Neuroligin

Neuroligin (NLGN), a type I membrane protein, is a protein on the postsynaptic membrane that mediates synapse formation between neurons. Neuroligins mediate signaling across the synapse and affect the properties of neural networks by specifying synaptic functions. In humans, alterations in genes encoding neuroligins are implicated in autism and other cognitive diseases. It has been shown that neuroligin expression induces contact-mediated presynaptic differentiation in contacting axons.

The extracellular domain of NLGN consists mostly of a region that is homologous to acetylcholinesterases, but the amino acids important for catalysis in AChE are not conserved in NLGN, which lack esterase activity. Furthermore, this AChE homologous region is crucial for the proper function of NLGN.

Neuroligins act as ligands for β-Neurexins, which are located presynaptically. Neuroligin and β-neurexin "shake hands," resulting in the connection between the two neurons and the production of a synapse. Additionally, neuroligin has also been found to play a role in angiogenesis.

Neuroligins also operate in honeybees and their functional roles in insects are likely similar to those in vertebrates.

Known neuroligin genes include NLGN1, NLGN2, NLGN3, NLGN4X, and NLGN5.