Abstract

GABA_A receptor-associated protein (GABARAP) was isolated previously in a yeast two-hybrid screen using the intracellular loop of the γ2 subunit of the GABA_A receptor as bait. GABARAP has been shown to participate in the membrane-clustering and intracellular-trafficking of GABA_A receptors, including a stimulation of the surface expression of GABA_A receptors. To assess this quantitatively, we used Xenopus laevis oocytes expressing α1β2γ2S-containing GABA_A receptors to demonstrate that coexpression of GABARAP increased net surface levels of GABA_A receptors as shown by both increased GABA currents and surface-expressed protein. This GABARAP stimulation of GABA currents required the receptor γ2 subunit and full-length GABARAP: deletion of the microtubule-binding domain (amino acids 1–22) or disrupting the polymerization of microtubules abolished the enhancement, indicating that the effect of GABARAP was derived from the interaction with microtubules. GABARAP coexpression did not alter the general properties of GABA_A receptors such as sensitivity to GABA or benzodiazepines, but it increased surface levels of receptor protein in oocytes. Rather, it seems to supplement inadequate amounts of endogenous GABARAP to support optimum trafficking and/or stabilization of surface GABA_A receptors.