Extreme C Terminus of G Protein α-Subunits Contains a Site That Discriminates between Gi-coupled Metabotropic Glutamate Receptors (original) (raw)
Related papers
Journal of Biological Chemistry, 1998
Metabotropic glutamate receptors (mGlu receptors), the Ca 2؉ -sensing receptor, ␥-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 ␣-subunits, we examined the coupling of the cyclase-inhibiting mGlu2 and mGlu4 receptors to chimeric ␣ q -subunits bearing the 5 extreme C-terminal amino acid residues of either G␣ i , G␣ o , or G␣ z . Whereas mGlu4 receptor activated all three chimeric G proteins, mGlu2 receptor activated G␣ qi and G␣ qo but not G␣ qz . The mutation of isoleucine ؊4 of G␣ qz into cysteine was sufficient to recover coupling of the mutant G protein to mGlu2 receptor. Moreover, the mutation of cysteine ؊4 of G␣ qo 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 ␣-subunits in their specific interaction to heptahelical receptors by extending this finding on the third family of G protein-coupled receptors.
A Novel Site on the Gα-protein That Recognizes Heptahelical Receptors
Journal of Biological Chemistry, 2001
Specific domains of the G-protein ␣ subunit have been shown to control coupling to heptahelical receptors. The extreme N and C termini and a region between ␣4 and ␣5 helices of the G-protein ␣ subunit are known to determine selective interaction with the receptors. The metabotropic glutamate receptor 2 activated both mouse G␣ 15 and its human homologue G␣ 16 , whereas metabotropic glutamate receptor 8 activated G␣ 15 only. The extreme C-terminal 20 amino acid residues are identical between the G␣ 15 and G␣ 16 and are therefore unlikely to be involved in coupling selectivity. Our data reveal two regions on G␣ 16 that inhibit its coupling to metabotropic glutamate receptor 8. On a three-dimensional model, both regions are found in a close proximity to the extreme C terminus of G␣ 16. One module comprises ␣4 helix, ␣4؊6 loop (L9 Loop), 6 sheet, and ␣5 helix. The other, not described previously, is located within the loop that links the N-terminal ␣ helix to the 1 strand of the Ras-like domain of the ␣ subunit. Coupling of G␣ 16 protein to the metabotropic glutamate receptor 8 is partially modulated by each module alone, whereas both modules are needed to eliminate the coupling fully.
A Novel Site on the Galpha -protein That Recognizes Heptahelical Receptors
Journal of Biological Chemistry, 2001
Specific domains of the G-protein ␣ subunit have been shown to control coupling to heptahelical receptors. The extreme N and C termini and a region between ␣4 and ␣5 helices of the G-protein ␣ subunit are known to determine selective interaction with the receptors. The metabotropic glutamate receptor 2 activated both mouse G␣ 15 and its human homologue G␣ 16 , whereas metabotropic glutamate receptor 8 activated G␣ 15 only. The extreme C-terminal 20 amino acid residues are identical between the G␣ 15 and G␣ 16 and are therefore unlikely to be involved in coupling selectivity. Our data reveal two regions on G␣ 16 that inhibit its coupling to metabotropic glutamate receptor 8. On a three-dimensional model, both regions are found in a close proximity to the extreme C terminus of G␣ 16 . One module comprises ␣4 helix, ␣4؊6 loop (L9 Loop), 6 sheet, and ␣5 helix. The other, not described previously, is located within the loop that links the N-terminal ␣ helix to the 1 strand of the Ras-like domain of the ␣ subunit. Coupling of G␣ 16 protein to the metabotropic glutamate receptor 8 is partially modulated by each module alone, whereas both modules are needed to eliminate the coupling fully.
Molecular Pharmacology, 1998
Metabotropic glutamate (mGlu), Ca 2ϩ-sensing, ␥-aminobutyric acid B , and a large number of pheromone receptors constitute a peculiar family of G protein-coupled receptors. They possess a large extracellular domain that has been proposed to constitute their ligand binding domain. The aim of the current study was to examine whether this large ligand binding domain had any influence on the G protein-coupling selectivity of the receptor, and vice versa. We chose mGlu receptors, which are classified into three groups according to their sequence homology and pharmacology, as representatives of this receptor family. To define a G protein-coupling profile for these receptors, we used a set of exogenous phospholipase C-activating G proteins in the same way that synthetic ligands are used to define agonist and antagonist pharmacological profiles. This set includes G ␣15 , G ␣16 , G ␣q , and chimeric G ␣q proteins with the last few amino acids of either G ␣i2 (G ␣qi), G ␣o (G ␣qo), or G ␣z (G ␣qz). Cotransfection of mGlu receptors with these G proteins and examination of their coupling to phospholipase C revealed that group I, II, and III receptors have distinct G protein-coupling profiles. By swapping the extracellular domains of the most distantly related mGlu receptors (the rat group I mGlu1a and the Drosophila melanogaster group II DmGluA receptors), we show that the extracellular domain determines the agonist pharmacological profile and that this domain does not modify the G protein-coupling profile determined by the seven-transmembrane-domain region of mGlu receptors.
Structure and Function of G Protein-Coupled Receptors
Annual Review of Biochemistry, 1994
Al~tract--Application of a molecular genetic techniques has allowed the isolation and identification of more than 50 members of the G protein-coupled receptor family. Their specificities range from sensory receptors such as the opsins and odorant receptors through those for the amines, peptides and other small molecules to those for glycoprotein hormones. These studies make it clear that traditional pharmacological methods, often underestimate receptor diversity.
Journal of Biological Chemistry, 2003
Heptahelical receptor coupling selectivity to G-proteins is controlled by a large contact area that involves several portions of the receptor and each subunit of the Gprotein. In the G-protein ␣ subunit, the C-terminal 5 residues, the N terminus, and the ␣N-1 and ␣4-␣5 loops play important roles. On the receptor side, both the second and third (i2 and i3) intracellular loops as well as the Cterminal tail probably contact these different regions of the G-protein. It is now accepted that the C terminus of the ␣ subunit binds in a cavity formed by the i2 and i3 loops. Among the various G-protein-coupled receptors (GPCRs), class III receptors that include metabotropic glutamate (mGlu) receptors greatly differ from the rhodopsin-like GPCRs, but the contact zone between these receptors and the G-protein is less understood. The C terminus of the ␣ subunit has been shown to play a pivotal role in the selective recognition of class III GPCRs. Indeed, the mGlu2 and mGlu4 and -8 receptors can discriminate between ␣ subunits that differ at the level of their C-terminal end only (such as G qo and G qz ). Here, we examine the role of the i2 loop of mGluRs in the selective recognition of this region of the ␣ subunit. To that aim, we analyzed the coupling properties of mGlu2 and mGlu4 or -8 receptors and chimeras containing the i2 loop of the converse receptor to G-protein ␣ subunits that only differ by their C termini (G qo , G qz , and their point mutants). Our data demonstrate that the central portion of the i2 loop is responsible for the selective recognition of the C-terminal end of the ␣ subunit, especially the residue on position ؊4.
Evolution, structure, and activation mechanism of family 3/C G-protein-coupled receptors
Pharmacology & Therapeutics, 2003
G-protein-coupled receptors (GPCRs) represent one of the largest gene families in the animal genome. These receptors can be classified into several groups based on the sequence similarity of their common heptahelical domain. The family 3 (or C) GPCRs are receptors for the main neurotransmitters glutamate and g-aminobutyric acid, for Ca 2 + , for sweet and amino acid taste compounds, and for some pheromone molecules, as well as for odorants in fish. Although none of these family 3 receptors have been found in plants, members have been identified in ancient organisms, such as slime molds (Dictyostelium) and sponges. Like any other GPCRs, family 3 receptors possess a transmembrane heptahelical domain responsible for G-protein activation. However, most of these identified receptors also possess a large extracellular domain that is responsible for ligand recognition, is structurally similar to bacterial periplasmic proteins involved in the transport of small molecules, and is called a Venus Flytrap module. The recent resolution of the structure of this binding domain in one of these receptors, the metabotropic glutamate 1 receptor, together with the recent demonstration that these receptors are dimers, revealed a unique mechanism of activation for these GPCRs. Such data open new possibilities in the development of drugs aimed at modulating these receptors, and raise a number of interesting questions on the activation mechanism of the other GPCRs.
Journal of Biological Chemistry, 2003
Heptahelical receptor coupling selectivity to G-proteins is controlled by a large contact area that involves several portions of the receptor and each subunit of the Gprotein. In the G-protein ␣ subunit, the C-terminal 5 residues, the N terminus, and the ␣N-1 and ␣4-␣5 loops play important roles. On the receptor side, both the second and third (i2 and i3) intracellular loops as well as the Cterminal tail probably contact these different regions of the G-protein. It is now accepted that the C terminus of the ␣ subunit binds in a cavity formed by the i2 and i3 loops. Among the various G-protein-coupled receptors (GPCRs), class III receptors that include metabotropic glutamate (mGlu) receptors greatly differ from the rhodopsin-like GPCRs, but the contact zone between these receptors and the G-protein is less understood. The C terminus of the ␣ subunit has been shown to play a pivotal role in the selective recognition of class III GPCRs. Indeed, the mGlu2 and mGlu4 and-8 receptors can discriminate between ␣ subunits that differ at the level of their C-terminal end only (such as G qo and G qz). Here, we examine the role of the i2 loop of mGluRs in the selective recognition of this region of the ␣ subunit. To that aim, we analyzed the coupling properties of mGlu2 and mGlu4 or-8 receptors and chimeras containing the i2 loop of the converse receptor to G-protein ␣ subunits that only differ by their C termini (G qo , G qz , and their point mutants). Our data demonstrate that the central portion of the i2 loop is responsible for the selective recognition of the C-terminal end of the ␣ subunit, especially the residue on position ؊4. These data are consistent with the proposal that the Cterminal end of the G-protein ␣ subunit interacts with residues in a cavity formed by the i2 and i3 loops in class III GPCRs, as reported for class I GPCRs. G-protein-coupled-receptors (GPCRs) 1 modulate specific signaling pathways depending on the subset of G-proteins acti