Collybistin is a brain specific[1] protein identified as a regulator of the localization of gephyrin, inducing the formation of submembrane gephyrin aggregates that accumulate glycine and GABA receptors.
In 2000 it was identified as a gephyrin binding partner, and an important determinant of inhibitory postsynaptic membrane formation and plasticity.
[1] Gephyrin and collybistin are recruited to developing postsynaptic membranes of inhibitory synapses by the trans-synaptic adhesion molecule neuroligin-2,[2] where they provide the scaffold for the clustering of inhibitory postsynaptic receptors to form a functioning inhibitory synapse.
The gene ARHGEF9 (aka ARHDH) codes for Collybistin.
[3] Where they differ is at the N-terminus in both sequence and whether or not a Src-homology (SH3) domain will be present.