Identification of residues within GABA(A) receptor alpha subunits that mediate specific assembly with receptor beta subunits

GABA(A) receptors can be constructed from a range of differing subunit isof orms: alpha, beta, gamma, delta, and epsilon. Expression studies have revea led that production of GABA-gated channels is achieved after coexpression o f alpha and beta subunits. The expression of a gamma subunit isoform is ess ential to confer benzodiazepine sensitivity on the expressed receptor. Howe ver, how the specificity of subunit interactions is controlled during recep tor assembly remains unknown. Here we demonstrate that residues 58-67 withi n alpha subunit isoforms are important in the assembly of receptors compris ed of alpha beta and alpha beta gamma subunits. Deletion of these residues from the alpha 1 or alpha 6 subunits results in retention of either alpha s ubunit isoform in the endoplasmic reticulum on coexpression with the beta 3 , or beta 3 and gamma 2 subunits. Immunoprecipitation revealed that residue s 58-67 mediated oligomerization of the alpha 1 and alpha 3 subunits, but w ere without affect on the production of alpha/gamma complexes. Within this domain, glutamine 67 was of central importance in mediating the production of functional alpha 1 beta 3 receptors. Mutation of this residue resulted i n a drastic decrease in the cell surface expression of alpha 1 beta 3 recep tors and the resulting expression of beta 3 homomers. Sucrose density gradi ent centrifugation revealed that this residue was important for the product ion of a 9S alpha 1 beta 3 complex representing functional GABA(A) receptor s. Therefore, our studies detail residues that specify GABA(A) receptor alpha beta subunit interactions. This domain, which is conserved in all alpha sub unit isoforms, will therefore play a critical role in the assembly of GABA( A) receptors composed of alpha beta and alpha beta gamma subunits.