IDENTIFICATION OF A GEPHYRIN BINDING MOTIF ON THE GLYCINE RECEPTOR-BETA SUBUNIT

The tubulin-binding protein gephyrin copurifies with the inhibitory gl ycine receptor (GlyR) and is essential for its postsynaptic localizati on. Here we have analyzed the interaction between the GlyR and recombi nant gephyrin and identified a gephyrin binding site in the cytoplasmi c loop between the third and fourth transmembrane segments of the beta subunit. GlyR alpha subunits and GABA(A) receptor proteins failed to bind recombinant gephyrin. However, insertion of an 18 residue segment of the GlyR beta subunit into the GABA(A) receptor beta 1 subunit con ferred gephyrin binding both in an overlay assay and in transfected ma mmalian cells. These results indicate that beta subunit expression is essential for the formation of a postsynaptic GlyR matrix.