The existence of G protein-coupled glutamate receptors (also called "metabotropic" glutamate or mGlu's), belonging to the seven transmembrane spanning superfamily of receptors, was shown definitively with the cloning of the first member in 1991. Since then, eight receptors of this class have been discovered. mGlu's are members of the "Class C" subgroup of G protein-coupled receptors, distinguished by the presence of a large N-terminal domain, which contains the orthosteric agonist binding site. Based on studies with mGlu1, these receptors are proposed to exist as homodimers with the N-terminal domain forming a "clam shell" structure consisting of two lobes linked by a hinge region. Glutamate binds between these lobes to stabilize a closed state that transduces a conformational change in the transmembrane regions of the homodimer to promote G-protein coupling. The existence of C-terminal splice variants for many subtypes and intracellular interacting proteins (e.g. Homer, Pick-1) suggests that mGlu receptor function is subject to complex intracellular regulation.

The eight receptors have been classified into three groups based on similarities in their amino acid sequences, G-protein coupling and pharmacology. Group I (mGlu1 and 5) couple to Gq and signal through inositol phospholipid breakdown whereas Group II (mGlu2 and 3) and Group III (mGlu4, 6, 7 and 8) couple to Gi/o and inhibit adenylyl cyclase. In addition, members of all three groups can interact directly with voltage-gated calcium or potassium channels though their G proteins. Numerous pharmacological tools for these receptors exist. These include several "Group-selective" agonists, specifically: quisqualate and S-DHPG for Group I; 2R,4R-APDC and LY-354740 for Group II; as well as L-AP-4 and RS-PPG for Group III. Likewise, several "Group-selective" antagonists have been identified, specifically: LY393675 for Group I; LY341495 and MGS0039 for Group II; as well as MAP4 and UPB1110 for Group III.

Subtype-selective ligands for some of the mGlu receptors have also been described. In Group I, selective antagonists for mGlu1 include the competitive antagonist LY-367385; and the non-competitive antagonists CPCCOEt, R214127 and BAY63-7620. CHPG is a selective, but relatively low potency, agonist for mGlu5 receptors and selective non-competitive antagonists include MPEP, MTEP and DeMeOB. In Group II, the naturally occurring dipeptide NAAG is a selective agonist for mGlu3 receptors. Subtype selective agents within Group III have been less forthcoming, although (S)-homoAMPA is a weak, but selective agonist for mGlu6 receptors, and (S)-3,4-DCPG is a potent and selective agonist for mGlu8 receptors.

An exciting development in mGlu pharmacology is the discovery of allosteric modulators of several subtypes. These compounds bind in the 7-transmembrane domains to either positively or negatively modulate receptor activation by glutamate. The subtype selective "non-competitive antagonists" described above act in this way. In addition, positive allosteric modulators (which do not directly activate the receptor, but produce a leftward shift in the agonist dose-response curve) have been identified, e.g.: Ro 67-7476 and Ro 01-6128 for mGlu1, CPPHA, DFB and CDPPB for mGlu5, LY-487379 for mGlu2 and PHCCC for mGlu4. Interestingly, a "neutral" modulator for mGlu5 has also been identified (DCB), that blocks the action of positive and negative allosteric modulators at this subtype without altering the glutamate-site binding or receptor activation. From a therapeutic perspective, allosteric modulators are an attractive approach since they typically exhibit high affinity, excellent subtype selectivity, have better "drug-like" properties (e.g. blood/brain barrier penetration) than glutamate analogs acting at the transmitter recognition site, and act to either up or down regulate the actions of the glutamate at the targeted subtype in concert with neurotransmitter release.

In general, all three groups of G protein-coupled glutamate receptors are widely distributed throughout the CNS and evidence exits for postsynaptic, presynaptic and, in some cases, glial localization. One or more of the Group II and Group III receptors are believed to function as an autoreceptor, mediating of glutamate release from its nerve terminals. Presynaptic Group II and III receptors directly decrease the release of other neurotransmitters (for example dopamine and GABA) acting as hetereo-autoreceptors. In contrast, a presynaptic Group I receptor may promote glutamate release. Interestingly, a variant of mGlu4 with a truncated N-terminal domain exists on taste buds and is proposed to give rise to umami, the characteristic taste of monosodium glutamate. Activation of (presumably) postsynaptic Group I receptors potentiates NMDA receptor function. mGlu1 and mGlu5 agonists and positive allosteric modulators have been proposed as a novel approach to treat schizophrenia, whereas antagonists at these subtypes have been proposed as potential treatments for pain, drug addiction, anxiety, Parkinson'€™s disease and obesity, and also possess neuroprotective and anti-epileptic properties. Group II receptor agonists and positive allosteric modulators are effective in animal models of epilepsy, anxiety and psychosis, and LY354740 has been reported to be effective in patients with generalized anxiety. Group III agonists and positive allosteric modulators are effective in animal models of epilepsy, are neuroprotective and reverse the motor dysfunction in animal models of Parkinson's disease.

The Table below contains accepted modulators and additional information. For a list of additional products, see the "Similar Products" section below.

Footnotesa) G Protein family is also referred to as metabotropic. b) Allosteric ligands bind outside of the glutamate recognition site and either positively modulate glutamate response, act as non-competitive antagonists or neutral ligands blocking allosteric site interaction only. c) Also significant antagonism of Group I and Group III receptors. d) In cell lines expressing recombinant receptor subtypes.

Abbreviations

L-AP-4: 2-Amino-4-phosphonobutyric acid
(2R,4R)-APDC: (2R,4R)-Aminopyrrolidine-2,4-dicarboxylic acid
BAY36-7620: (3aS,6aS)-6a-Naphtalen-2-ylmethyl-5-methyliden-hexahydro-cyclopental[c]furan-1-on
z-CBQA: (Z)-1-Amino-3-[2′-(3′,5′-dioxo-1′,2′,4′-oxadiazolidinyl-cyclobutane-1-carboxylic acid
CDPPB: 3-Cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide
CHPG: (R/S)-2-Chloro-5-hydroxyphenylglycine
Compound 4: 1-(2-Hydroxy-3-propyl-4-[4-[4-(2H-tetrazol-5-yl)phenoxy]-butoxy]phenyl)ethanone – see Pinkerton, et al., J. Med. Chem., 47, 4595 (2004).
Compound 10: 2-[2-[3-(Pyridine-3-yloxy)phenyl]-2H-tetrazole-5-yl]pyridine – see Huang, et al., Bioorg. Med. Chem. Lett., 14, 5473 (2004)
CPCCOEt: 7-Cyclopropan[b]chromen-1a-carboxylic acid ethyl ester
CPPHA: N-[4-Chloro-2-[(1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)methyl]phenyl]-2-hydroxybenzamide
DCG-IV: (2S,1'R,2'R,3'R)-2-(2,3 Dicarboxycyclopropyl)glycine
DCB: 3,3′-Dichlorobenzaldazine
DFB: 3,3′-Difluorobenzaldazine
DMeOB: 3,3′-Dimethoxybenzaldazine
S-DHPG: (R,S)-3,5-Dihydroxyphenylglycine
S-3,4-DCPG: (S)-3,4-Dicarboxyphenylglycine
E-GLU: (S)-α-Ethylglutamic acid
S-Homo-AMPA: (RS)-2-Amino-4-(3-hydroxy-5-methylisoxazol-4-yl)butyric acid
LY341495: (2S)-2-Amino-2-(1S,2S-2-carboxycyclopronan-1-yl-3-(xanth-9-yl)propanoic acid
LY354740: (+)-2-Aminobicyclo[3.1.0]hexane-2,6-dicarboxylic acid
LY367385: (+)-2-Methyl-4-carboxyphenylglycine
LY379268: (–)-2-Thia-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate
LY487379: 2,2,2-Trifluoro-N-[4-(2-methoxyphenoxy)phenyl]-N-(3-pyridinylmethyl)-ethanesulfonamide
MAP4: (S)-2-Amino-2-methyl-4-phosphonobutyric acid
MGS 0039: (1R,2R,3R,5R,6R)-2-Amino-3-(3,4-dichlorobenzyloxy)-6-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid
MPEP: 2-Methyl-6-(phenylethynyl)pyridine
MTEP: 3-[(2-Methyl-1,3-thiazol-4-yl)ethynyl]pyridine
NAAG: N-Acetyl-L-aspartyl-l-glutamic acid
PHCCC: N-Phenyl-7-(hydroxylimino)cyclopropa[b]-chromen-1a-carboxamide
Ro 01-6128: Diphenylacetyl-carbamic acid ethyl ester
Ro 67-7476: (S)-2-(4-Fluoro-phenyl)-1-(toluene-4-sulfonyl)-pyrrolidine
R214127: 1-(3,4-Dihydro-2H-pyrano[2,3-b]quinolin-7-yl)-2-phenyl-1-ethanone
RS-PPG: (RS)-4-Phosphonophenylglycine
SIB-1757: 6-Methyl-2-(phenylazo)-pyridinol
SIB-1893: (E)-2-Methyl-6-(2-phenylethenyl)pyridine
L-SOP: L-Serine-O-phosphate
UBP1110: (RS)-α-Methyl-3-chloro-4-phosphonophenylglycine

Similar Products
Loading

References

1.
Bradley SJ, Challiss RJ. 2012. G protein-coupled receptor signalling in astrocytes in health and disease: A focus on metabotropic glutamate receptors. Biochemical Pharmacology. 84(3):249-259. http://dx.doi.org/10.1016/j.bcp.2012.04.009
2.
Bräuner-Osborne H, Egebjerg J, Nielsen, Madsen U, Krogsgaard-Larsen P. 2000. Ligands for Glutamate Receptors:  Design and Therapeutic Prospects. J. Med. Chem.. 43(14):2609-2645. http://dx.doi.org/10.1021/jm000007r
3.
Cartmell J, Schoepp DD. Regulation of Neurotransmitter Release by Metabotropic Glutamate Receptors. 75(3):889-907. http://dx.doi.org/10.1046/j.1471-4159.2000.0750889.x
4.
Chaudhari N, Landin AM, Roper SD. 2000. A metabotropic glutamate receptor variant functions as a taste receptor. Nat Neurosci. 3(2):113-119. http://dx.doi.org/10.1038/72053
5.
CONN PJ. 2003. Physiological Roles and Therapeutic Potential of Metabotropic Glutamate Receptors. 1003(1):12-21. http://dx.doi.org/10.1196/annals.1300.002
6.
Fagni L. 2012. Diversity of Metabotropic Glutamate Receptor?Interacting Proteins and Pathophysiological Functions.63-79. http://dx.doi.org/10.1007/978-3-7091-0932-8_3
7.
Fagni L, Worley PF, Ango F. 2002. Homer as Both a Scaffold and Transduction Molecule. Science Signaling. 2002(137):re8-re8. http://dx.doi.org/10.1126/stke.2002.137.re8
8.
Gasparini F. 2002. Allosteric modulators of group I metabotropic glutamate receptors: novel subtype-selective ligands and therapeutic perspectives. 2(1):43-49. http://dx.doi.org/10.1016/s1471-4892(01)00119-9
9.
Goudet C, Gaven F, Kniazeff J, Vol C, Liu J, Cohen-Gonsaud M, Acher F, Prezeau L, Pin JP. 2004. Heptahelical domain of metabotropic glutamate receptor 5 behaves like rhodopsin-like receptors. Proceedings of the National Academy of Sciences. 101(1):378-383. http://dx.doi.org/10.1073/pnas.0304699101
10.
Jensen AA, Greenwood JR, Bräuner-Osborne H. 2002. The dance of the clams: twists and turns in the family C GPCR homodimer. Trends in Pharmacological Sciences. 23(11):491-493. http://dx.doi.org/10.1016/s0165-6147(02)02107-7
11.
Julio-Pieper M, Flor PJ, Dinan TG, Cryan JF. 2011. Exciting Times beyond the Brain: Metabotropic Glutamate Receptors in Peripheral and Non-Neural Tissues. Pharmacol Rev. 63(1):35-58. http://dx.doi.org/10.1124/pr.110.004036
12.
Kunishima N, Shimada Y, Tsuji Y, Sato T, Yamamoto M, Kumasaka T, Nakanishi S, Jingami H, Morikawa K. 2000. Structural basis of glutamate recognition by a dimeric metabotropic glutamate receptor. Nature. 407(6807):971-977. http://dx.doi.org/10.1038/35039564
13.
Marino MJ, Williams DL, O'Brien JA, Valenti O, McDonald TP, Clements MK, Wang R, DiLella AG, Hess JF, Kinney GG, et al. 2003. Allosteric modulation of group III metabotropic glutamate receptor 4: A potential approach to Parkinson's disease treatment. Proceedings of the National Academy of Sciences. 100(23):13668-13673. http://dx.doi.org/10.1073/pnas.1835724100
14.
C. Montana M, W. Gereau R. 2011. Metabotropic Glutamate Receptors as Targets for Analgesia: Antagonism, Activation, and Allosteric Modulation. CPB. 12(10):1681-1688. http://dx.doi.org/10.2174/138920111798357438
15.
Pin J, Acher F. 2002. The Metabotropic Glutamate Receptors: Structure, Activation Mechanism and Pharmacology. CDTCNSND. 1(3):297-317. http://dx.doi.org/10.2174/1568007023339328
16.
Schoepp DD, Jane DE, Monn JA. 1999. Pharmacological agents acting at subtypes of metabotropic glutamate receptors. Neuropharmacology. 38(10):1431-1476. http://dx.doi.org/10.1016/s0028-3908(99)00092-1
17.
Sheffler DJ, Gregory KJ, Rook JM, Conn PJ. 2011. Allosteric Modulation of Metabotropic Glutamate Receptors.37-77. http://dx.doi.org/10.1016/b978-0-12-385952-5.00010-5
18.
Volpi C, Fazio F, Fallarino F. 2012. Targeting metabotropic glutamate receptors in neuroimmune communication. Neuropharmacology. 63(4):501-506. http://dx.doi.org/10.1016/j.neuropharm.2012.05.024

Social Media

LinkedIn icon
Twitter icon
Facebook Icon
Instagram Icon

MilliporeSigma

Research. Development. Production.

We are a leading supplier to the global Life Science industry with solutions and services for research, biotechnology development and production, and pharmaceutical drug therapy development and production.

© 2021 Merck KGaA, Darmstadt, Germany and/or its affiliates. All Rights Reserved.

Reproduction of any materials from the site is strictly forbidden without permission.