Heterodimerization of a functional GABA(B) receptor is mediated by parallel coiled-coil alpha-helices

A detailed understanding of GABA(B) receptor assembly is an important issue in view of its role as attractive target for treatment of epilepsy, anxiet y, depression, cognitive defects, and nociceptive disorders. Heteromerizati on of GABA(B)-R1 and GABA(B)-R2 sulbunits is a prerequisite for the formati on of a functional GABA(B) receptor. Each individual subunit contains one s tretch of similar to 30 amino acid residues within its intracellular C-term inal domain that mediates heteromer formation. To investigate the mechanism of the GABA(B)-R1/GABA(B)-R2 interaction and to assess the subunit stoichi ometry of the complex, recombinant polypeptide chain fragments containing t he heteromerization site were produced by heterologous gene expression in E scherichia coli. When mixed in equimolar amounts, these peptides preferenti ally formed parallel coiled-coil heterodimers under physiological buffer co nditions. This demonstrates that the short C-terminal regions are sufficien t to determine the specificity of interaction between GABA(B) receptor subu nits. In contrast, isolated GABA(B) -R1 peptides folded into relatively uns table homodimers, whereas GABA(B)-R2 peptides were largely unstructured. To gether with the data reported in the literature, the results presented here indicate that the functional GABA(B) receptor is a heterodimer assembled b y parallel coiled-coil alpha-helices.