The heteromeric GABA-B receptor recognizes G-protein alpha subunit C-termini

Neuropharmacology. 1999 Nov;38(11):1657-66. doi: 10.1016/s0028-3908(99)00135-5.


The recently cloned GABA-B receptors are related to the metabotropic glutamate receptors (mGlu receptors), the Ca2+-sensing receptor and one group of vomeronasal receptors. The GABA-B receptors likely function in a heterodimeric form, constituted of GABA-BR1 and GABA-BR2. This novel feature in the G-protein coupled receptors (GPCRs) structure raises questions as to the mechanism of recognition of G-proteins by such receptors. In the present study we show that the GABA-BR1 and BR2 subunits form a functional receptor that recognizes the extreme C-termini of the G alpha i and G alpha o proteins when expressed in HEK293 cells. Indeed, heteromeric GABA-BR1/BR2 receptors do not activate PLC when co-expressed with G alpha q, but do so when co-expressed with the chimeric G alpha qi5 or G alpha qo5 subunits, the G alpha q subunit in which the 5 C-terminal residues are those of G alpha i or G alpha o, respectively. Interestingly, the heteromeric GABA-B receptor did not activate the chimeric G alpha qz5 subunit that contains the 5 C-terminal residues of G alpha z. Among the three residues that are distinct between G alpha qo5 and G alpha qz5 (at position -5, -4 and -1), the amino acid residue at position -4 of G alpha o proteins is critical for specifying the coupling selectivity with the receptor and residue -5 influences the coupling efficacy. Interestingly, these findings correspond to data obtained with the mGluR2 receptor, a distant relative of GABA-B proteins. This shows that the same molecular determinants of the G-protein alpha-subunits are involved in the specific recognition of both the heteromeric GABA-B receptors and the other GPCRs.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cell Line
  • Cells, Cultured
  • GABA Agonists / metabolism
  • GABA Agonists / pharmacology
  • GTP-Binding Protein alpha Subunits, Gi-Go / chemistry*
  • GTP-Binding Protein alpha Subunits, Gi-Go / metabolism
  • Guanosine 5'-O-(3-Thiotriphosphate) / metabolism
  • Humans
  • Inositol Phosphates / metabolism*
  • Kidney / cytology
  • Kidney / embryology
  • Rats
  • Receptors, GABA-B / chemistry*
  • Receptors, GABA-B / genetics
  • Receptors, GABA-B / metabolism
  • gamma-Aminobutyric Acid / metabolism
  • gamma-Aminobutyric Acid / pharmacology


  • GABA Agonists
  • Inositol Phosphates
  • Receptors, GABA-B
  • Guanosine 5'-O-(3-Thiotriphosphate)
  • gamma-Aminobutyric Acid
  • GTP-Binding Protein alpha Subunits, Gi-Go