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To test the hypothesis that functional diversity of native [GABA.sub.B] receptors results from additional as yet unknown subunits, a proteomic analysis was performed with a recently developed approach combining affinity [...], [GABA.sub.B] receptors are the G-protein-coupled receptors for γ-aminobutyric acid (GABA), the main inhibitory neurotransmitter in the brain. They are expressed in almost all neurons of the brain, where they regulate synaptic transmission and signal propagation by controlling the activity of voltage-gated calcium ([Ca.sub.v]) and inward-rectifier potassium ([K.sub.ir]) channels (1). Molecular cloning revealed that functional [GABA.sub.B] receptors are formed by the heteromeric assembly of [GABA.sub.B1] with [GABA.sub.B2] subunits (2-5). However, cloned [GABA.sub.B(12)] receptors failed to reproduce the functional diversity observed with native [GABA.sub.B] receptors (6-8). Here we show by functional proteomics that [GABA.sub.B] receptors in the brain are high-molecular-mass complexes of [GABA.sub.B1], [GABA.sub.B2] and members of a subfamily of the KCTD (potassium channel tetramerization domain-containing) proteins. KCTD proteins 8,12,12b and 16 show distinct expression profiles in the brain and associate tightly with the carboxy terminus of [GABA.sub.B2] as tetramers. This co-assembly changes the properties of the [GABA.sub.B(1,2)] core receptor: the KCTD proteins increase agonist potency and markedly alter the G-protein signalling of the receptors by accelerating onset and promoting desensitization in a KCTD-subtype-specific manner. Taken together, our results establish the KCTD proteins as auxiliary subunits of [GABA.sub.B] receptors that determine the pharmacology and kinetics of the receptor response.

The properties of glycine receptors (GlyRs) depend upon their subunit composition. While the prevalent adult forms of GlyRs are heteromers, previous reports suggested functional a homomeric receptors in mature nervous tissues. Here we show two functionally different GlyRs populations in the rat medial nucleus of trapezoid body (MNTB). Postsynaptic receptors formed a1/β-containing clusters on somatodendritic domains of MNTB principal neurons, colocalizing with glycinergic nerve endings to mediate fast, phasic IPSCs. In contrast, presynaptic receptors on glutamatergic calyx of Held terminals were composed of dispersed, homomeric a1 receptors. Interestingly, the parent cell bodies of the calyces of Held, the globular bushy cells of the cochlear nucleus, expressed somatodendritic receptors (a1/β heteromers) and showed similar clustering and pharmacological profile as GlyRs on MNTB principal cells. These results suggest that specific targeting of GlyR β-subunit produces segregation of GlyR subtypes involved in two different mechanisms of modulation of synaptic strength. [ABSTRACT FROM AUTHOR]

GABAB receptors are the G-protein-coupled receptors for γ-aminobutyric acid (GABA), the main inhibitory neurotransmitter in the brain. They are expressed in almost all neurons of the brain, where they regulate synaptic transmission and signal propagation by controlling the activity of voltage-gated calcium (Cav) and inward-rectifier potassium (Kir) channels. Molecular cloning revealed that functional GABAB receptors are formed by the heteromeric assembly of GABAB1 with GABAB2 subunits. However, cloned GABAB(1,2) receptors failed to reproduce the functional diversity observed with native GABAB receptors. Here we show by functional proteomics that GABAB receptors in the brain are high-molecular-mass complexes of GABAB1, GABAB2 and members of a subfamily of the KCTD (potassium channel tetramerization domain-containing) proteins. KCTD proteins 8, 12, 12b and 16 show distinct expression profiles in the brain and associate tightly with the carboxy terminus of GABAB2 as tetramers. This co-assembly changes the properties of the GABAB(1,2) core receptor: the KCTD proteins increase agonist potency and markedly alter the G-protein signalling of the receptors by accelerating onset and promoting desensitization in a KCTD-subtype-specific manner. Taken together, our results establish the KCTD proteins as auxiliary subunits of GABAB receptors that determine the pharmacology and kinetics of the receptor response. [ABSTRACT FROM AUTHOR]