User:JoeyD Valle/Neurexin

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Neurexins are neuronal cell-surface proteins with up to thousands of isoforms. These isoforms are generated by alternative splicing of transcripts from six promoters in three genes. The structure of neurexins resembles cell-surface receptors with a modular architecture suggestive of a sequential assembly during evolution. Neurexins probably perform multiple functions in the brain. They participate in intercellular junctions in which β-neurexins tightly bind to a second class of neuronal cell-surface receptors called neuroligins. Intracellularly, the neurexin/neuroligin junction is bound by CASK on the neurexin side and PSD95 on the neuroligin side. CASK and PSD95 are homologous membrane-associated guanylate kinases that bind to the neurexin/neuroligin junction via PDZ domains, creating an asymmetric junction (neurexin/neuroligin) with similar intracellular binding partners. In addition to a function as cell-adhesion molecules, neurexins may also serve as a signalling receptor, because a class of ligands for α-neurexins called neurexophilins is similar to peptide hormones. Finally, at least one neurexin isoform, neurexin Iα, represents a high-affinity receptor for α-latrotoxin, which is a potent excitatory neurotoxin. Thus, neurexins constitute a large family of neuronal receptors that may be involved in multiple interactive functions between neurons.

Neurexins are transmembrane proteins that function primarily at the cell surface of neurons [1-3]. Neurexin variants are essential for Ca2+-dependent transmission at diverse types of excitatory and inhibitory synapses from the central and peripheral nervous system

additional molecules associated with the synaptic cleft have been identified as binding partners, including neurexophilin [17-19], dystroglycan [20], LRRTM proteins [21,22] and cerebellin

There are three neurexin genes in the mammalian genome [2,3,28]. In addition, a member of the Caspr/paranodin/CTNAP family is named ‘neurexin 4’ for historical reasons but in fact contains a domain structure that is only more distantly related