Functional heterogeneity of gephyrins

Postsynaptic clustering of the glycine receptor requires the cytoplasmic pr otein gephyrin, which interacts with the receptor beta subunit. Several var iants of gephyrin are generated by alternative splicing and differ by the p resence of short amino acid sequences (cassettes) in the N-terminal half of the molecule. In this work, seven isoforms of gephyrin were cloned from ad ult rat spinal cord, some of then containing new cassettes. The relationshi ps between gephyrin structure and recognition of glycine receptor beta subu nit were analyzed. This was carried out by GST-pull-down assays using the b eta subunit cytoplasmic loop and cotransfection experiments of GFP-tagged g ephyrins with an alpha1 subunit bearing the gephyrin-binding site of the be ta subunit. Data demonstrated that not all gephyrin molecules can bind to t he beta subunit. Identified cassettes modulate this interaction. It is thus concluded that the function of gephyrin in synapse formation can rely on a structure acquired through cassette combinations.