Identification of a novel transmembrane domain involved in the negative modulation of mGluR1 using a newly discovered allosteric mGluR1 antagonist, 3-cyclohexyl-5-fluoro-6-methyl-7-(2-morpholin-4-ylethoxy)-4H-chromen-4-one.
Currently tested allosteric modulators for metabotropic glutamate receptor 1 (mGluR1) are known to regulate the activity of mGluR1 mainly through transmembrane (TM) domain 6 and/or 7. We identified a novel interaction site, N760 in TM5, which negatively regulates activation of mGluR1 with a newly discovered selective mGluR1 antagonist, 3-cyclohexyl-5-fluoro-6-methyl-7-(2-morpholin-4-ylethoxy)-4H-chromen-4-one (CFMMC). CFMMC inhibited L-glutamate-induced intracellular Ca(2+) mobilization ([Ca(2+)]i) in Chinese hamster ovary (CHO) cells expressing recombinant human mGluR1a with IC(50) value of 50 nM, whereas it did not inhibit [Ca(2+)]i in CHO cells expressing human mGluR5a (IC(50); >10 microM). To identify the amino acid residues critical for antagonism of CFMMC, we constructed various point mutants of human mGluR1 and evaluated them in [Ca(2+)]i assays. The inhibitory effects of CFMMC were significantly affected in point mutations of either I725 in TM4 or N760 in TM5, as well as mutations of W798, F801 and Y805 in TM6 or T815 in TM7. Further studies revealed that antagonistic activities of not only CFMMC but also other, structurally unrelated, mGluR1 antagonists such as 6-amino-N-cyclohexyl-N,3-dimethylthiazolo[3,2-a]benzimidazole-2-carboxamide (YM-298198) and Compound 1 were reduced in N760 mutated mGluR1a. These results indicate that some mGluR1 allosteric antagonists require N760 in TM5 to demonstrate negative modulation of mGluR1 in addition to the reported amino acid residues in TM6 and TM7.
Fukuda
Junko
J
Tsukuba Research Institute Banyu Pharmaceutical Co, Ltd, Tsukuba, Ibaraki 300-2611, Japan. dbhyb957@yahoo.co.jp
Suzuki
Gentaroh
G
Kimura
Toshifumi
T
Nagatomi
Yasushi
Y
Ito
Satoru
S
Kawamoto
Hiroshi
H
Ozaki
Satoshi
S
Ohta
Hisashi
H
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D002867:Chromones / Q000008:administration & dosage / Q000737:chemistry / Q000494:pharmacology*; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D018014:Gene Transfer Techniques; D018698:Glutamic Acid / Q000378:metabolism; D006801:Humans; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D008969:Molecular Sequence Data; D009025:Morpholines / Q000008:administration & dosage / Q000737:chemistry / Q000494:pharmacology*; D017354:Point Mutation; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000235:genetics; D017386:Sequence Homology, Amino Acid
C544944:3-cyclohexyl-5-fluoro-6-methyl-7-(2-morpholin-4-ylethoxy)-4H-chromen-4-one; D002867:Chromones; C578935:GRM5 protein, human; D009025:Morpholines; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; D011994:Recombinant Proteins; C108822:metabotropic glutamate receptor 2; C104077:metabotropic glutamate receptor type 1; D018698:Glutamic Acid; D002118:Calcium