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

Abstract

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.