Assembly rules for GABA(A) receptor complexes in the brain

GABA(A) receptor (GABA(A)R) pentamers are assembled from a pool of 19 subunits, and variety in subunit combinations diversifies GABA(A)R functions to tune brain activity. Pentamers with distinct subunit compositions localize differentially at synaptic and non-synaptic sites to mediate phasic and tonic inhibition, respectively. Despite multitudes of theoretical permutations, limited subunit combinations have been identified in the brain. Currently, no molecular model exists for combinatorial GABA(A)R assembly in vivo. Here, we reveal assembly rules of native GABA(A)R complexes that explain GABA(A)R subunit subcellular distributions using mice and Xenopus laevis oocytes. First, α subunits possess intrinsic signals to segregate into distinct pentamers. Second, γ2 is essential for GABA(A)R assembly with Neuroligin-2 (NL2) and GARLHs, which localize GABA(A)Rs at synapses. Third, δ suppresses α6 synaptic localization by preventing assembly with GARLHs/NL2. These findings establish the first molecular model for combinatorial GABA(A)R assembly in vivo and reveal an assembly pathway regulating GABA(A)R synaptic localization.