The epilepsy mutation, γ2(R43Q) disrupts a highly conserved inter-subunit contact site, perturbing the biogenesis of GABA_Areceptors

Given the association of a ?2 mutation (R43Q) with epilepsy and the reduced cell surface expression of mutant receptors, we investigated a role for this residue in a1ß2?2 receptor assembly when present in each subunit. Regardless of which subunit contained the mutation, mutant GABAA receptors assembled poorly into functional cell surface receptors. The low level of functional expression gives rise to reduced GABA EC50s (a1(R43Q)ß2?2 and a1ß2(R43Q)?2) or reduced benzodiazepine potentiation of GABA-evoked currents (a1ß2?2(R43Q)). We determined that a 15-residue peptide surrounding R43 is capable of subunit binding, with a profile that reflected the orientation of subunits in the pentameric receptor. Subunit binding is perturbed when the R43Q mutation is present suggesting that this residue is critical for the formation of inter-subunit contacts at (+) interfaces of GABAA subunits. Rather than being excluded from receptors, ?2(R43Q) may form non-productive subunit interactions leading to a dominant negative effect on other receptor subtypes.