The N-terminal domain of gamma-aminobutyric Acid(B) receptors is sufficient to specify agonist and antagonist binding.
The recently identified gamma-aminobutyric acid type B receptors (GABA(B)Rs) share low sequence similarity with the metabotropic glutamate (mGlu) receptors. Like the mGlu receptors, the N-terminal extracellular domain (NTED) of GABA(B)Rs is proposed to be related to bacterial periplasmic binding proteins (PBPs). However, in contrast to the mGlu receptors, the GABA(B)Rs lack a cysteine-rich region that links the PBP-like domain to the first transmembrane domain. This cysteine-rich region is necessary for the PBP-like domain of mGlu receptors to bind glutamate. To delimit the ligand-binding domain of GABA(B)Rs, we constructed a series of chimeric GABA(B)R1/mGluR1 and truncated GABA(B)R1 receptor mutants. We provide evidence that despite the lack of a cysteine-rich region, the NTED of GABA(B)Rs contains all of the structural information that is necessary and sufficient for ligand binding. Moreover, a soluble protein corresponding to the NTED of GABA(B)Rs reproduces the binding pharmacology of wild-type receptors. This demonstrates that the ligand-binding domain of the GABA(B)Rs can correctly fold when dissociated from the transmembrane domains.
Novartis Pharma AG, Nervous System Research, Basel, Switzerland.
B
B
Malitschek
C
C
Schweizer
M
M
Keir
J
J
Heid
W
W
Froestl
J
J
Mosbacher
R
R
Kuhn
J
J
Henley
C
C
Joly
J P
JP
Pin
K
K
Kaupmann
B
B
Bettler
D000818:Animals; D000906:Antibodies / Q000276:immunology; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D000939:Epitopes / Q000276:immunology; D058786:GABA-B Receptor Agonists; D058788:GABA-B Receptor Antagonists; D008024:Ligands; D008322:Mammals; D011487:Protein Conformation; D018080:Receptors, GABA-B / Q000378:metabolism*; D017470:Receptors, Glutamate / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D018411:Spodoptera; D014162:Transfection
D000906:Antibodies; D000939:Epitopes; D058786:GABA-B Receptor Agonists; D058788:GABA-B Receptor Antagonists; D008024:Ligands; D018080:Receptors, GABA-B; D017470:Receptors, Glutamate; D011993:Recombinant Fusion Proteins