Regulation of synaptic inhibition by phosphodependent binding of the AP2 complex to a YECL motif in the GABA_A receptor γ2 subunit

The regulation of the number of γ2-subunit-containing GABA _A receptors (GABA_ARs) present at synapses is critical for correct synaptic inhibition and animal behavior. This regulation occurs, in part, by the controlled removal of receptors from the membrane in clathrin-coated vesicles, but it remains unclear how clathrin recruitment to surface γ2-subunit-containing GABA_ARs is regulated. Here, we identify a γ2-subunit-specific Yxxφ-type-binding motif for the clathrin adaptor protein, AP2, which is located within a site for γ2-subunit tyrosine phosphorylation. Blocking GABA_AR-AP2 interactions via this motif increases synaptic responses within minutes. Crystallographic and biochemical studies reveal that phosphorylation of the Yxxφ motif inhibits AP2 binding, leading to increased surface receptor number. In addition, the crystal structure provides an explanation for the high affinity of this motif for AP2 and suggests that γ2-subunit-containing heteromeric GABA_ARs may be internalized as dimers or multimers. These data define a mechanism for tyrosine kinase regulation of GABA_AR surface levels and synaptic inhibition.