The γ-aminobutyric acid type A receptor (GABA(A)R)-associated protein GABARAP interacts with gephyrin but is not involved in receptor anchoring at the synapse

γ-Aminobutyric acid type A receptors (GABA(A)Rs) are ligand-gated chloride channels that exist in numerous distinct subunit combinations. At postsynaptic membrane specializations, different GABA(A)R isoforms colocalize with the tubulin-binding protein gephyrin. However, direct interactions of GABA(A)R subunits with gephyrin have not been reported. Recently, the GABA(A)R-associated protein GABARAP was found to bind to the γ2 subunit of GABA(A)Rs. Here we show that GABARAP interacts with gephyrin in both biochemical assays and transfected cells. Confocal analysis of neurons derived from wild-type and gephyrin-knockout mice revealed that GABARAP is highly enriched in intracellular compartments, but not at gephyrin-positive postsynaptic membrane specializations. Our data indicate that GABARAP–gephyrin interactions are not important for postsynaptic GABA(A)R anchoring but may be implicated in receptor sorting and/or targeting mechanisms. Consistent with this idea, a close homolog of GABARAP, p16, has been found to function as a late-acting intra-Golgi transport factor.