The agonist selectivity of a class III metabotropic glutamate receptor, human mGluR4a, is determined by the N-terminal extracellular domain.
To test the hypothesis that the determinants for agonist selectivity of class III metabotropic glutamate receptors (mGluRs) are localized in the N-terminal extracellular domain, a chimaeric cDNA was constructed where 519 amino acids of the N-terminal extracellular domain of human mGluR1b were exchanged with the corresponding region of human mGluR4. The pharmacological profile of the chimaera, designated hmGlu(R4)1-519/1b, was analysed by recordings of intracellular calcium concentration ([Ca2+]i) in transiently transfected HEK 293 cells and compared with that of human mGluR1b and human mGluR4a stably expressed in Chinese hamster ovary cells. Application of 100 microM L-2-amino-4-phosphonobutyrate (L-AP4), a class III mGluR-specific agonist, induced a rise in [Ca2+]i in hmGlu(R4)1-519/1b but not in hmGluR1b expressing cells. In contrast, application of quisqualate (100 microM) induced a rise in [Ca2+]i at hmGluR1b but not at hmGlu(R4)1-519/1b. Dose-response analysis with L-AP4 and L-glutamate at hmGlu(R4)1-519/1b revealed a half-maximal effect (EC50) of 16.0 microM and 196 microM, respectively. The EC50 values for quisqualate, glutamate and (1S,3R)-ACPD at hmGluR1b were 10.25 microM, 225 microM and 3060 microM, respectively. The rank order of agonist potency of hmGlu(R4)1-519/1b corresponds to that of hmGluR4 (L-AP4 > L-glutamate > (1S,3R)-ACPD > quisqualate) but is different from that of hmGluR1b (quisqualate > glutamate >> (1S,3R)-ACPD).
Tones
M A
MA
Department of Cellular and Molecular Biology, CNS Research, Basle, Switzerland.
Bendali
N
N
Flor
P J
PJ
Knöpfel
T
T
Kuhn
R
R
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D006224:Cricetinae; D006801:Humans; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D018094:Receptors, Metabotropic Glutamate / Q000819:agonists* / Q000096:biosynthesis / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000819:agonists / Q000096:biosynthesis
D018094:Receptors, Metabotropic Glutamate; D011993:Recombinant Fusion Proteins