Abstract
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) channels1. Molecular cloning revealed that functional GABAB receptors are formed by the heteromeric assembly of GABAB1 with GABAB2 subunits2,3,4,5. However, cloned GABAB(1,2) receptors failed to reproduce the functional diversity observed with native GABAB receptors6,7,8. 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.
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Acknowledgements
Author Contributions
We thank J. P. Adelman and H. R. Brenner for discussions and critical reading of the manuscript, and A. Haupt and K. Kaupmann for help with bioinformatics and shRNA experiments, respectively. This work was supported by grants from the Deutsche Forschungsgemeinschaft to B.F. (SFB 746/TP16; SFB 780/A3; EXC294) and to A.K. (SFB 780/A2), by grants from the Wellcome Trust (ISRF), the EU Synapse and the GACR (309/06/1304) to R.T., and by grants from the Swiss Science Foundation (3100A0-117816), the Fridericus Stiftung and the European Community’s 7th Framework Programme (FP7/2007-2013) under Grant Agreement 201714 to B.B.
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J.S., M.M., G.Z. and R.T. are equally contributing first authors. J.S., W.B., V.R., U.S. and B.F. performed proteomic analysis, biochemistry and evaluation of mass spectrometry. M.M., J.Y.T., M.G., J.T., T.F., M.R. and K.I. performed in situ hybridization, cellular biology, mouse work and KCTD antibody generation. G.Z., R.T., R.S. and M.R. conducted the electrophysiological recordings on oocytes, cultured cells and neurons. A.U., E.T. and A.K. performed electron microscopy. B.F., B.B. and U.S. initiated, designed and supervised the study. B.F. and B.B. wrote the manuscript.
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Schwenk, J., Metz, M., Zolles, G. et al. Native GABAB receptors are heteromultimers with a family of auxiliary subunits. Nature 465, 231–235 (2010). https://doi.org/10.1038/nature08964
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DOI: https://doi.org/10.1038/nature08964
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