Neuroligin

neuroligin 1
Identifiers
Symbol	NLGN1
Entrez	22871
HUGO	14291
OMIM	600568
RefSeq	NP_055747
UniProt	Q8N2Q7
Other data
Locus	Chr. 3 q26.31

neuroligin 2
Identifiers
Symbol	NLGN2
Entrez	57555
HUGO	14290
OMIM	606479
RefSeq	NP_065846
UniProt	Q8NFZ4
Other data
Locus	Chr. 17 p13.1

neuroligin 3
Identifiers
Symbol	NLGN3
Entrez	54413
HUGO	14289
OMIM	300336
RefSeq	NP_001160132
UniProt	Q9NZ94
Other data
Locus	Chr. X q13.1

neuroligin 4X
Identifiers
Symbol	NLGN4X
Entrez	57502
HUGO	14287
OMIM	300427
RefSeq	NP_065793
UniProt	Q8N0W4
Other data
Locus	Chr. X p22.32-22.31

Neuroligin (NLGN), a type I membrane protein, is a cell adhesion protein on the postsynaptic membrane that mediates the formation and maintenance of synapses between neurons. Neuroligins act as ligands for β-Neurexins, which are cell adhesion proteins located presynaptically. Neuroligin and β-neurexin "shake hands," resulting in the connection between two neurons and the production of a synapse. Neuroligins also affect the properties of neural networks by specifying synaptic functions, and they mediate signalling by recruiting and stabilizing key synaptic components. Neuroligins interact with other postsynaptic proteins to localize neurotransmitter receptors and channels in the postsynaptic density as the cell matures. Additionally, neuroligins are expressed in human peripheral tissues and have been found to play a role in angiogenesis. In humans, alterations in genes encoding neuroligins are implicated in autism and other cognitive disorders.

Neuroligins bind with the aid of Ca²⁺ to the α-neurexin LNS (laminin, neurexin and sex hormone-binding globulin-like folding units) domains and to the β-neurexin LNS domain which then establishes a heterophilic trans-synaptic recognition code. Through the observation of the crystal structure of neuroligin-1, it was determined that neuroligin-1 forms a protein dimer when two neurexin-1 beta monomers bind to the neuroligin-1’s two opposite surfaces. This forms a heterotetramer, which contains an interface for binding Ca²⁺. The interaction of neuroligin and neurexin to form a heterotetramer is monitored by alternatively spliced sites located near the binding interface for Ca²⁺ in both the neuroligin-1 and the neurexin-1 beta. Subsequently, the presence of native neuroligin dimers was confirmed in neurons through biochemical detection, which included heterodimers composed of different neuroligin species, increasing the potential heterogeneity of endogenous neuroligin core dimer complexes.

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.

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