GABAB receptor subunit 1 binds to proteins affected in 22q11 deletion syndrome

GABAB receptors mediate slow inhibitory effects of the neurotransmitter γ-aminobutyric acid (GABA) on synaptic transmission in the central nervous system. They function as heterodimeric G-protein-coupled receptors composed of the seven-transmembrane domain proteins GABAB1 and GABAB2, which are linked through a coiled-coil interaction. The ligand-binding subunit GABAB1 is at first retained in the endoplasmic reticulum and is transported to the cell surface only upon assembly with GABAB2. Here, we report that GABAB1, via the coiled-coil domain, can also bind to soluble proteins of unknown function, that are affected in 22q11 deletion/DiGeorge syndrome and are therefore referred to as DiGeorge critical region 6 (DGCR6). In transfected neurons the GABAB1–DGCR6 association resulted in a redistribution of both proteins into intracellular clusters. Furthermore, the C-terminus of GABAB2 interfered with the novel interaction, consistent with heterodimer formation overriding transient DGCR6-binding to GABAB1. Thus, sequential coiled-coil interactions may direct GABAB1 into functional receptors.