Mechanistic hypotheses for the activation of G-protein-coupled receptors

doi:10.1016/0898-6568(95)02057-8

Cellular Signalling

Volume 8, Issue 3, March 1996, Pages 217-224

https://doi.org/10.1016/0898-6568(95)02057-8 Get rights and content

Abstract

G-protein-coupled receptors (GPCR) play an important role in the functioning of the nervous and endocrine systems. Intensive efforts devoted to mutational analyses of GPCR have greatly enhanced our understanding of the receptor-G-protein signalling pathway. Nonetheless, the lack of receptor structural data mandates that the mechanism of receptor activation can only be probed indirectly through hypothesis testing. Mechanistic models at two different levels, a thermodynamic model and a structural model, are reviewed here. A general thermodynamic model can be used as a framework for analyzing macroscopic experimental data, while a probability function based on a helical-rotation model can potentially provide a link between microscopic conformational changes and macroscopic rate constants and equilibrium constants. Conformational induction and conformational selection are two inseparable consequences of the receptor-binding system. Mechanistic models based on the integration of mutational data, spectroscopic data, and model simulation will form a foundation upon which further experiments can be designed, and consideration of both thermodynamic and structural principles will provide coherent insights into the receptor-activation process.

References (74)

V.M. Unger et al.
Biophys. J.
(1995)
B.R. Conklin et al.
Cell
(1993)
D. Mackay
J. Theor. Biol.
(1990)
A. Gero
J. Theor. Biol.
(1983)
M.B. Jackson
Trends Biochem. Sci.
(1994)
R.J. Lefkowitz et al.
Trends Pharmacol. Sci.
(1993)
M.J. Robertson et al.
Trends Pharmacol. Sci.
(1994)
G. Milligan et al.
Trends Pharmacol. Sci.
(1995)
P. Leff
Trends Pharmacol. Sci.
(1995)
M.A. Kjelsberg et al.
J. Biol. Chem.
(1992)

S.C. Sealfon et al.

J. Biol. Chem.

(1995)

J.A. Ballesteros et al.

J. Findlay et al.

Trends Pharmacol. Sci.

(1990)

M.F. Hibert et al.

Trends Pharmacol. Sci.

(1993)

T.M. Fong et al.

J. Biol. Chem.

(1994)

M. Wessling-Resnick et al.

Trends Biochem. Sci.

(1987)

P.A. Mahama et al.

Biophys. J.

(1994)

K.E. Hedin et al.

Cell. Signal.

(1993)

G.S. Roth et al.

Trends Neurosci.

(1995)

L. Needham et al.

Biochim. Biophys. Acta

(1987)

D.J. Underwood et al.

Chem. Biol.

(1994)

M. Rodbell

Nature

(1980)

Cited by (24)

Conformational state of human cardiac 5-HT<inf>4(g)</inf> receptors influences the functional effects of polyclonal anti-5-HT<inf>4</inf> receptor antibodies
2007, Biochemical Pharmacology
Citation Excerpt :
In this line of CHO cells expressing the h5-HT4(g) receptor, the basal cAMP level in the absence of an agonist was about 1.4-fold greater than in untransfected CHO cells. It therefore seems that h5-HT4(g) receptors showed a constitutive activity in the absence of any 5-HT4 ligand and that a fraction of these receptors is under a spontaneously active state (R*) in the membrane [31]. The ability of these cells to produce intracellular cAMP via direct activation of the adenylate cyclase was determined with 10 μM forskolin.
The functional effects of the anti-G21V antibody directed against the second extracellular loop of human heart 5-HT₄ receptors can differ when the receptors are expressed in different cell lines. Here, we extend these studies to show variation in the responses of 5-HT_4(g) receptors to the antibody within the same expression system. In a previous report no effect of the anti-G21V antibodies had been shown upon 5-HT_4(g) receptors expressed in CHO cells. Here the same antibodies alone or when added before 5-HT had a functional “inverse-agonist like” effect upon 5-HT_4(g) receptors expressed in a separate line of CHO cells. Although these CHO cells showed a lower efficacy of cAMP production evoked by 5-HT than the previous report they express a similar h5-HT_4(g) receptor density. Inhibition of either phosphodiesterases or Gi proteins had no effect upon the action of the antibody. Conformational states of the 5-HT₄ receptor and/or equilibrium between different states of receptors may then determine the functional effect of antibodies against this receptor.
G protein-coupled receptor signalling and cross-talk: Achieving rapidity and specificity
2002, Cellular Signalling
Activation of a given type of G protein-coupled receptor (GPCR) triggers a limited set of signalling events in a very rapid and specific manner. The classical paradigm of GPCR signalling was rather linear and sequential. Emerging evidence, however, has revealed that this is only a part of the complex signalling mediated by GPCR. Propagation of GPCR signalling involves cross-regulation of many but specific pathways, including cross-talks between different GPCRs as well as with other signalling pathways. Moreover, it is increasingly apparent that GPCRs can activate both heterotrimeric G protein-dependent and G protein-independent signalling pathways. In this review, we discuss how the signallings initiated by GPCRs achieve rapidity as well as specificity, and how the GPCRs can cross-regulate other specific signalling pathways at the same time. New concepts regarding GPCR signalling have been arising to address this issue, which include multiprotein signalling complex and signalling compartment in microdomain concepts that enable close colocalization or even contact among the proteins engaged in the specific signal transduction. The final outcome of a stimulation of GPCR will thus be the sum of its own specific set of intracellular signalling pathways it regulates.
Length analyses of mammalian G-protein-coupled receptors
2001, Journal of Theoretical Biology
G-protein-coupled receptors (GPCRs) play a crucial role in mediating effects of extracellular messengers in a wide variety of biological systems, comprising the largest gene superfamily at least in mammals. Mammalian GPCRs are broadly classified into three families based on pharmacological properties and sequence similarities. These sequence similarities are largely confined to the seven transmembrane domains, and much less in the extracellular and intracellular loops and terminals (LTs). Together with the fact that the LTs vary considerably in length and sequence, the LT length of GPCRs has not been studied systematically. Here we have applied a statistical analysis to the length of the LTs of a wide variety of mammalian GPCRs in order to examine the existence of any trends in molecular architecture among a known mammalian GPCR population. Tree diagrams constructed by cluster analyses, using eight length factors in a given GPCR, revealed possible length relations among GPCRs and defined at least three groups. Most samples in Group J (joined) and Group M (minor) had an exceptionally long N-terminal and I3 loop, respectively; and other samples were considered as Group O (other/original). This length-based classification largely coincided with the conventional sequence- and pharmacology-based classification, suggesting that the LT length contains some biological information when analysed at the population level. Principle component analyses suggested the existence of inherent length differences between loops and terminals as well as between extracellular and intracellular LTs. Wilcoxon rank transformation tests unveiled statistically significant differences between Group O and Group J, not only in the N-terminal and I3 loop, but also in the E3 loop. Correlation analyses identified an E1-I2 length-correlation in Group O and Group J and an N-E3 length-correlation in Group J. Taken together, these results suggest a possible functional importance of LT length in the GPCR superfamily.
D<inf>2</inf> dopamine receptor-G protein coupling. Cross-regulation of agonist and guanosine nucleotide binding sites
2001, Neuroscience Letters
The cross regulation of agonist binding to D₂ dopamine receptors and guanosine nucleotide binding to G proteins was studied using membranes of Chinese hamster ovary cells expressing rat D_2short dopamine receptors. All guanosine nucleotides studied caused a concentration-dependent loss of high-affinity agonist binding sites of D₂ receptors with potencies corresponding to their affinity to bind to G proteins in these membranes. On the other hand, the dopaminergic agonists, but not antagonists, decreased the affinities of guanosine diphosphate and guanosine monophosphate, but not of guanosine 5′-(γ-thiotriphosphate). The cross regulation of ligand binding to D₂ dopamine receptors and G proteins suggests the existence of several conformational states of these proteins during the signal transduction and that the high-affinity state of agonist binding is a transient state of the agonist-receptor-G protein complex, where no nucleotides are bound.
Switching agonist/antagonist properties of opiate alkaloids at the δ opioid receptor using mutations based on the structure of the orphanin FQ receptor
2000, Journal of Biological Chemistry
In an earlier study, we have demonstrated that by mutating five amino acid residues to those conserved in the opioid receptors, the OFQ receptor could be converted to a functional receptor that bound many opioid alkaloids with nanomolar affinities. Surprisingly, when the reciprocal mutations, Lys-214 → Ala (TM5), Ile-277 → Val/His-278 → Gln/Ile-279 → Val (TM6), and Ile-304 → Thr (TM7), are introduced in the δ receptor, neither the individual mutations nor their various combinations significantly reduce the binding affinities of opioid alkaloids tested. However, these mutations cause profound alterations in the functional characteristics of the mutant receptors as measured in guanosine 5′-3-O-(thio)triphosphate binding assays. Some agonists become antagonists at some constructs as they lose their ability to activate them. Some alkaloid antagonists are transformed into agonists at other constructs, but their agonistic effects can still be blocked by the peptide antagonist TIPP. Even the δ inverse agonist 7-benzylidenenaltrexone becomes an agonist at the mutant containing both the Ile-277 → Val/His-278 → Gln/Ile-279 → Val and Ile-304 → Thr mutations. Thus, although the mutated residues are thought to be part of the binding pocket, they are critically involved in the control of the δ receptor activation process. These findings shed light on some of the structural bases of ligand efficacy. They are also compatible with the hypothesis that a ligand may achieve high affinity binding in several different ways, each having different effects on receptor activation.
Modelling G-protein-coupled receptors for drug design
1999, Biochimica et Biophysica Acta - Reviews on Biomembranes
The G-protein coupled receptors form a large and diverse multi-gene superfamily with many important physiological functions. As such, they have become important targets in pharmaceutical research. Molecular modelling and site-directed mutagenesis have played an important role in our increasing understanding of the structural basis of drug action at these receptors. Aspects of this understanding, how these techniques can be used within a drug-design programme, and remaining challenges for the future are reviewed.

View all citing articles on Scopus

View full text

Mechanistic hypotheses for the activation of G-protein-coupled receptors

Abstract

Biophys. J.

Cell

J. Theor. Biol.

J. Theor. Biol.

Trends Biochem. Sci.

Trends Pharmacol. Sci.

Trends Pharmacol. Sci.

Trends Pharmacol. Sci.

Trends Pharmacol. Sci.

J. Biol. Chem.

J. Biol. Chem.

Curr. Opin. Biotechnol.

J. Pharmacol. Toxicol. Methods

Trends Pharmacol. Sci.

J. Biol. Chem.

J. Biol. Chem.

J. Biol. Chem.

J. Biol. Chem.

J. Biol. Chem.

Trends Pharmacol. Sci.

J. Biol. Chem.

J. Biol. Chem.

Eur. J. Pharmacol.

J. Biol. Chem.

J. Biol. Chem.

J. Biol. Chem.

Trends Pharmacol. Sci.

Trends Pharmacol. Sci.

J. Biol. Chem.

Trends Biochem. Sci.

Biophys. J.

Cell. Signal.

Trends Neurosci.

Biochim. Biophys. Acta

Chem. Biol.

Nature