title: Sequences in the amino termini of GABA rho and GABA(A) subunits specify their selective interaction in vitro.
abstract: Molecular cloning has revealed that there are six classes of subunits capable of forming GABA-gated chloride channel receptors. GABA(A) receptors are composed of alpha, beta, gamma, delta, and epsilon/chi subunits, whereas GABA(C) receptors appear to contain rho subunits. However, retinal cells exhibiting GABA(C) responses express alpha, beta, and rho subunits, raising the possibility that GABA(C) receptors may be a mixture of subunit classes. Using in vitro translated protein, we determined that human GABA(A) receptor subunits alpha1, alpha5, and beta1 did not coimmunoprecipitate with full-length rho1, rho2, or the N-terminal domain of rho1 that contains signals for rho-subunit interaction. To explore the molecular mechanism underlying these apparently exclusive combinations, chimeric subunits were created and tested for interaction with the wild-type subunits. Transfer of the N terminus of beta1 to rho1 created a beta1rho1 chimera that coimmunoprecipitated with the alpha1 subunit but not with the rho2 subunit. Furthermore, exchanging the N terminus of the rho1 subunit with the corresponding region of beta1 produced a rho1beta1 chimera that interfered with rho1 receptor expression in Xenopus oocytes, whereas the full-length beta1 subunit had no effect. Together, these results indicate that sequences in the N termini direct assembly of rho subunits and GABA(A) subunits into GABA(C) and GABA(A) receptors, respectively.
authors.affiliation: Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA.
authors.forename: A S
authors.initials: AS
authors.lastname: Hackam
authors.forename: T L
authors.initials: TL
authors.lastname: Wang
authors.forename: W B
authors.initials: WB
authors.lastname: Guggino
authors.forename: G R
authors.initials: GR
authors.lastname: Cutting
mesh_terms: D000818:Animals; D002678:Chimera; D004285:Dogs; D004347:Drug Interactions; D006801:Humans; D009865:Oocytes / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011233:Precipitin Tests; D011817:Rabbits; D018079:Receptors, GABA / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D011963:Receptors, GABA-A / Q000502:physiology; D014981:Xenopus
chemical_list: D010446:Peptide Fragments; D018079:Receptors, GABA; D011963:Receptors, GABA-A