Cloning and Characterization of a GABAA Receptor γ 2 Subunit Variant

Abstract

We have cloned a novel γ-aminobutyric acid type A (GABAA) receptor γ2 subunit variant named γ2XL. γ2XL contains an alternatively spliced exon, resulting in the addition of 40 amino acids to the N-terminal extracellular domain between Ser171 and Tyr172. We show that γ2XL failed to localize to the cell surface when it was coexpressed with the α2 and β3 subunits in human embryonic kidney 293 cells. Expression of γ2XL in 293 cells suppressed GABA A receptor binding in a dose-dependent manner by preventing GABA A receptor cell-surface localization. We also generated a γ2 mutant with Ser171 and Tyr172 converted to glycine and threonine, respectively. We demonstrate that this mutant has a significantly lower affinity for the γ2 and β1 subunits and failed to reach the cell surface when coexpressed with these subunits. Together, our results indicate that Ser 171 and Tyr172 in the γ2 subunit constitute a critical motif. When this motif is disrupted by insertion of the alternative exon, access of the γ2 subunit to the cell surface is prevented.