the transmembrane helices TM3 and TM4 of alpha and beta subunits of the GABAA receptor. Gephyrin displaces GABA receptors from the GABARAP/P130 complex, then brings the receptors to the synapse. Once at the synapse, the protein binds to collybistin and neuroligin 2. In cells, gephyrin appears to form oligomers of at least three subunits. Several splice variants have been described that prevent this oligomerization without influencing the affinity for receptors. They nevertheless affect the composition of inhibitory synapses and can even play a role in diseases like epilepsy. The gephyrin protein is also required for insertion of molybdenum into molybdopterin. As aforementioned, gephyrin also catalyzes terminal two steps of Moco biosynthesis. In the penultimate step, N-terminal G domain adenylate the apo form of the molybdopterin to form the intermediate adenylated molybdopterin. In the terminal step, the C-terminal E domain catalyzes the deadenylation and also the metal insertion mechanism. Clinical significance Humans with temporal lobe epilepsy have been found to have abnormally low levels of gephyrin in their temporal lobes. In animal models, a total lack of gephyrin results in stiff muscles and death immediately after birth. Stiff muscles are also a symptom of startle disease, that can be caused by a mutation in the gephyrin gene. And if a person produces auto-antibodies against gephyrin, this can even result in stiff person syndrome. Yin-yang sequences At some point in human history, there was a DNA sequence encompassing gephyrin that split and followed two divergent evolutionary paths. These types of splits can occur when two populations become isolated from each other or when a chromosomal region does not experience recombination events. The two sequences that split from the ancestral sequence each acquired more than a hundred mutations that subsequently became common. This happened in a relatively short time on an evolutionary scale, as hundreds of mutations were fixed in distinct ‘yin’ and ‘yang’ sequences prior to human migration to Asia. It has been reported that currently Asians carry nearly equal numbers of yin and yang sequences and global populations representing every major human ancestry possess both yin and yang sequences. The existence of this massive yin-yang pattern suggests that two completely divergent evolutionary paths rapidly progressed during human history, presumably achieving the common goal of enhancing regulation of gephyrin. Interactions GPHN has been shown to interact with Mammalian target of rapamycin and ARHGEF9. References Further reading External links