Extreme C terminus of G protein alpha-subunits contains a site that discriminates between Gi-coupled metabotropic glutamate receptors.
Metabotropic glutamate receptors (mGlu receptors), the Ca2+-sensing receptor, gamma-aminobutyric acid type B receptors, and one group of pheromone receptors constitute a unique family (also called family 3) of heptahelical receptors. This original family shares no sequence similarity with any other G protein-coupled receptors. The identification and comparison of the molecular determinants of receptor/G protein coupling within the different receptor families may help identify general rules involved in this protein/protein interaction. In order to detect possible contact sites important for coupling selectivity between family 3 receptors and the G protein alpha-subunits, we examined the coupling of the cyclase-inhibiting mGlu2 and mGlu4 receptors to chimeric alphaq-subunits bearing the 5 extreme C-terminal amino acid residues of either Galphai, Galphao, or Galphaz. Whereas mGlu4 receptor activated all three chimeric G proteins, mGlu2 receptor activated Galphaqi and Galphaqo but not Galphaqz. The mutation of isoleucine -4 of Galphaqz into cysteine was sufficient to recover coupling of the mutant G protein to mGlu2 receptor. Moreover, the mutation of cysteine -4 of Galphaqo into isoleucine was sufficient to suppress the coupling to mGlu2 receptor. Mutations at positions -5 and -1 had an effect on coupling efficiency, but not selectivity. Our results emphasize the importance of the residue -4 of the alpha-subunits in their specific interaction to heptahelical receptors by extending this finding on the third family of G protein-coupled receptors.
Blahos
J
J
Mécanismes Moléculaires des Communications Cellulaires, CNRS-UPR9023, CCIPE, F-34094 Montpellier Cedex 5, France.
Mary
S
S
Perroy
J
J
de Colle
C
C
Brabet
I
I
Bockaert
J
J
Pin
J P
JP
D002460:Cell Line; D000939:Epitopes; D019204:GTP-Binding Proteins / Q000737:chemistry* / Q000235:genetics; D018698:Glutamic Acid / Q000494:pharmacology; D006388:Hemagglutinins / Q000235:genetics; D007295:Inositol Phosphates / Q000378:metabolism; D016297:Mutagenesis, Site-Directed / Q000235:genetics; D017354:Point Mutation / Q000235:genetics; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism*; D016415:Sequence Alignment
D000939:Epitopes; D006388:Hemagglutinins; D007295:Inositol Phosphates; D018094:Receptors, Metabotropic Glutamate; C108822:metabotropic glutamate receptor 2; D018698:Glutamic Acid; D019204:GTP-Binding Proteins; C108823:metabotropic glutamate receptor 4