Heterodimerization is required for the formation of a functional GABAB receptor

Abstract

GABA (gamma-aminobutyric acid) is the main inhibitory neurotransmitter in the mammalian central nervous system, where it exerts its effects through ionotropic (GABA(A/C)) receptors to produce fast synaptic inhibition and metabotropic (GABA(B)) receptors to produce slow, prolonged inhibitory signals. The gene encoding a GABA(B) receptor (GABA(B)R1) has been cloned; however, when expressed in mammalian cells this receptor is retained as an immature glycoprotein on intracellular membranes and exhibits low affinity for agonists compared with the endogenous receptor on brain membranes. Here we report the cloning of a complementary DNA encoding a new subtype of the GABAB receptor (GABA(B)R2), which we identified by mining expressed-sequence-tag databases. Yeast two-hybrid screening showed that this new GABA(B)R2-receptor subtype forms heterodimers with GABA(B)R1 through an interaction at their intracellular carboxy-terminal tails. Upon expression with GABA(B)R2 in HEK293T cells, GABA(B)R1 is terminally glycosylated and expressed at the cell surface. Co-expression of the two receptors produces a fully functional GABA(B) receptor at the cell surface; this receptor binds GABA with a high affinity equivalent to that of the endogenous brain receptor. These results indicate that, in vivo, functional brain GABA(B) receptors may be heterodimers composed of GABA(B)R1 and GABA(B)R2.

Surface expression of metabotropic glutamate receptor variants mGluR1a and mGluR1b in transfected HEK293 cells

“…In this receptor, extracellular domains and heptahelical domains of two subunits GB1 and GB2 have to assemble to form a functional receptor complex (Jones et al, 1998;Kaupmann et al, 1998;White et al, 1998). The C-termini are not crucial for G-protein activation by GABAb receptor as truncation of these does not prevent coupling to Gi/o pathway (Pagano et al, 2001).…”

“…The GABAb receptor is formed by subunits GB1 and GB2 that have to assemble in functional complexes (Jones et al, 1998;Kaupmann et al, 1998;White et al, 1998). The carboxyl-termini of the GABAb receptor are involved in quality-control of proper heterodimerization but are not mandatory for G-protein coupling (Pagano et al, 2001).…”

Constitutive, agonist-accelerated, recycling and lysosomal degradation of GABAB receptors in cortical neurons

“…GABA B receptors are heterodimeric G protein-coupled receptors constituted of two different seven-transmembrane proteins termed GABA B1 and GABA B2 (Jones et al, 1998;Kaupmann et al, 1998;Kuner et al, 1999;Martin et al, 1999;Ng et al, 1999;White et al, 1998). Two main variants of GABA B1 that differ in their N-terminal domain are generated by alternative promoter usage (Steiger et al, 2004) and give rise to two GABA B receptor subtypes, GABA B1a /GABA B2 and GABA B1b /GABA B2 .…”

Optogenetic analysis of GABABreceptor signaling inCaenorhabditis elegansmotor neurons

“…locomotion; metabotropic GABA receptor; plasticity; channelrhodopsin-2; excitatory-inhibitory balance IN MAMMALS, GABA B receptors are extrasynaptic, high-affinity G protein-coupled receptors (GPCRs) that either act as presynaptic autoreceptors on GABAergic neurons or detect spillover GABA, released at nearby synapses (Bettler et al 2004). GABA B receptors are obligate heterodimers of B1 and B2 subunits (Jones et al 1998;White et al 1998) that together with auxiliary subunits (KCTD proteins) appear to form tetramers or even higher order oligomers (Schwenk et al 2010). GABA B receptors can modulate the function of excitatory neurons by heterosynaptic inhibition, via signaling through heterotrimeric G proteins (through "released" G␤␥ subunits), to inhibit presynaptic voltage-gated Ca 2ϩ -channels (Herlitze et al 1996;Ikeda 1996).…”