- D Puett
- Department of Biochemistry & Molecular Biology, Life Sciences Building, University of Georgia, 120 Green Street, Athens, GA 30602-7229, USA.
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Kenakin T. Collateral efficacy as a pharmacological problem applied to new drug discovery. Expert Opin Drug Discov 2006; 1:635-52. [DOI: 10.1517/17460441.1.7.635] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Fanelli F, De Benedetti PG. Inactive and active states and supramolecular organization of GPCRs: insights from computational modeling. J Comput Aided Mol Des 2006; 20:449-61. [PMID: 17009093 DOI: 10.1007/s10822-006-9064-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2006] [Accepted: 08/04/2006] [Indexed: 10/24/2022]
Abstract
Herein we make an overview of the results of our computational experiments aimed at gaining insight into the molecular mechanisms of GPCR functioning either in their normal conditions or when hit by gain-of-function or loss-of-function mutations. Molecular simulations of a number of GPCRs in their wild type and mutated as well as free and ligand-bound forms were instrumental in inferring the structural features, which differentiate the mutation- and ligand-induced active from the inactive states. These features essentially reside in the interaction pattern of the E/DRY arginine and in the degree of solvent exposure of selected cytosolic domains. Indeed, the active states differ from the inactive ones in the weakening of the interactions made by the highly conserved arginine and in the increase in solvent accessibility of the cytosolic interface between helices 3 and 6. Where possible, the structural hallmarks of the active and inactive receptor states are translated into molecular descriptors useful for in silico functional screening of novel receptor mutants or ligands. Computational modeling of the supramolecular organization of GPCRs and their intracellular partners is the current challenge toward a deep understanding of their functioning mechanisms.
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Affiliation(s)
- Francesca Fanelli
- Dulbecco Telethon Institute, University of Modena and Reggio Emilia, Via Campi 183, 41100 Modena, Italy.
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Mattras H, Aliau S, Demey E, Poncet J, Borgna JL. Mass spectrometry identification of covalent attachment sites of two related estrogenic ligands on human estrogen receptor alpha. J Steroid Biochem Mol Biol 2006; 98:236-47. [PMID: 16513342 DOI: 10.1016/j.jsbmb.2005.10.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2005] [Accepted: 10/07/2005] [Indexed: 11/28/2022]
Abstract
A purified preparation of human estrogen receptor alpha (hERalpha) ligand-binding domain (LBD) involving mainly the Ser(309)Ala(569) (approximately 30%) and Ser(309)Ala(571) (approximately 63%) ER portions was used to identify the covalent attachment sites of two closely related estrogenic ER affinity labels 17alpha-bromoacetamidopropylestradiol (17BAPE(2)) and 17alpha-bromoacetamidomethylestradiol (17BAME(2)). To identify and quantify the electrophile covalent attachment sites, [(14)C]17BAPE(2)- and [(14)C]17BAME(2)-alkylated hLBD preparations were trypsinized and submitted to HPLC. In each case, two radioactive fractions were obtained. Mass spectrometry analyses of the two fractions showed signals, which closely matched the molecular masses of alkylated Cys(530)Lys(531) and Cys(417)Arg(434) hLBD tryptic peptides. The covalent attachment of the two electrophiles on hLBD was assigned to the S atoms of Cys(530) and Cys(417). However, the balance between Cys(530) and Cys(417) labeling markedly differed according to the affinity label used, with the Cys(530)/Cys(417) ratio being 2.1 for 17BAPE(2), and 20 for 17BAME(2). We attempted to interpret the covalent attachment of electrophiles by molecular modeling using the crystallographic structure of LBD bound to E(2). In agreement with the different levels of Cys(417) alkylation, the LBD model with unchanged helices could not easily account for Cys(417) labeling by 17BAME(2), whereas favorable results were obtained through 17BAPE(2) docking. Moreover, labeling at Cys(530) by the two electrophiles could not be interpreted using the LBD model. This indicates that some states of solute LBD bound to the estrogenic E(2) 17alpha-derivatives differ from the structure of crystallized LBD bound to E(2).
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Fanelli F, De Benedetti PG. Computational Modeling Approaches to Structure−Function Analysis of G Protein-Coupled Receptors. Chem Rev 2005; 105:3297-351. [PMID: 16159154 DOI: 10.1021/cr000095n] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Francesca Fanelli
- Dulbecco Telethon Institute and Department of Chemistry, University of Modena and Reggio Emilia, via Campi 183, 41100 Modena, Italy.
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Abstract
Pharmacological receptor theory is discussed with special reference to advances made during the past 25 years. Thus, the operational model has supplanted analysis of drug-receptor interaction in functional systems whereas the extended ternary complex model is used routinely to simulate quantitatively G-protein-coupled receptor (GPCR) behavior. Six new behaviors for GPCRs, centered on spontaneous production of receptor active states, ligand-selective receptor active states, oligomerization with other proteins (receptor and non-receptor) and allosteric mechanisms, have been characterized and each holds the potential for new drug discovery for therapeutic benefit.
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Affiliation(s)
- Terry Kenakin
- Assay Development Compound Profiling, GlaxoSmithKline Research and Development, 5 Moore Drive, Research Triangle Park, NC 27709, USA.
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Kenakin T. Efficacy as a Vector: the Relative Prevalence and Paucity of Inverse Agonism. Mol Pharmacol 2004; 65:2-11. [PMID: 14722230 DOI: 10.1124/mol.65.1.2] [Citation(s) in RCA: 179] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
This article describes the expected phenotypic behavior of all types of ligands in constitutively active receptor systems and, in particular, the molecular mechanisms of inverse agonism. The possible physiological relevance of inverse agonism also is discussed. Competitive antagonists with the molecular property of negative efficacy demonstrate inverse agonism in constitutively active receptor systems. This is a phenotypic behavior that can only be observed in the appropriate assay; a lack of observed inverse agonism is evidence that the ligand does not possess negative efficacy only if it can be shown that constitutive receptor activity is present. In the absence of constitutive activity, inverse agonists behave as simple competitive antagonists. A survey of 105 articles on the activity of 380 antagonists on 73 biological G-protein-coupled receptor targets indicates that, in this sample dataset, 322 are inverse agonists and 58 (15%) are neutral antagonists. The predominance of inverse agonism agrees with theoretical predictions which indicate that neutral antagonists are the minority species in pharmacological space.
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Affiliation(s)
- Terry Kenakin
- Department of Assay Development and Compound Profiling, GlaxoSmithKline Research and Development, Research Triangle Park, NC 27709, USA.
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Agnati LF, Franzen O, Ferré S, Leo G, Franco R, Fuxe K. Possible role of intramembrane receptor-receptor interactions in memory and learning via formation of long-lived heteromeric complexes: focus on motor learning in the basal ganglia. JOURNAL OF NEURAL TRANSMISSION. SUPPLEMENTUM 2003:1-28. [PMID: 12946046 DOI: 10.1007/978-3-7091-0643-3_1] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/04/2023]
Abstract
Learning in neuronal networks occurs by instructions to the neurons to change their synaptic weights (i.e., efficacies). According to the present model a molecular mechanism that can contribute to change synaptic weights may be represented by multiple interactions between membrane receptors forming aggregates (receptor mosaics) via oligomerization at both pre- and post-synaptic level. These assemblies of receptors together with inter alia single receptors, adapter proteins, G-proteins and ion channels form the membrane bound part of a complex three-dimensional (3D) molecular circuit, the cytoplasmic part of which consists especially of protein kinases, protein phosphatases and phosphoproteins. It is suggested that this molecular circuit has the capability to learn and store information. Thus, engram formation will depend on the resetting of 3D molecular circuits via the formation of new receptor mosaics capable of addressing the transduction of the chemical messages impinging on the cell membrane to certain sets of G-proteins. Short-term memory occurs by a transient stabilization of the receptor mosaics producing the appropriate change in the synaptic weight. Engram consolidation (long-term memory) may involve intracellular signals that translocate to the nucleus to cause the activation of immediate early genes and subsequent formation of postulated adapter proteins which stabilize the receptor mosaics with the formation of long-lived heteromeric receptor complexes. The receptor mosaic hypothesis of the engram formation has been formulated in agreement with the Hebbian rule and gives a novel molecular basis for it by postulating that the pre-synaptic activity change in transmitter and modulator release reorganizes the receptor mosaics at post-synaptic level and subsequently at pre-synaptic level with the formation of novel 3D molecular circuits leading to a different integration of chemical signals impinging on pre- and post-synaptic membranes hence leading to a new value of the synaptic weight. Engram retrieval is brought about by the scanning of the target networks by the highly divergent arousal systems. Hence, a continuous reverberating process occurs both at the level of the neural networks as well as at the level of the 3D molecular circuits within each neuron of the network until the appropriate tuning of the synaptic weights is obtained and, subsequently, the reappearance of the engram occurs. Learning and memory in the basal ganglia is discussed in the frame of the present hypothesis. It is proposed that formation of long-term memories (consolidated receptor mosaics) in the plasma membranes of the striosomal GABA neurons may play a major role in the motivational learning of motor skills of relevance for survival. In conclusion, long-lived heteromeric receptor complexes of high order may be crucial for learning, memory and retrieval processes, where extensive reciprocal feedback loops give rise to coherent synchronized neural activity (binding) essential for a sophisticated information handling by the central nervous system.
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Affiliation(s)
- L F Agnati
- Department of BioMedical Sciences, Modena, Italy.
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