Gephyrin (GPHN, from molybdopterin adenyltransferase) is a 90­94kD member of both the MoaB and MoeA families of proteins. It has limited expression, being found in hepatocytes and neurons. In neurons, gephyrin is a postsynaptic density cytoplasmic protein that interacts with the subunits of glycine and GABA­A receptors. This interaction is mediated by the ability of gephyrin to form hexameric lattices that act as scaffolds that link the subunits of the two inhibitory receptors to the cell's underlying tubulin network. In addition, the gephyrin lattice may also interact with NLG­1 and ­2, suggesting a role for gephyrin in the regulation of glutamatergic synapses. Gephyrin is also known to participate in the synthesis of molybdenum cofactor. This cofactor binds molybdenum, making it available to sulfite and aldehyde reductase. Human gephyrin is 736 amino acids (aa) in length. It contains a 181aa N­terminal G­domain that possesses MPT Mo­transferase activity (aa14­166) and a homotrimer interface motif, followed by a 420aa C­terminal region (aa319­738) that contains an MPT adenyltransferase domain (aa326­736) with an embedded homodimerization motif. There are at least five utilized Ser/Thr phosphorylation sites. Multiple splice variants exist, and represent peptide insertions at multiple sites. There is a 13aa insertion after Glu98, a 33aa insertion after Ser243, and 15, 19, 21 and 24aa insertions after Lys288. Over aa2­188, human and mouse Gephyrin are identical in amino acid sequence.