The epilepsy mutation, gamma2(R43Q) disrupts a highly conserved inter-subunit contact site, perturbing the biogenesis of GABAA receptors.
Given the association of a gamma2 mutation (R43Q) with epilepsy and the reduced cell surface expression of mutant receptors, we investigated a role for this residue in alpha1beta2gamma2 receptor assembly when present in each subunit. Regardless of which subunit contained the mutation, mutant GABA(A) receptors assembled poorly into functional cell surface receptors. The low level of functional expression gives rise to reduced GABA EC50s (alpha1(R43Q)beta2gamma2 and alpha1beta2(R43Q)gamma2) or reduced benzodiazepine potentiation of GABA-evoked currents (alpha1beta2gamma2(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, gamma2(R43Q) may form non-productive subunit interactions leading to a dominant negative effect on other receptor subtypes.
Hales
Tim G
TG
Department of Pharmacology and Physiology, The George Washington University, 2300 Eye Street NW, Washington, DC 20037, USA.
Tang
Haiyan
H
Bollan
Karen A
KA
Johnson
Sara J
SJ
King
Dale P
DP
McDonald
Neil A
NA
Cheng
Aixin
A
Connolly
Christopher N
CN
D000595:Amino Acid Sequence; D000818:Animals; D001120:Arginine / Q000235:genetics; D019556:COS Cells; D002522:Chlorocebus aethiops; D004827:Epilepsy / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D017354:Point Mutation; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011963:Receptors, GABA-A / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship; D014162:Transfection
C546280:Gabrg2 protein, mouse; D021122:Protein Subunits; D011963:Receptors, GABA-A; D011993:Recombinant Fusion Proteins; D001120:Arginine